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To overcome transmission and thermalization losses from single-junction solar cells, the two-terminal tandem cell configuration is one of the most widely followed approaches. Unfortunately, the need to match the current from both cells, in addition to the fabrication of an interlayer with excellent optical and electronic performances, makes such two-terminal configurations a challenging approach. Herein, the fabrication of a four-terminal tandem incorporating a front transparent cell made using a 7¿nm Ag back electrode and a PM6:L8-BO blend which exhibits a bandgap close to the optimal according to the detailed balance theory is reported. For the opaque back cell in such tandem, a PTB7-Th:O6T-4F blend is used. A 16.94% power conversion efficiency is achieved when such two cells are configured in a four-terminal device separated by a WO3/LiF/WO3 multilayer providing an optimal light absorption distribution among the two cells., The authors acknowledge Dr. Mariia Kramarenko for her help with the detailed balance calculations. F.B.T. and J. M. acknowledge the financial support by the European Commission through the LICROX project (grant no. 951843) and the SOREC2 project (101084326). In addition, the work was partially funded by Ministerio de Ciencia e Innovación (grants nos. CEX2019-000910-S and PID2020-112650RB-I00), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya through Centres de Recerca de Catalunya. F.B.T acknowledges financial support from the Agencia Estatal de Investigación (grant no. PRE2018-084881)., Peer Reviewed, Postprint (published version)

Recent developments in Sb2Se3 van der Waals material as an absorber candidate for thin film photovoltaic applications have demonstrated the importance of surface management for improving the conversion efficiency of this technology. Sb2Se3 thin films’ versatility in delivering good efficiencies in both superstrate and substrate configurations, coupled with a compatibility with various low-temperature deposition techniques (below 500 °C and often below 350 °C), makes them highly attractive for advanced photovoltaic applications. This study presents a comparative analysis of the most effective chemical etchings developed for related thin film chalcogenide technologies to identify and understand the most appropriate surface chemical treatments for Sb2Se3 in substrate configuration, synthesized using a sequential process at very low temperatures (320 °C). Eight different chemical etchings were tested and investigated, and the results show that only KCN-based solutions lead to an improvement in the solar cell’s performance, primarily due to an increase in the fill factor. Surface analysis of the samples shows that KCN etching produces very Sb-rich surfaces that do not affect the properties of the bulk. It is proposed that this Sb-rich interface inverts the surface polarity, creating a “buried junction” with CdS, thereby explaining the improvement of the fill factor of the devices, as confirmed by device modeling. The results of this study underscore the importance of surface management in low-temperature synthesized Sb2Se3 absorbers, where Sb-rich interfaces are crucial for achieving high-efficiency devices. This research contributes to ongoing efforts to improve the performance of Sb2Se3 thin film photovoltaic technology and could pave the way for the development of more efficient solar cells with optimized interfaces., Postprint (published version)

This bachelor's thesis focuses on the design of the solar panels to Cube-Cat-8, the upcoming satellite that UPC will send into space to analyse aurora borealis. In the NanoSatLab laboratory, I have carried out numerous designs, seeking to maximise the surface area of solar cells while simultaneously respecting the structural design of the satellite. To choose the best design, I conducted comparative vibration analyses to assess the structural performance of different designs and select the one that yielded the best results. Additionally, I performed two tests on solar cells, involving the verification of their operation and measurement of short-circuit current under AM0 conditions. Finally, in the last phase of the work, I focused on the design of electrical schematics for the realization of PCBs and thus ensure an efficient interconnection of the system to contribute to the success of the mission., Este trabajo de fin de grado se centra en el diseño de los paneles solares destinados al Cube-Cat-8, el próximo satélite que la UPC enviará al espacio con el objetivo de analizar auroras boreales. En el UPC NanoSatLab, he realizado numerosos diseños, buscando maximizar tanto como fuera posible la superficie de las células solares, pero respetando al mismo tiempo el diseño estructural del satélite. Para elegir el mejor, realicé análisis de vibraciones comparativos para evaluar el rendimiento estructural de los diferentes diseños y seleccionar el que ofrecía mejores resultados. Además, llevé a cabo dos pruebas de células solares, consistentes en verificar su funcionamiento y medir la corriente en cortocircuito en condiciones de AM0. Finalmente, en la última fase del trabajo, me centré en el diseño de los esquemáticos eléctricos para la realización de las PCBs y asegurar así una eficiente interconexión del sistema para contribuir al éxito de la misión., Aquest treball de fi de grau es centra en el disseny dels panells solars destinats al Cube-Cat-8, el proper satèl·lit que la UPC enviarà a l'espai amb l'objectiu d'analitzar les aurores boreals. Al UPC NanoSatLab, he realitzat nombrosos dissenys, buscant maximitzar tant com fos possible la superfície de cel·les solars però respectant alhora el disseny estructural del satèl·lit. Per triar el millor, vaig fer anàlisis de vibracions comparatius per tal d'avaluar el rendiment estructural dels diferents dissenys i triar el que millors resultats donava. A més, vaig realitzar dues proves de cel·les solars, consistents en la verificació del seu funcionament i mesura de la corrent en curtcircuit en condicions d'AM0. Finalment, en l'última fase del treball, em vaig centrar en el disseny dels esquemàtics elèctrics per a la realització de les PCBs i assegurar així una eficient interconnexió del sistema per contribuir a l'èxit de la missió.

Organic solar cells are attracting attention due to being light-weight, low-cost and having tunable optical properties, which make them interesting for different applications such as integrated building and agrovoltaics. For such applications, the angle of incidence of light is given by architectural limitations and thus it is important to understand what controls the dependence of solar cell performance on the angle of incidence of light. Here the angular dependence for an organic solar cell is measured to quantify the effects of a reduction in light intensity, of an increased optical path within the active layer and of the angular variation of the reflection losses, Las células solares orgánicas llaman la atención por ser ligeras, de bajo coste y tener propiedades ópticas ajustables, lo que las hacen interesantes para diferentes aplicaciones como la construcción integrada y la agrovoltaica. Para estas aplicaciones, el ángulo de incidencia de la luz viene dado por limitaciones estructurales y, por tanto, es importante entender qué controla la dependencia del rendimiento de las células solares según el ángulo de incidencia de la luz. Aquí se mide la dependencia angular de una célula solar orgánica para cuantificar los efectos de la reducción de la intensidad de la luz, del aumento del camino óptico dentro de la capa activa y de la variación angular de las pérdidas de reflexión ., Les cèl·lules solars orgàniques capten l'atenció pel fet de ser lleugeres, de baix cost i de tenir propietats òptiques ajustables, cosa que les fan interessants per a diferents aplicacions com la construcció integrada i l'agrovoltaica. Per a aquestes aplicacions, l'angle d'incidència de la llum ve donat per limitacions estructurals i, per tant, és important entendre què controla la dependència del rendiment de les cèl·lules solars segons l'angle d'incidència de la llum. Aquí es mesura la dependència angular d'una cèl·lula solar orgànica per quantificar els efectes de la reducció de la intensitat de la llum, de l'augment del camí òptic dins de la capa activa i de la variació angular de les pèrdues de reflexió.

The main limiting factor of kesterite-related solar cells is the low open-circuit voltage (VOC) relative to their bandgap. This drawback has been correlated with the easily formed anti-site defects caused by similar ionic radii and/or chemical valence. Recent success in suppressing Sn-related defects by using Cd to replace Zn in Cu2CdSnS4 was attributed to the higher formation energy of the 2CuCd + SnCd defect complex compared to its counterpart in Cu2ZnSnS4. This has motivated the use of bigger ions to replace Cu in Cu2CdSnS4 to reduce the possibilities of III and III defect formation. In this work, we substitute Cu in Cu2CdSnS4 with larger Ag at various concentrations and investigate the structural, optoelectronic, and photovoltaic properties of (Cu,Ag)2CdSnS4. Higher concentrations of Ag lead to peak splitting in XRD spectra, which is attributed to mixed phases and marks the transition towards Ag2CdSnS4. This is also complemented by Raman scattering analysis, the first time the Raman spectrum of Ag2CdSnS4 is reported. Doping type inversion was observed for pure n-type Ag2CdSnS4 instead of the p-type of Cu2CdSnS4, accompanied by high carrier mobility and sharp absorption onset. Further optoelectronic and photovoltaic characterization reveals that adding 5% Ag concentration improves Cu2CdSnS4 device performance to 7.72%, mainly due to superior film quality and improved interface properties. As a result, better carrier collection contributes to the short-circuit current improvement of the champion device., Peer Reviewed, Postprint (published version)

In this article, a communication platform for a self-powered integrated light energy harvester based on a wireless hybrid transceiver is proposed. It consists of an optical receiver and a reconfigurable radio frequency (RF) transmitter. The hybrid optical/RF communication approach improves load balancing, energy efficiency, security, and interference reduction. A light beam for communication in the downlink, coupled with a 1 MHz radio frequency signal for the uplink, offers a small area and ultra-low-power consumption design for Smart Dust/IoT applications. The optical receiver employs a new charge-pump-based technique for the automatic acquisition of a reference voltage, enabling compensation for comparator offset errors and variations in DC-level illumination. On the uplink side, the reconfigurable transmitter supports OOK/FSK/BPSK data modulation. Electronic components and the energy harvester, including integrated photodiodes, have been designed, fabricated, and experimentally tested in a 0.18 µm triple-well CMOS technology in a 1.5 × 1.3 mm2 chip area. Experiments show the correct system behavior for general and pseudo-random stream input data, with a minimum pulse width of 50 µs and a data transmission rate of 20 kb/s for the optical receiver and 1 MHz carrier frequency. The maximum measured power of the signal received from the transmitter is approximately -18.65 dBm when using a light-harvested power supply., Postprint (published version)

The purpose of this project is to study the impact of shared micro-mobility on the environment and the development of advanced solutions to reduce the environmental impacts of shared micro-mobility. This project consists of the design and development of a solar energy harvesting system for powering an e-scooter used in a shared micro-mobility MaaS., El propósito de este proyecto es estudiar el impacto de la micromovilidad compartida en el medio ambiente y el desarrollo de soluciones avanzadas para reducir los impactos ambientales de la micromovilidad compartida. Este proyecto consiste en el diseño y desarrollo de un sistema de captación de energía solar para alimentar un e-scooter utilizado en un MaaS de micromovilidad compartida., L'objectiu d'aquest projecte és estudiar l'impacte de la micro-mobilitat compartida en el medi ambient i el desenvolupament de solucions avançades per reduir els impactes ambientals de la micro-mobilitat compartida. Aquest projecte consisteix en el disseny i desenvolupament d'un sistema de captació d'energia solar per alimentar un scooter elèctric utilitzat en un MaaS de micro-mobilitat compartit.

Semitransparent solar cells are very attractive due to the increasing integration in daily life. Kesterite-type based thin-film solar cells stand out because of its environmentally benign composition and outstanding stability. Herein, the influence of the back contact (Mo/V2O5/FTO or Mo/FTO) and thickness of Cu2ZnGe(S,Se)4 (CZGSSe) absorber layer, grown by sulfurization of coevaporated CZGSe, is investigated. To increase the transparency, thinner absorber layers with higher bandgap energy are produced. A double sulfur gradient through the CZGSSe layer with a considerable S content near the back contact and the formation of Mo(S,Se)2 phase at the back interface is detected for an absorber of only 400¿nm thickness. Efficiencies of 3.1% and 2.7% are achieved for 1.2¿µm CZGSSe-based devices with Eg of 1.73 and 1.86¿eV, respectively, while enabling transmittance values higher than 20% in the near-infrared (NIR). The highest transmittance, 40% in the NIR, is achieved for the 400¿nm CZGSSe-based solar cells with Eg of 2.1¿eV; however, a significant reduction of these devices’ performance is obtained due to the presence of ZnS secondary phase and a different back-contact interface formation. This work presents the first promising semitransparent CZGSSe solar cells, opening new paths of applications., Peer Reviewed, Postprint (published version)

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Appl. Mater. Interfaces, copyright © 2023 after peer review and technical editing by the publisher. To access the final edited and published work seehttps://pubs.acs.org/doi/10.1021/acsami.3c10336., A hierarchical cobalt carbonate hydroxide (CCH) nanostructure with outstanding electrochemical kinetics and structural stability for energy storage is largely unknown. Herein, we report tin oxide-functionalized CCH surface-enabled unique two-dimensional (2D) interlayered heterostructures that promote high conductivity with more electroactive sites to maximize redox reactions. A simple electrodeposition technique was utilized to construct the hierarchical 2D CCH electrode, while a surface-reinforced method was employed to fabricate the 2D interlayered SnO on CCH. The fabricated SnO@CCH-8 electrode showed a maximum areal capacity of 720 mC cm–2 (specific capacitance of 515 F g–1) at a current density of 1 mA cm–2 in 3 M KOH electrolyte. The obtained results indicate that the synergetic effect of SnO in the CCH network delivers an efficient charge transfer pathway to achieve high-performance energy storage. Moreover, SnO@CCH-8//AC was devised as a hybrid supercapacitor (HSC), ensuring a maximum specific capacitance of 129 F g–1 and maximum specific energy and power of 40.25 W h kg–1 and 9000 W kg–1, respectively, with better capacitance retention (94%) even beyond 10,000 cycles. To highlight the excellent performance in real-time studies, the HSC was constructed using a coin cell and displayed to power 21 light-emitting diodes (LEDs)., Peer Reviewed, Postprint (author's final draft)

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The journal of physical chemistry letters, copyright © 2023 The Authors. Published by American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/full/10.1021/acs.jpclett.3c00643, Poly(amidoamine) (PAMAM) dendrimers are used to modify the interface of metal-semiconductor junctions. The large number of protonated amines contributes to the formation of a dipole layer, which finally serves to form electron-selective contacts in silicon heterojunction solar cells. By modification of the work function of the contacts, the addition of the PAMAM dendrimer interlayer quenches Fermi level pinning, thus creating an ohmic contact between the metal and the semiconductor. This is supported by the observation of a low contact resistivity of 4.5 mO cm2 , the shift in work function, and the n-type behavior of PAMAM dendrimer films on the surface of crystalline silicon. A silicon heterojunction solar cell containing the PAMAM dendrimer interlayer is presented, which achieved a power conversion efficiency of 14.5%, an increase of 8.3% over the reference device without the dipole interlayer., This research has been supported by the Spanish government through Grants PID2019-109215RB-C41, PID2019- 109215RB-C43, and PID2020-116719RB-C41 funded by MCIN/AEI/10.13039/501100011033. Thomas Tom acknowledges the support of the Secretaria d’Universitats i Recerca de la Generalitat de Catalunya and the European Social Fund (2019 FI_B 00456). In addition, the authors thank the technical staff from Barcelona Research Center in Multiscale Science and Engineering from the Universitat Politecnica ̀ de Catalunya for their expertise and helpful discussions over the XPS results, Dr. Oriol Arteaga from the Universitat de Barcelona for the ellipsometry measurements, and Guillaume Sauthier from the Catalan Institute of Nanoscience and Nanotechnology for his contribution to UPS measurements and their discussion., Peer Reviewed, Postprint (published version)

Van der Waals chalcogenides and chalcohalides have the potential to become the next thin film PV breakthrough, owing to the earth-abundancy and non-toxicity of their components, and their stability, high absorption coefficient and quasi-1D structure, which leads to enhanced electrical anisotropic properties when the material is oriented in a specific crystalline direction. However, quasi-1D semiconductors beyond Sb2(S,Se)3, such as SbSeX chalcohalides, have been scarcely investigated for energy generation applications, and rarely synthesised by physical vapor deposition methodologies, despite holding the promise of widening the bandgap range (opening the door to tandem or semi-transparent devices), and showing enticing new properties such as ferroelectric behaviour and defect-tolerant nature. In this work, SbSeI and SbSeBr micro-columnar solar cells have been obtained for the first time by an innovative methodology based on the selective halogenation of Sb2Se3 thin films at pressure above 1 atm. It is shown that by increasing the annealing temperature and pressure, the height and density of the micro-columnar structures grows monotonically, resulting in SbSeI single-crystal columns up to 30 µm, and tuneable morphology. In addition, solar cell prototypes with substrate configuration have shown remarkable Voc values above 550 mV and 1.8 eV bandgap., Peer Reviewed, Postprint (published version)

In order to make better use of clean energy such as solar energy, textile on earth have the potential to be made into solar textiles. The commercial solar cells can be embedded between the textile layers by laminating to harvest energy for e-textile applications. Research about solar textiles is not mature enough, and many aspects of the problem need to be solved. However, connecting techniques of conductive textile wires to flexible and solid solar cells are not in-deep studied. In addition, solar textile products with these connection technologies must meet washable requirements. To solve the problem of connecting textile wires to flexible and solid solar cells in the production of solar textiles, this study proposes three connection techniques for solar textiles, which are tape, adhesive and stitching based on literature and experimental validation. The feasibility of tape and adhesive methods was analyzed by literature review and the feasibility of stitching method was verified by experiments. The stitching is unapplicable method for solid solar cells that are difficult to penetrate, but applicable for flexible solar cells. The machine-washing durability of solar textile which composed of solar cells with stitch-connected conductive textile wires was verified by experiments. First, the textile wires were joined to flexible solar cells by stitching with the sewing machine and then embedded between fabric layers with TPU-lamination to simulate real set up in e-textile application. The humidity stickers were attached to the surface of solar cells, and it was expected to present solar textile samples with or without water inside. After the machine-washing process is completed, the individual parts of the solar textile sample are disassembled by delamination. For stitching method, after 15 machine wash tests by household washing machines, the performance of the solar cells was hardly affected, and the internal water resistance of the samples was good. The delaminatio

© 2023 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., In this article, we study the effect of the inversion charge ( Q inv ) in a solar cell based on the hole-selective characteristic of substoichiometric molybdenum oxide (MoO x ) and vanadium oxide (VO x ) deposited directly on n-type silicon. We measure the capacitance–voltage ( C – V ) curves of the solar cells at different frequencies and explain the results taking into account the variation of the space charge and the existence of Q inv in the c-Si inverted region. The high-frequency capacitance measurements follow the Schottky metal–semiconductor theory, pointing to a low inversion charge influence in these measurements. However, for frequencies lower than 20 kHz, an increase in the capacitance is observed, which we relate to the contribution of the inversion charge. In addition, applying the metal–semiconductor theory to the high-frequency measurements, we have obtained the built-in voltage potential and show new evidence about the nature of the conduction process in this structure. This article provides a better understanding of the transition metal oxide/n-type crystalline silicon heterocontact., The authors would like to acknowledge the CAI de Técnicas Físicas of the Universidad Complutense de Madrid. The authors would also like to thank the Mexican grants program CONACyT for its financial collaboration., Peer Reviewed, Postprint (author's final draft)

This is the peer reviewed version of the following article: Lopez-Garcia, A. [et al.]. Ultrathin a-Si:H/Oxide transparent solar cells exhibiting UV-Blue selective-like absorption. "Solar RRL", April 2023, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/solr.202200928. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited., Herein, the fabrication of transparent solar cells based on nanometric (8 and30 nm) intrinsic hydrogenated amorphous siliconfilms (a-Si:H) and using oxidethinfilms as transparent carrier selective contacts are reported. The ultrathindevices present photovoltaic effect and high average visible transmittance (AVT).Additionally, they display a shifted spectral response toward short wavelengths.Glass/fluorine-doped tin oxide (FTO)/aluminum-doped zinc oxide (AZO)/a-Si:H/MoO3/indium tin oxide (ITO) prototypes are shown, presenting AVT=35% andphotovoltaic conversion efficiency (PCE)=2% for a device with a 30 nm a-Si:Hfilm. This yields a light utilization efficiency (LUE) of 0.7%, a record up to this datefor inorganic oxide-based transparent solar cells. For devices including an 8 nma-Si:Hfilm, the AVT reaches 66% with a PCE=0.6% (LUE=0.4%). These highAVT values are comparable or even superior in some cases to those achieved forpure oxide devices. Thesefindings confirm the potential of the proposedarchitectures for the development of highly transparent energy harvesters asfunctional components in building-integrated photovoltaics (BIPV), agrophoto-voltaics (APV), sensors and other low-power devices. In addition, these devicesare fabricated with earth-abundant materials and with up-scalable techniquesthat can allow for a feasible implementation., Peer Reviewed, Postprint (published version)

High open-circuit voltage in Sb2Se3 thin-film solar cells is a key challenge in the development of earth-abundant photovoltaic devices. CdS selective layers have been used as the standard electron contact in this technology. Long-term scalability issues due to cadmium toxicity and environmental impact are of great concern. In this study, we propose a ZnO-based buffer layer with a polymer-film-modified top interface to replace CdS in Sb2Se3 photovoltaic devices. The branched polyethylenimine layer at the ZnO and transparent electrode interface enhanced the performance of Sb2Se3 solar cells. An important increase in open-circuit voltage from 243 mV to 344 mV and a maximum efficiency of 2.4% was achieved. This study attempts to establish a relation between the use of conjugated polyelectrolyte thin films in chalcogenide photovoltaics and the resulting device improvements., This research was supported by the Spanish government through grants PID2019-109215RB-C41, PID2019-109215RB-C43, and PID2020-116719RB-C41 funded by MCIN/AEI/10.13039/501100011033. This research was funded by the European Union H2020 Framework Programme under Grant Agreement No. 866018, low-dimensional semiconductors for optically tunable solar harvesters (SENSATE). E.S. acknowledges the ICREA Academia program. One of the authors (T.T.) acknowledges the support of the Secretaria d’Universitats i Recerca de la Generalitat de Catalunya and European Social Fund (2019 FI_B 00456)., Peer Reviewed, Postprint (published version)

In this work, a new design of transparent conductive electrode based on a graphene monolayer is evaluated. This hybrid electrode is incorporated into non-standard, high-efficiency crystalline silicon solar cells, where the conventional emitter is replaced by a MoOx selective contact. The device characterization reveals a clear electrical improvement when the graphene monolayer is placed as part of the electrode. The current–voltage characteristic of the solar cell with graphene shows an improved FF and Voc provided by the front electrode modification. Improved conductance values up to 5.5 mS are achieved for the graphene-based electrode, in comparison with 3 mS for bare ITO. In addition, the device efficiency improves by around 1.6% when graphene is incorporated on top. These results so far open the possibility of noticeably improving the contact technology of non-conventional photovoltaic technologies and further enhancing their performance., This research was funded by MCIN/AEI/10.13039/501100011033, grant numbers PID2019-109215RB-C41 and PID2019-109215RB-C42., Peer Reviewed, Postprint (published version)

The thermal stability of the Cu2ZnSnSe4 (CZTSe) absorber and CdS buffer layers in SLG/Mo/CZTSe/CdS/i-ZnO/ITO devices is explored by performing a series of soft (~200 °C) post deposition treatments (PDTs). A comprehensive analysis of a sample comprised by 56 individual devices by means of Raman and photoluminescence spectroscopies coupled with optoelectronic characterization is performed at different PDT steps. This allows isolating the effects of the PDT on the CZTSe absorber and CdS buffer layer separately and reveals clear evidences of: i) a degradation of the absorber due to Cu/Zn disorder that hinders device performance, and ii) an improvement of the buffer layer by the recrystallization of the CdS nanolayer that is the main responsible for the PDT-induced efficiency improvement. As such, it is concluded that CZTSe/CdS based PV devices present a low thermal stability under relatively low temperatures (in the 100–200 °C range), comparable to the temperatures employed at the final production stages of thin film PV devices or even during device operation, that leads to significant changes in solar cell performance and needs to be taken into consideration for the further development of the kesterite PV technology. These results are supported by a novel methodology for easily discerning between changes in Cu/Zn disorder and in point defects concentration in kesterites based on solely on Raman spectroscopy that is proposed in this work and developed through the analysis of a set of CZTSe powder samples with strong variation of the order parameter Q., Postprint (published version)

This is the peer reviewed version of the following article: Tom, T. [et al.]. Deoxyribonucleic acid-based electron selective contact for crystalline silicon solar cells. "Advanced materials technologies (Weinheim)" [en línia], 10 Febrer 2023, [Consulta: 12 Desembre 2022]. Disponible a: http://hdl.handle.net/2117/377832, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/admt.202200936. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited., Development of carrier selective contacts for crystalline silicon solar cells has been recently of great interest toward the further expansion of silicon photovoltaics. The use of new electron and hole selective layers has opened an array of possibilities due to the low-cost processing and non-doping contacts. Here, a non-doped heterojunction silicon solar cell without the use of any intrinsic amorphous silicon is fabricated using Deoxyribonucleic acid (DNA) as the electron transport layer (ETL) and transition metal oxide V2O5 as the hole transport layer (HTL). The deposition and characterization of the DNA films on crystalline silicon have been studied, the films have shown a n-type behavior with a work function of 3.42 eV and a contact resistance of 28 mO cm2. This non-doped architecture has demonstrated a power conversion efficiency of 15.6%, which supposes an increase of more than 9% with respect to the cell not containing the biomolecule, thus paving the way for a future role of nucleic acids as ETLs., T.T. and E.R. shared co-first authorship. This research was supported by Spanish government through grants PID2019-109215RB-C41, PID2019-109215RB-C43, and PID2020-116719RB-C41 funded by MCIN/ AEI/10.13039/501100011033. One of the authors (T.T.) acknowledges the support of the Secretaria d’Universitats i Recerca de la Generalitat de Catalunya and European Social Fund (2019 FI_B 00456). Besides this, the authors thank technical staff from Barcelona Research Center in Multiscale Science and Engineering from Universitat Politècnica de Catalunya for its expertise and helpful discussions over XPS results, Dr. Oriol Arteaga Barriel from Universitat de Barcelona for the thickness measurements, and also Guillaume Sauthier from Catalan Institute of Nanoscience and Nanotechnology for his contribution through UPS measurements and discussions., Peer Reviewed, Postprint (published version)

Commercial solar cells can be embedded between textile layers by laminating to harvest energy in e-textile applications. However, techniques for connecting conductive textile wires to flexible and solid solar cells have not been studied in depth. Based on the literature and experimental validation, this study proposes a stitching connection technique for solar textiles. The feasibility of stitching was experimentally validated. First, the textile wires were joined to flexible solar cells by stitching with a sewing machine, and then embedded between fabric layers with TPU-lamination to simulate a real set-up in e-textile application. The machine washing durability of textile solar cell components with stitch-connected conductive textile wires was successfully verified, Acknowledgments: The authors acknowledge the support of Department de Recerca i Universitats de la Generalitat de Catalunya to the textile research group TECTEX (2021SGR01056), Postprint (published version)

Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27¿mA¿cm-2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions., G.K. acknowledges financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 725165), the Fundació Joan Ribas Araquistain (FJRA), the Fundació Privada Cellex, the program CERCA, EQC2019-005797-P (AEI/FEDER UE), 2017SGR1373 and ‘Severo Ochoa’ Centre of Excellence CEX2019-000910-S funded by the Spanish State Research Agency. Y.W. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 754558. I.B.-C. acknowledges support from the Government of Catalonia’s Beatriu de Pinós postdoctoral programme (grant no. 2017BP00241). S.R.K. thanks L. Harnett-Caulfield for help with using the alloy theoretic automated toolkit software package and Y.-S. Choi for help with calculating the Madelung potentials; he also acknowledges the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials (CDT-ACM) (EP/S023259/1) for funding a PhD studentship. A.W. and D.O.S. acknowledge the use of the UCL Kathleen High Performance Computing Facility (Kathleen@UCL), the Imperial College Research Computing Service and associated support services. By the membership of the UK’s HEC Materials Chemistry Consortium, which is funded by the EPSRC (EP/L000202, EP/R029431 and EP/T022213), this work used the ARCHER2 UK National Supercomputing Service and the UK Materials and Molecular Modelling (MMM) Hub (Thomas EP/P020194 and Young EP/T022213). D.O.S. acknowledges support from the EPSRC (EP/N01572X/1) and the European Research Council, ERC (grant no. 758345)., Peer Reviewed, Postprint (author's final draft)

Strong optical absorption by a semiconductor is a highly desirable property for many optoelectronic and photovoltaic applications. The optimal thickness of a semiconductor absorber is primarily determined by its absorption coefficient. To date, this parameter has been considered as a fundamental material property, and efforts to realize thinner photovoltaics have relied on light-trapping structures that add complexity and cost. Here we demonstrate that engineering cation disorder in a ternary chalcogenide semiconductor leads to considerable absorption increase due to enhancement of the optical transition matrix elements. We show that cation-disorder-engineered AgBiS2 colloidal nanocrystals offer an absorption coefficient that is higher than other photovoltaic materials, enabling highly efficient extremely thin absorber photovoltaic devices. We report solution-processed, environmentally friendly, 30-nm-thick solar cells with short-circuit current density of 27 mA cm−2, a power conversion efficiency of 9.17% (8.85% certified) and high stability under ambient conditions., Peer Reviewed, Postprint (author's final draft)

Els MXens, una classe de carburs, nitrurs i carbonitrurs bidimensionals, tenen conductivitat metàl·lica, alta mobilitat del portador, una funció de treball ajustable i transparència; això en fa una tecnologia atractiva per utilitzar com elèctrodes, capes de transport d'orificis o additius en dispositius fotovoltaics de pel·lícula prima. Aquest treball conté el modelatge matemàtic, el desenvolupament d'algorismes i l'optimització del procés de deposició per esprai d'una capa homogènia de Ti3C2Tx MXenes. La implementació d'un sistema de deposició de capes gradualment desviades va reduir l'error de gruix de la pel·lícula en un 83%. El seleniur d'antimoni (III) (Sb2Se3) és un calcogenur d'antimoni inorgànic la relativa abundància, baixa toxicitat i excel·lents característiques electroquímiques del qual en fan un candidat adequat com a absorbent en cèl·lules solars de pel·lícula fina. El Sb2Se3 té una eficiència experimental màxima significativament inferior al màxim teòric, atribuït en gran mesura a les pèrdues en l'extracció del portador i en l'orientació cristal·lina. L'ús d'un MXene com a capa de transport d'elèctrodes/forats pot mitigar aquestes pèrdues. El procés de deposició per esprai desenvolupat en aquest treball es va utilitzar per dipositar MXenes amb un gruix de pel·lícula variable sobre elèctrodes de Mo/ITO/FTO; les piles d'elèctrodes completades es van utilitzar posteriorment en la fabricació de cèl·lules solars Sb2Se3/CdS. L'espectroscòpia Raman i XRD van mostrar pel·lícules de MXene completament desenvolupades, amb bona estructura i lleugeres millores en la resistència de la làmina; els absorbents de Sb2Se3 van mostrar signes de presència de Se trigonal i amorf. L'anàlisi J-V realitzada sobre les cèl·lules solars va mostrar una eficiència i valors factor de forma (FF) moderats en comparació amb un elèctrode de Mo de referència, encara que els valors màxims mesurats indiquen el potencial de MXene després d'una optimització futura addicional., Los MXenes, una clase de carburos, nitruros y carbonitruros bidimensionales, tienen conductividad metálica, alta movilidad del portador, una función de trabajo ajustable y transparencia; esto hace de ellos una tecnología atractiva para usar como electrodos, capas de transporte de orificios o aditivos en dispositivos fotovoltaicos de película delgada. Este trabajo contiene el modelado matemático, el desarrollo de algoritmos y la optimización del proceso de deposición por spray de una capa homogénea de Ti3C2Tx MXenes. La implementación de un sistema de deposición de capas gradualmente desviadas redujo el error de espesor de la película en un 83%. El seleniuro de antimonio (III) (Sb2Se3) es un calcogenuro de antimonio inorgánico cuya relativa abundancia, baja toxicidad y excelentes características electroquímicas hacen de él un candidato adecuado como absorbente en células solares de película fina. El Sb2Se3 tiene una eficiencia experimental máxima significativamente inferior a su máximo teórico, atribuido en gran medida a las pérdidas en la extracción del portador y en la orientación cristalina. El uso de un MXene como capa de transporte de electrodos/agujeros puede mitigar estas pérdidas. El proceso de deposición por spray desarrollado en este trabajo se utilizó para depositar MXenes con un espesor de película variable sobre electrodos de Mo/ITO/FTO; las pilas de electrodos completadas se utilizaron posteriormente en la fabricación de células solares Sb2Se3/CdS. La espectroscopia Raman y XRD mostraron películas de MXene completamente desarrolladas, con buena estructura y ligeras mejoras en la resistencia de la lámina; los absorbentes de Sb2Se3 mostraron signos de presencia de Se trigonal y amorfo. El análisis J-V realizado sobre las células solares mostró una eficiencia y valores factor de forma (FF) moderados en comparación con un electrodo de Mo de referencia, aunque los valores máximos medidos indican el potencial de MXene tras una optimización futura adicional., MXenes, a class of two-dimensional carbides, nitrides, and carbonitrides, have metallic conductivity, high carrier mobility, a tunable work function, and transparency, making them an appealing technology for use as electrodes, hole transport layers, or additives in thin film photovoltaic devices. In this work, mathematical modelling, algorithm development, and optimization is conducted for the spray deposition of a homogeneous layer of Ti3C2Tx MXenes. The implementation of a systematic layer offset decreased film thickness error by 83%. Antimony(III) selenide (Sb2Se3) is an inorganic, relatively abundant, and low-toxicity antimony chalcogenide with excellent electrochemical characteristics, making it a suitable candidate for absorbers in thin film solar cells. Sb2Se3 has a maximum experimental efficiency significantly below its theoretical maximum, largely attributed to losses in carrier extraction and crystalline orientation. The use of a MXene as an electrode/hole transport layer may mitigate these losses. The spray deposition process developed in this work was used to deposit MXenes with varying film thickness atop Mo/ITO/FTO electrodes; completed electrode stacks were subsequently fabricated into Sb2Se3/CdS solar cells. Raman spectroscopy and XRD found fully developed MXene films with good structure and slight improvements in sheet resistance, and the Sb2Se3 absorbers showed signs of trigonal and amorphous Se presence. J-V analysis conducted on completed devices yielded only moderate efficiency and fill factor (FF) values when compared to a reference Mo electrode, though peak measured values indicate the potential of MXene with additional future optimization.

2D materials emerge with a promising future for optoelectronics. First reported in 2011, MXenes have excellent properties such as metallic-like conductivity and high transmittance, thus, they can be used as transparent electrodes. MXenes also posses a tunable work function that depends on the termination radicals on its surface. Their ability to extract charge carriers and act as selective contacts has also been reported, although barely in contact with silicon. In this work, buffer layers consisting of dipoles will help improving the contact with silicon, varying the work function of MXene, improving wettability and determining what type of selective contact MXene can be., Los materiales 2D surgen con un futuro prometedor para la optoelectrónica. Mencionados por primera vez en el año 2011, los MXenes tienen excelentes propiedades, como una conductividad similar a un metal y una alta transmitancia, por tanto, se pueden utilizar como electrodos transparentes. Los MXenes también tienen una función de trabajo ajustable que depende de los radicales de terminación de su superficie. También se ha informado de su capacidad para extraer portadores de carga y actuar como contactos selectivos, aunque apenas en contacto con silicio. En este trabajo, capas amortiguadoras formadas por dipolos ayudarán a mejorar el contacto con el silicio, variar la función de trabajo del MXene, mejorar la mojabilidad y determinar qué tipo de contacto selectivo puede ser el MXene., Els materials 2D sorgeixen amb un futur prometedor per a l'optoelectrònica. Mencionats per primera vegada l'any 2011, els MXenes tenen excel·lents propietats, com ara una conductivitat semblant a un metall i una alta transmitància, per tant, es poden utilitzar com a elèctrodes transparents. Els MXenes també tenen una funció de treball ajustable que depèn dels radicals de terminació de la seva superfície. També s'ha informat de la seva capacitat per extreure portadors de càrrega i actuar com a contactes selectius, encara que amb prou feines en contacte amb silici. En aquest treball, capes amortidores formades per dipols ajudaran a millorar el contacte amb el silici, variar la funció de treball de l'MXene, millorar la mullabilitat i determinar quin tipus de contacte selectiu pot ser l'MXene.

According to intermediate band (IB) theory, it is possible to increase the efficiency of a solar cell by boosting its ability to absorb low-energy photons. In this study, we used a hyperdoped semiconductor approach for this theory to create a proof of concept of different silicon-based IB solar cells. Preliminary results show an increase in the external quantum efficiency (EQE) in the silicon sub-bandgap region. This result points to sub-bandgap absorption in silicon having not only a direct application in solar cells but also in other areas such as infrared photodetectors. To establish the transport mechanisms in the hyperdoped semiconductors within a solar cell, we measured the J–V characteristic at different temperatures. We carried out the measurements in both dark and illuminated conditions. To explain the behavior of the measurements, we proposed a new model with three elements for the IB solar cell. This model is similar to the classic two-diodes solar cell model but it is necessary to include a new limiting current element in series with one of the diodes. The proposed model is also compatible with an impurity band formation within silicon bandgap. At high temperatures, the distance between the IB and the n-type amorphous silicon conduction band is close enough and both bands are contacted. As the temperature decreases, the distance between the bands increases and therefore this process becomes more limiting., The authors would like to thank the Physical Sciences Research Assistance Centre (CAI de Técnicas Físicas) of the Complutense University of Madrid. This study was partially funded by Project MADRID-PV2 (P2018/EMT-4308), with aid from the Regional Government of Madrid and the ERDF, by the Spanish Ministry of Science and Innovation/National Research Agency (MCIN/AEI) under grants TEC2017- 84378-R, PID2019-109215RB-C41, PID2020-116508RB-I00 and PID2020- 117498RB-I00. Daniel Caudevilla would like to express his thanks for grant PRE2018-083798, provided by the MICINN and the European Social Fund. Francisco Pérez Zenteno would also like to express his thanks for grant 984933, provided by CONACyT (Mexico)., Peer Reviewed, Postprint (author's final draft)

This is the peer reviewed version of the following article: Lopez-Garcia, A. [et al.]. Ultrathin wide-bandgap a-Si:H-based solar cells for transparent photovoltaic applications. "Solar RRL", 1 Gener 2022, vol. 6, núm. 1, p. 2100909:1-2100909:8. , which has been published in final form at https://onlinelibrary.wiley.com/doi/full/10.1002/solr.202100909. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving., Herein, the fabrication of UV-blue selective transparent solar cells based on ultrathin (<30¿nm) intrinsic hydrogenated amorphous silicon films (a-Si:H) as absorber and using a fully inorganic architecture is reported, using metal-oxide thin films as carrier selective contacts and as transparent electrical contacts. These transparent ultrathin devices present a photovoltaic effect and high average visible transmittance (AVT), showing their potential as candidates for implementation as a transparent energy harvester. Potential applications range from Building-Integrated PV to agrophotovoltaics, and can also be of interest as a ubiquitous and inexpensive power source integrated in functional devices such as low-power devices, Internet of Things devices, and other sensors. Glass/FTO/ZnO/a-Si:H/MoO3/ITO device prototypes are produced. These devices present an AVT ranging from 50% to 69%, present a photovoltaic effect with a power conversion efficiency up to 0.5% calculated for an AM1.5G spectrum and have light utilization efficiency (LUE) values of 0.25%, confirming the potential of the proposed device architectures for the development of highly transparent devices with improved LUE., This work has received funding from the European Union H2020Framework Programme under Grant Agreement no. 826002(Tech4Win). This work is also part of the RþDþi MaterOne projects(Refs. PID 2020-116719RB-C42 and PID 2020-116719RB-C41) and ofthe RþDþi SCALED project (Ref. PID 2019-109215RB-C4) funded byMCIN/AEI/10.13039/5011000110033. Authors from IREC andUniversitat de Barcelona belong to the SEMS (Solar Energy Materialsand Systems) Consolidated Research Group of the“Generalitat deCatalunya”(Ref. 2017 SGR 862)., Peer Reviewed, Postprint (published version)

Kesterite, or Cu2ZnSn(S,Se)4 (CZTS) is promising in developing sustainable PV technology due to its earth-abundant, non-toxic composition. However, issues including instability of interface, high density of defects that fails to allow the short charge-collection length to meet its light absorption needs, use of Cd that fails to comply with the restriction of hazardous substances (RoSH), are promoting the development of alternative, eco-friendly device structure. Here, this study reports an important progress on this subject by adopting the superstrate configuration to kesterite, thus to realize advantageous light management and high defect tolerance in an ultrathin device. By incorporating Ag in kesterite to overcome the detrimental alignment at the pristine interface, a solar cell with PCE of 8.1% has been fabricated with ~ 200 nm absorber and ~ 15 nm TiO2 buffer, representing a PCE improvement of nearly three-fold from the baseline Cu2ZnSn(S,Se)4 device and breaking the 5% PCE limit for superstrate kesterite cells to date. Moreover, this enables the sole use of TiO2 as novel buffer material free of toxic Cd. Further analysis reveals the critical role of Ag in synergistically tailoring band offset and bandgap, along with largely reduced density of defects, leading to this substantial performance improvement., Peer Reviewed, Postprint (published version)

© 2022 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, In this paper, we present a study of the laser scribing of WOx, VOx, and MoOx films, deposited onto crystalline silicon, with three different wavelengths (355 nm, 532 nm, and 1064 nm) and in two temporal regimes in pulse width, picosecond and nanosecond. For each case, we measure the fluence threshold to remove the transition metal oxides (TMO) film and the fluence threshold to induce damage in the crystalline silicon substrate. The relation between the process parameters and the morphological changes produced in the oxide films is also analysed. The selection of the proper laser source allows a wide parametric window, leading to the complete removal of the TMO films without alteration of the crystalline silicon substrate. Morphological changes of the ablated regions were characterized through confocal microscopy and the relationships between the dimensions of the craters and the ablation parameters were analysed. Finally, we present results on the isolation of diodes and their electrical characteristics, showing the quality of the laser scribing processes., Partial financial support for this work has been provided by the Spanish Ministry of Science and Innovation under the projects CHENOC (ENE2016–78933-C4–1-R and ENE2016–78933-C4–4-R) and SCALED (PID2019–109215RB-C41 and PID2019–109215RB-C44)., Peer Reviewed, Postprint (author's final draft)

Silver bismuth sulfide nanocrystals (AgBiS2 NCs) are emerging absorber materials for low-cost solar cells, owing to their solution-processability, environmentally friendliness, earth abundance, and high absorption coefficients. When it comes to green manufacturing technologies, besides the semiconductor materials, solvents play an equally important role. Here, solution-phase ligand-exchanged (SPLE) AgBiS2 nanocrystal inks employing 3-mercaptopropionic (MPA) in methanol as a ligand solution are introduced. The resultant MPA capped AgBiS2 nanocrystals can be fully dissolved in water, forming completely environmentally friendly nanocrystal inks. These nanocrystal inks allow the fabrication of fully green-processed photovoltaic devices with a power conversion efficiency up to 7.3%. This method not only demonstrates the potential of solution-phase ligand-exchanged AgBiS2 nanocrystal inks, but also paves a path toward fully green-processed nanocrystal devices., The authors acknowledge financial support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 725165) and the Fundació Joan Ribas Araquistain (FJRA). This project was supported also by Fundació Privada Cellex, the program CERCA, EQC2019-005797-P (AEI/FEDER UE), 2017SGR1373 and “Severo ochoa” Center of Excellence CEX2019-000910-S – Funded by the Spanish State Research Agency. Y.W. acknowledges the support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 754558. Z.W. acknowledges the support from the Marie Sklodowska-Curie Individual Fellowship (SUSNASOL, grant agreement No. 886953)., Peer Reviewed, Postprint (author's final draft)

UPC NanoSat Lab is a laboratory located in the Universitat Politècnica de Catalunya, which is focused on the design and development of nano and picosatellite spacecrafts. This type of platforms have significant limitations in dimensions and structure. Nevertheless, due to its reduced cost, there is a high momentum as many companies and universities are investing their resources in innovative applications for Earth observation and communications. This thesis is part of a UPC NanoSat Lab project for the IEEE Geoscience and Remote Sensing Society called "Open PocketQube Kit". It aims at developing different educational PocketQubes, a type of picosatellite with a 5 cm cube size, which will be integrated in the 3Cat-8 mission. Precisely, this final degree thesis is focused on the design and implementation of the electrical power supply for these spacecrafts as well as a thermal analysis study for the whole of the structure., El UPC NanoSat Lab es un laboratorio de la Universidad Politécnica de Cataluña, que se centra en el diseño y desarrollo de nano y picosatélites. Este tipo de plataformes tienen limitaciones significativas en dimensiones y potencia. Sin embargo, debido a su coste reducido, existe un impulso creciente por parte de muchas empresas y universidades que estan invirtiendo sus recursos en aplicaciones innovadoras de observación terrestre y comunicaciones. Este trabajo de final de grado forma parte de un proyecto del UPC NanoSat Lab para la IEEE Geoscience and Remote Sensing Society titulado "Open PocketQube Kit" que tiene como objectivo desarrollar diferentes PocketQubes educativos, un tipo de picosatélites con forma de cubo de 5 cm de tamaño, los cuales irán integrados dentro de la misión del 3Cat-8. Precisamente, este trabajo de final de grado está centrado en el diseño e implementación del subsistema de alimentación eléctrica de estas plataformas así como un análisis térmico del conjunto de toda la misión., L'UPC NanoSat Lab és un laboratori de la Universitat Politècnica de Catalunya, focalitzat en el disseny i desenvolupament de nano i picosatèl·lits. Aquest tipus de plataformes tenen limitacions significatives en dimensions i potència. Tanmateix, degut al seu reduït cost, existeix un impuls creixent per part de moltes empreses i universitats que estan invertint els seus recursos en aplicacions innovadores d'observació terrestre i comunicacions. Aquesta treball de fi de grau forma part d'un projecte de l'UPC NanoSat Lab per l'IEEE Geoscience and Remote Sensing Society titulat "Open PocketQube Kit". Aquest projecte té com a objectiu desenvolupar diferents PocketQubes educatius, un tipus de picosatèl·lits, amb forma de cub de 5 cm de mida, que aniran integrats dins de la missió del 3Cat-8. Precisament, aquest treball de fi de grau està centrat en el disseny i implementació del subsistema d'al·limentació elèctrica d'aquestes plataformes així com un anàlisi tèrmic pel conjunt de tota la missió.

© 2022 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, Transition metal oxide (TMOs) layers have interesting properties as selective contacts, i.e., hole or electron transport layers for novel semiconductor devices. Especially, oxides of molybdenum (MoO3), vanadium (V2O5), and tungsten (WO3) show good bahaviour acting as front hole-selective contacts for n-type crystalline-silicon heterojunction solar cells. Laser scribing has been widely used for thin-film ablation and seems the appropriate technology for device manufacturing with such non-conventional materials. In this work, we study the laser scribing of non-stoichiometric evaporated WOx, VOx, and MoOx films with three different wavelengths (1064, 532, and 355 nm) with pulse duration in the nanosecond and picosecond regimes. The selection of the proper laser source allows a wide parametric window, with complete removal of the TMO films and no alteration of the silicon substrate. The results on the isolation of diodes and their electrical characteristics show the quality of the laser scribing processes., Partial financial support has been provided by the Spanish Ministry of Science and Innovation under the projects CHENOC (ENE2016–78933-C4–1-R and ENE2016– 78933-C4–4-R) and SCALED (PID2019–109215RB-C41 and PID2019–109215RB-C44)., Peer Reviewed, Postprint (published version)

All-inorganic CsPbX3 (X = Cl, Br, I, or mixed halides) perovskite quantum dots (QDs) exhibit tunable optical bandgaps and narrow emission peaks, which have received worldwide interest in the field of both photovoltaics (PVs) and light-emitting diodes (LEDs). Herein, it is reported a discovery that CsPbI3 perovskite QD solar cell can simultaneously deliver high PV performance and intense electroluminescence. In specific, the multifunctional CsPbI3 QD film is fabricated through a simple yet efficient solid-state-ligand exchange process using a tailored organic ligand triphenyl phosphite (TPPI). The function of QD surface manipulation using TPPI here is proven to be twofold, balancing the carrier transport and effectively passivating the QD surface to produce conductive and emissive QD film. The CsPbI3 perovskite QD solar cell delivers a champion efficiency of 15.21% with improved open circuit voltage and high fill factor. Concurrently functioning as a red LED, the CsPbI3 perovskite QD solar cell outputs electric power to light conversion efficiency approaching 4%, a record value for QD electroluminescent PVs. The results here indicate that these versatile perovskite QDs may be a promising candidate for fabricating multifunctional optoelectronic devices., Peer Reviewed, Postprint (author's final draft)

Structural defects are ubiquitous for polycrystalline perovskite films, compromising device performance and stability. Herein, a universal method is developed to overcome this issue by incorporating halide perovskite quantum dots (QDs) into perovskite polycrystalline films. CsPbBr3 QDs are deposited on four types of halide perovskite films (CsPbBr3, CsPbIBr2, CsPbBrI2, and MAPbI3) and the interactions are triggered by annealing. The ions in the CsPbBr3 QDs are released into the thin films to passivate defects, and concurrently the hydrophobic ligands of QDs self-assemble on the film surfaces and grain boundaries to reduce the defect density and enhance the film stability. For all QD-treated films, PL emission intensity and carrier lifetime are significantly improved, and surface morphology and composition uniformity are also optimized. Furthermore, after the QD treatment, light-induced phase segregation and degradation in mixed-halide perovskite films are suppressed, and the efficiency of mixed-halide CsPbIBr2 solar cells is remarkably improved to over 11% from 8.7%. Overall, this work provides a general approach to achieving high-quality halide perovskite films with suppressed phase segregation, reduced defects, and enhanced stability for optoelectronic applications., Peer Reviewed, Postprint (author's final draft)

This work studies the use of polymeric layers of polyethylenimine (PEI) as an interface modification of electron-selective contacts. A clearly enhanced electrical transport with lower contact resistance and significant surface passivation (about 3 ms) can be achieved with PEI modification. As for other conjugated polyelectrolytes, protonated groups of the polymer with their respective counter anions from the solvent create an intense dipole. In this work, part of the amine groups in PEI are protonated by ethanol that behaves as a weak Brønsted acid during the process. A comprehensive characterization including high-resolution compositional analysis confirms the formation of a dipolar interlayer. The PEI modification is able to eliminate completely Fermi-level pinning at metal/semiconductor junctions and shifts the work function of the metallic electrode by more than 1 eV. Induced charge transport between the metal and the semiconductor allows the formation of an electron accumulation region. Consequently, electron-selective contacts are clearly improved with a significant reduction of the specific contact resistance (less than 100 mO·cm2). Proof-of-concept dopant-free solar cells on silicon were fabricated to demonstrate the beneficial effect of PEI dipolar interlayers. Full dopant-free solar cells with conversion efficiencies of about 14% could be fabricated on flat wafers. The PEI modification also improved the performance of classical high-efficiency heterojunction solar cells., This research has been supported by the Spanish government through Grants PID2019-109215RB-C41, PID2019109215RB-C43, PID2020-115719RB-C21, and PID2020116719RB-C41 and funded by MCIN/AEI/10.13039/ 501100011033. Besides this the authors would like to thank Prof. Jordi LLorca for his expertise and helpful discussions of XPS results, as well as Dr. Rodrigo Fernández-Pacheco of the Laboratorio de Microscopias Avanzadas (LMA-INA) of Zaragoza for the HRTEM images and EDS and EELS analysis, and Guillaume Sauthier from ICN2 for his contribution through UPS measurements and discussions., Peer Reviewed, Postprint (published version)

Earth-abundant semiconductors are a potential solution for the large-scale deployment of solar cells at a lower cost. Zinc phosphide (Zn3P2) is one type of earth-abundant semiconducting material, which has suitable optoelectronic properties for solar devices. Herein, we check the photovoltaic response of Zn3P2 thin films (<1um thick) grown on 325um thick InP substrates in different configurations. We studied the effect of thickness of the selective contact. An efficiency of 2.4% using polycrystalline Zn3P2 was obtained with the optimal selective contact stack configuration. Additionally, we observed that the combination of ITO and silver grid on top of Zn3P2 polycrystalline thin film gave an efficiency of 4.4%. The selectivity of the contacts is discussed using monocrystalline samples in differently doped InP substrates. The type of InP substrate and stoichiometry of Zn3P2 play a significant role in the contact selectivity and in the performance of the device. Our study gives an insight into the optimal device architecture for Zn3P2-based solar cells., Los semiconductores hechos de materiales abundantes a la Tierra pueden ser una solución por la implementación a gran escala de celdas solares poco costosas. El Zinc phosphide (Zn3P2) es un tipo de semiconductor hecho de materiales abundantes, que tiene propiedades optoelectrónicas óptimas para utilizarse en dispositivos solares. En este trabajo comprobamos la respuesta fotovoltaica de capas delgadas de Zn3P2 (grosor <1um) crecidas sobre sustratos de 325um de grosor de InP. Hemos estudiado el efecto del grosor de uno de los contactos selectivos utilizados, obteniendo una eficiencia de 2.4% en el caso óptimo con Zn3P2 policristalino . Adicionalmente, hemos observado que la combinación de ITO y Ag como contacto encima la capa delgada de Zn3P2 policristalino daba una eficiencia de 4,4%. La selectividad de los contactos se discute utilizando muestras monocristalinas crecidas sobre InP con diferente dopaje. El tipo de dopaje y la estequiometría del Zn3P2 tienen un rol significativo en el tipo de selectividad y en el rendimiento del dispositivo. El estudio da conocimiento respeto la arquitectura óptima para celdas solares basadas en Zn3P2., Els semiconductors fets de materials abundants a la Terra poden ser una solució per la implementació a gran escala de cel·les solars poc costoses. El Zinc phosphide (Zn3P2) és un tipus de semiconductor fet de materials abundants, que té propietats optoelectròniques òptimes per utilitzar-se en dispositius solars. En aquest treball comprovem la resposta fotovoltaica de capes primes de Zn3P2 (gruix <1um) crescudes sobre substrats de 325um de gruix d'InP. Hem estudiat l'efecte del gruix d'un dels contactes selectius utilitzats, obtenint una eficiència de 2.4% en el cas òptim amb Zn3P2 policristal·lí . Addicionalment, hem observat que la combinació d'ITO i Ag com a contacte damunt la capa prima de Zn3P2 policristal·lí donava una eficiència de 4,4%. La selectivitat dels contactes es discuteix utilitzant mostres monocristal·lines crescudes sobre InP amb diferent dopatge. El tipus de dopatge i la estequiometria del Zn3P2 tenen un rol significant en el tipus de selectivitat i en el rendiment del dispositiu. L'estudi dona coneixement respecte l'arquitectura òptima per a cel·les solars basades en Zn3P2.

The phenomena related to charge trapping are among the most relevant open issues that affect the long-term stability of perovskite-based devices. According to this, the objective of this paper is to report experimental results in which a charge control strategy is used for the first time in a solar cell structure that has a high trap density perovskite absorber. This device has also noticeable J-V hysteresis, produced by non-capacitive effects. The control strategy proposed, based on sigma-delta modulation, applies to the device an appropriate sequence of voltage waveforms determined after periodical current measurements made at a constant voltage. The experimental results obtained and the fittings made with a phenomenological model indicate that this approach allows controlling several charge-related effects. As a consequence, the J-V characteristic of the device is successfully shifted and stabilized to predetermined positions., This research was funded by the Spanish Ministry MINECO (under grant RTI2018-098728- B-C33), the Severo Ochoa program (under grant SEV-2015-0522), MINECO and FEDER (under grant MAT2017-89522-R), the Fundacio Privada Cellex and the CERCA program from the Generalitat de Catalunya., Peer Reviewed, Postprint (published version)

Solar cells based on quaternary kesterite compounds like Cu2ZnGeSe4 are complex systems where the variation of one parameter can result in changes in the whole system, and, as consequence, in the global performance of the devices. In this way, analyses that take into account this complexity are necessary in order to overcome the existing limitations of this promising Earth-abundant photovoltaic technology. This study presents a combinatorial approach for the analysis of Cu2ZnGeSe4 based solar cells. A compositional graded sample containing almost 200 solar cells with different [Zn]/[Ge] compositions is analyzed by means of X-ray fluorescence and Raman spectroscopy, and the results are correlated with the optoelectronic parameters of the different cells. The analysis results in a deep understanding of the stoichiometric limits and point defects formation in the Cu2ZnGeSe4 compound, and shows the influence of these parameters on the performance of the devices. Then, intertwined connections between the compositional, vibrational and optoelectronic properties of the cells are revealed using a complex analytical approach. This is further extended using a machine learning algorithm. The latter confirms the correlation between the properties of the Cu2ZnGeSe4 compound and the optoelectronic parameters, and also allows proposing a methodology for device performance prediction that is compatible with both research and industrial process monitoring environments. As such, this work not only provides valuable insights for understanding and further developing the Cu2ZnGeSe4 photovoltaic technology, but also gives a practical example of the potential of combinatorial analysis and machine learning for the study of complex systems in materials research., Peer Reviewed, Postprint (published version)

Tandem solar cells are an innovative technology that allows us to join two or more solar cells with different light spectrum absorption properties and thus be able to increase the efficiency of the total system. Joining the cells is not an easy task, as the binding nexus must be as efficient as possible. In this project, we designed the intermediate layer using ITO (and Ag when we needed for making measurements) on an ETL (Electron Transport Layer) formed mainly by a phosphorus diffusion region on crystalline silicon substrates. Later, we studied two of the parameters that could most affect our efficiency. After the experiments carried out, we observed that our results are good at relatively low temperatures (0 - 200 ° C), allowing us to manufacture tandem structures under these conditions., Las celdas solares tándem son una innovadora tecnología que nos permite unir dos o más celdas solares con diferentes propiedades de absorción del espectro de luz y así poder aumentar la eficiencia del sistema total. Unir las celdas es una tarea no del todo fácil, ya que la capa intermedia entre celdas debe permitir conservar la mayor eficiencia posible. En este proyecto hemos diseñado la capa intermedia usando ITO (y Ag cuando lo hemos necesitado para hacer medidas) sobre una ETL (Electron Transport Layer) formada principalmente por una difusión de fósforo. Posteriormente, hemos estudiado dos de los parámetros que más nos podían afectar a la eficiencia. Tras los experimentos realizados observamos que nuestros resultados son buenos a temperaturas relativamente bajas (0 - 200 °C), permitiéndonos fabricar estructuras tándem en esas condiciones., Les cel·les solars tàndem son una innovadora tecnologia que ens permet unir dues o més cel·les solars amb diferents propietats d'absorció de l'espectre de llum i així poder augmentar l'eficiència del sistema total. Unir les cel·les és una tasca no del tot fàcil, ja que el nexe d'unió ha de permetre conservar la major eficiència possible. En aquest projecte hem dissenyat la capa intermèdia usant ITO (i Ag quan l'hem necessitat per a fer mesures) sobre una ETL (Electron Transport Layer) formada principalment per una difusió de fòsfor i, posteriorment, hem estudiat dos dels paràmetres que més ens podien afectar a l'eficiència. Després dels experiments, hem observat que els nostres resultats son bons a temperatures relativament baixes (0 - 200 ° C), cosa que ens permet fabricar estructures en tàndem en aquestes condicions.

The fabrication of soda lime glass/fluorine-doped tin oxide (SLG/FTO) transparent substrates represents an important advance in the fabrication of tandem solar cells. In addition, possible passivation using Al2O3, which can be deposited using cheap systems, can open up the development of Cu2ZnSnS4 (CZTS) solar cells. In this work, we report the simultaneous use of FTO/Mo (20 nm) as a transparent substrate and Al2O3 as apassivation layer at the p–n interface in CZTS solar cells. The best devices show efficiencies of 7.7% (Voc = 677 mV) and 7.3% (Voc = 700 mV). Complete analysis, in terms of morphology, structure and electrical properties, is discussed., Peer Reviewed, Postprint (author's final draft)

Germanium-based wide band gap kesterite semiconductor Cu2ZnGe(S,Se)4 (CZGeSSe) is considered a very promising absorber compound as top cell in tandem devices. Autonomy to tailor the band gap from ~1.47 eV (Cu2ZnGeSe4-CZGeSe) to ~2.2 eV (Cu2ZnGeS4-CZGeS), as well as non-toxic constituents makes this compound a strong candidate for further scientific exploration. However, the record efficiency of Cu2ZnGeSe4 solar cells is still significantly lower than those of its predecessors Cu2ZnSn(SxSe1-x)4 (CZTSSe), Cu(In,Ga)Se2 (CIGS) and CdTe thin-film solar cells. The comprehensive understanding of the factors limiting the performance of Cu2ZnGeSe4 based solar cells is the purpose of this work, by combining a complete characterization of the morphological, structural, compositional and optoelectronic properties of Cu2ZnGeSe4 absorbers and devices. Besides, an in-depth investigation of the main limitations is carried out, specifically focusing on studying the origin of the large VOC deficit, the main recombination mechanisms, electric transport properties, band tails and possible Cu2ZnGeSe4/CdS band offset effects. The champion CZGeSe solar cell device reported in this work shows an efficiency of 6.5%, Voc of 606 mV, JSC of 17.8 mA/cm2 and FF of 60%. The results presented here demonstrate that the large voltage deficit of CZGeSe solar cells could be mainly ascribed to a Fermi level pinning at the interface, while modifications of the buffer layer to induce a “spike” at the p-n junction could be beneficial. Additionally, low carrier diffusion lengths and lifetimes, along with possible back contact recombination, are identified as the main culprits for the limited carrier collection for low-energy photons. Finally, some strategies are proposed to face and overcome most of these issues and to help improving the CZGeSe performance., Peer Reviewed, Postprint (author's final draft)

Semi-transparent solar cells are the next step for photovoltaics into our daily life. Over the last years, kesterite-type material has attracted a special attention to be used as an absorber in thin-film solar cells because of its low toxicity and earth abundant constituents. Here, Cu2ZnGeSe4 (CZGSe) thin films are grown by co-evaporation and subsequent annealing at a maximum temperature of 480 °C or 525 °C onto Mo/V2O5/FTO/glass stacks. The goal of this work is to investigate the influence of the annealing temperature on the composition, morphology, vibrational properties, and transmittance of CZGSe layers, the formation of secondary phases, and distribution of elements within the absorber layer as well as on the optoelectronic properties of the corresponding solar cell devices. Raising the annealing temperature to 525 °C leads to a more uniform distribution of Cu, Zn, Ge and Se throughout the absorber layer, a reduction of the presence of the GeSe2 secondary phase, which is mainly detected at 480 °C, a larger grain size and the formation of a thicker MoSe2 layer at the CZGSe/back contact interface. The strategy of increasing the annealing temperature allows for improved J–V characteristics and higher spectral response resulting in an enhanced device performance of 5.3% compared to 4.2% when using 525 °C and 480 °C, respectively. Both absorber layers present an optical band gap energy of 1.47 eV. Furthermore, higher annealing temperature has beneficial effect to the CZGSe-based devices without losses in total transmitted light because of the higher diffuse transmittance. This work shows first promising semi-transparent CZGSe-based solar cells possibly open up new routes of applications., Peer Reviewed, Postprint (published version)

The potential of tandem solar cells combining two chalcopyrite absorbers is evaluated using numerical modeling based on an exhaustive set of experimental parameters, offering a high degree of confidence in the numerical values reported herein. The simple yet reliable approach used here combines a transfer matrix-based optical model of the wide bandgap CIGSe top subcell used as input for the 1D electrical modeling of a reference narrow bandgap CIGSe bottom cell. Various optical optimizations to the top subcell are investigated, with the aim to increase the bottom subcell current and reduce the efficiency threshold needed at the top subcell for the tandem device to beat the current single junction efficiency record. The results here suggest that significant progress compared with the state of the art can be made using a pure CuGaSe2 absorber combined with an optimized back contact with an ultrathin transition metal oxide interlayer. With a bottom subcell current more than doubled in the optimum top subcell configuration, a challenging yet clear pathway for the future realization of tandem solar cells based on chalcopyrite absorbers is offered., Peer Reviewed, Postprint (published version)

© 2021 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, This work explores the use of very thin transparent vanadium oxide films deposited by atomic layer deposition (ALD) technique as hole transport layer for CZTSe solar cells as alternative of opaque molybdenum based contacts. Contact resistivity between the CZTSe absorber and the ALD V2Ox contact was measured. In order to improve contact quality, a cleaning bath using hydrofluoric acid (HF) dip, was also analyzed and its influence on kesterite surface was studied. Elementary material characterization and composition analysis of the V2Ox layers was performed. Contact quality was assessed yielding contact resistivity values below 9 and 30 mOcm2 for ALD and thermal evaporated V2Ox films respectively. The proposed ALD V2Ox based hole transport layer was deposited onto a glass covered with a transparent conductive oxide forming part of the rear contact scheme of a vertical CZTSe solar cell with a conventional ITO/CdS stack as electron transport layer. The impact of subsequent thermal post-annealing treatments in the cell performance was also analyzed yielding efficiency up to 3.9% on a semi-transparent CZTSe solar cell without any additional optimization process. In this way, a CZTSe solar cell with both transparent electrodes has been demonstrated paving the way to obtain in the future high efficiency bifacial and/or semitransparent Building –integrated photovoltaic devices., Authors acknowledge the use of instrumentation as well as the technical advice provided by the National Facility ELECMI ICTS, node "Laboratorio de Microscopias Avanzadas" at Universidad de Zaragoza; moreover, this work has been supported by the Ecuadorian government grants SENESCYT (BECAS DE POSGRADOS INTERNACIONALES 2018), Spanish Government through projects IGNITE (ENE2017-87671-C3-2-R) - SCALED (PID2019-109215RB-C41) and the European Research Council Grant Horizon 2020 CUSTOM-ART project (Grant agreement ID: 952982) and Ministerio de Ciencia e Innovación, grant number PID2020-116719RB-C41, Peer Reviewed, Postprint (author's final draft)

A method to probe the depth morphology, defect profile and possible secondary phases in a thin film semiconductor is presented, taking a standard Kesterite film as an example. Using a top-down approach based on a previously reported controlled Methanol-Br2 chemical etching, well-defined slabs of a state of the art Kesterite absorber are fabricated. The analysis of their morphology both by Scanning Electron Microscopy and 3D optical Profilometry reveals the extent of a previously reported poor film morphology toward the back interface, and we are able to determine that more than 50% of a standard absorber is disconnected from the substrate. More importantly, these etched films are subsequently analyzed by surface sensitive techniques such as X-ray Photoelectron Spectroscopy and UV-Raman analysis. An accurate composition profile is established, and for the first time, a direct observation of the defects’ nature and their depth profiling in Kesterite is made possible. While VCu are found with a constant amount throughout the absorber, indicating a homogenous carrier concentration, a prevalence of the ZnSn defect is observed with a steep gradient toward the back interface, associated with an increase in the SnSe2 secondary phase. With bulk defects being often pointed out as the intrinsic limitation of this material, this result highlights what possibly is the main impediment of Kesterite solar cells, and a critical point to address in the design of future devices. Beyond the case of Kesterite absorbers, the method presented here offers a combination of simplicity, tunability and versatility making a straightforward transfer to other emerging thin film absorbers feasible, and it could possibly be an important tool in their future performance assessment and comparison., Peer Reviewed, Postprint (author's final draft)

Photovoltaic energies are essential for a transition from the current energy model towards one more sustainable and efficient. Today, pn junction technology dominates the world market, breaking records of efficiency and of production cost. Even so, there are some problems associated with this technology that together with the desire of knowledge of the scientific community have led to the study of new solar cells structures, selective contacts. This technology changes the vision of why the carriers move within the device, they do not move by the electric field generated by the union, but by the gradient of electrochemical potential between the different materials that form it. For its correct operation, materials with very specific work functions are needed, which limits the possible materials to use, moreover most of they are scarce on the planet. Due to these limitations, the idea of using dipole layers to modify the work function of the contacts arises and, in this way, the possibility of using more common materials grows, both in abundance and in the use of deposit techniques. In this context we have worked with the organic molecule Histidine for the manufacture of selective contacts together with other passivating layers that had previously demonstrated their efficiency. One of the manufactured samples has good characteristics for operation as selective contact, although it is not good enough for the use in a solar cell. Even so, this gives us an idea of where research should be oriented., Las energías fotovoltaicas son imprescindibles para una transición del modelo energético actual hacia una más sostenible y eficiente. En la actualidad la tecnología de las uniones pn domina el mercado mundial, rompiendo récords de eficiencia y también de coste de producción. Aun así, existen algunos problemas asociados a esta tecnología que unidos al afán de conocimiento de la comunidad científica han llevado al estudio de nuevas estructuras de células solares, los contactos selectivos. Esta tecnología cambia la visión de porque se mueven los portadores dentro del dispositivo, no se mueven por el campo eléctrico generado por la unión, sino por el gradiente de potencial electroquímico entre los diferentes materiales que la conforman. Para su correcto funcionamiento se necesitan materiales con funciones de trabajo muy específicas lo que limita los posibles materiales para utilizar, además la mayoría de estos son escasos en el planeta. Debido a estas limitaciones surge la idea de utilizar capas dipolares para modificar la función de trabajo de los contactos que se utilizan y de esta forma poder utilizar materiales más comunes, tanto en abundancia como en el uso de técnicas de depósito. En este contexto se ha trabajado con la molécula orgánica Histidine para la fabricación de contactos selectivos juntamente con otras capas pasivadoras que habían demostrado su eficiencia anteriormente. Una de las muestras fabricadas presenta buenas características para el funcionamiento como contacto selectivo, aunque no es suficientemente bueno para utilizarlo en una célula solar. Aun así, esto nos da una idea de hacia dónde deben seguir las investigaciones., Les energies fotovoltaiques són imprescindibles per una transició del model energètic actual cap a un de més sostenible i eficient. A l?actualitat la tecnologia de les unions pn domina el mercat mundial, trencat rècords d?eficiència i també de costos de producció. Encara així, existeixen alguns problemes associats a aquesta tecnologia que units amb l?afany de coneixement de la comunitat científica han portat a l?estudi de noves estructures de cèl·lules solar, els contactes selectius. Aquesta tecnologia canvia la visió de perquè es mouen els portadors dins del dispositiu, no es mouen pel camp elèctric generat a la unió, sinó pel gradient de potencial electroquímic entre els diferents materials que la conformen. Pel correcte funcionament es necessiten materials amb funcions de treball molt específiques el que limita els possibles materials per utilitzar, a més a més la majoria d?aquests són escassos al planeta. Degut a aquestes limitacions sorgeix la idea d?utilitzar capes dipolars per modificar la funció de treball dels contactes que s?utilitzen i d?aquesta forma poder utilitzar materials més comuns, ja sigui en abundància com en l?ús de les tècniques de dipòsit. En aquest context s?ha treballat amb la molècula orgànica Histidine per la fabricació de contactes selectius juntament amb altres capes pasivadores que havien demostrat la seva eficiència amb anterioritat. Una de les mostres fabricades presenta bones característiques pel funcionament com a contacte selectiu, encara que no es suficientment bo per utilitzar-lo en una cèl·lula solar. De tota manera, això ens dona una idea de cap a on han de dirigir-se la recerca en aquest àmbit.

Wide bandgap organic-inorganic hybrid perovskites (OIHPs) have shown great potential to improve the efficiency of tandem solar cells. Furthermore, a perovskite absorption layer with excellent surface morphology, i.e. smooth surface, and large grain size is crucial for fabricating efficient perovskite solar cells (PSCs). In this work, both compositional and solvent engineering are performed to improve the quality of the perovskite absorption layer and reach a better photovoltaic performance. This study includes a characterization of both the material and the devices themselves (absorbance and photoluminescence spectroscopy and J-V curves). In order to improve the optical and morphological properties of the wide bandgap perovskites, the behaviour of different antisolvents are studied: common antisolvents (e.g. Chlorobenzene), green antisolvents (e.g. Methyl Benzoate) and mixtures of antisolvents. As a result, Methyl Benzoate (MB) and a mixture of MB with Hexane are promising antisolvents for engineering high-quality perovskites layers., Outgoing

This work aims to unveil the optimal annealing conditions and surface treatments of CZGeSe absorbers, synthesized using vacuum-based deposition technique, with an eye to optimizing the main parameters allowing better control of secondary phases formation and improving crystalline quality of this absorber. Firstly, a comparative study is given of one and two-step annealing profiles, where, for each thermal treatment, the optimal temperature is probed. The second section of this study underlines the evaluation of the surface treatment effect on the as-annealed absorber using different etching agents. Finally, the effect of different post-annealing treatment temperatures on the overall performance of the fabricated devices is evaluated. For the studied optimizations, a deep understanding of the cell behavior is provided through structural, morphological and electrical characterizations. Preliminary results have given an efficiency up to 5.6% with higher Voc = 572 mV and FF = 65% compared to the reported record cell using similar absorber (Voc = 558 mV, FF = 59%). This performance is linked to the implementation of a two-step annealing process with lower temperatures (330 °C/480 °C) as it showed the best crystallinity-efficiency trade-off along with the smallest amount of ZnSe secondary phase among all the thermal routines studied. In addition, after the evaluation of several etching agents, the implementation of a KCN etching has shown to be the most effective leading to a remarkable improvement of the PN junction through a surface passivation., Peer Reviewed, Postprint (author's final draft)

© <2020>. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0, Localized p-doped nanojunctions (200–300 nm in diameter) were formed in n-type crystalline silicon substrates and were characterized using scanning electron microscopy (SEM) and conductive-probe atomic force microscopy (C-AFM). Localized doping was performed by diffusion through sub-micron sized holes in a silicon-oxide mask defined using self-organized polystyrene nanoparticles. After oxide removal, a significant brightness contrast in the SEM top and side view images strongly suggested the successful local doping of these areas. Furthermore, local current-voltage measurements performed by C-AFM revealed an open circuit voltage and a short-circuit current only in the areas defined as nanojunctions. This photovoltaic effect is driven by the laser used to control cantilever deflection in the AFM., We acknowledge the financial support of the InnoEnergy PhD School Program and the European Institute of Technology (EIT). This work was partially funded by the Spanish government under projects TEC2017-82305-R, ENE2016-78933-C4-1-R and ENE2017-87671-C3-2-R, and by the Agence Nationale de la Recherche through the ANR project “APOCALYPSO” (ANR-13- PRGE-0003-01)., Peer Reviewed, Postprint (author's final draft)

This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in Transition-Metal Oxides for Kesterite Solar Cells Developed on Transparent Substrates, copyright © American Chemical Society after peer review. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acsami.0c06992, Fabrication on transparent soda-lime glass/fluorine-doped tin oxide (FTO) substrates opens the way to advanced applications for kesterite solar cells such as semitransparent, bifacial, and tandem devices, which are key to the future of the PV market. However, the complex behavior of the p-kesterite/n-FTO back-interface potentially limits the power conversion efficiency of such devices. Overcoming this issue requires careful interface engineering. This work empirically explores the use of transition-metal oxides (TMOs) and Mo-based nanolayers to improve the back-interface of Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 solar cells fabricated on transparent glass/FTO substrates. Although the use of TMOs alone is found to be highly detrimental to the devices inducing complex current-blocking behaviors, the use of Mo:Na nanolayers and their combination with n-type TMOs TiO2 and V2O5 are shown to be a very promising strategy to improve the limited performance of kesterite devices fabricated on transparent substrates. The optoelectronic, morphological, structural, and in-depth compositional characterization performed on the devices suggests that the improvements observed are related to a combination of shunt insulation and recombination reduction. This way, record efficiencies of 6.1, 6.2, and 7.9% are obtained for Cu2ZnSnSe4, Cu2ZnSnS4, and Cu2ZnSn(S,Se)4 devices, respectively, giving proof of the potential of TMOs for the development of kesterite solar cells on transparent substrates., This research was supported by the H2020 Programme under the project INFINITE-CELL (H2020-MSCA-RISE-2017-777968), by the Ministry of Science and Innovation of Spain under IGNITE project (ENE2017-87671-C3-1-R), by the European Regional Development Funds (ERDF, FEDER Programa Competitivitat de Catalunya 2007–2013) and CERCA Programme / Generalitat de Catalunya. Authors from IREC belong to the SEMS (Solar Energy Materials and Systems) Consolidated Research Group of the “Generalitat de Catalunya” (Ref. 2017 SGR 862), Peer Reviewed, Postprint (author's final draft)

Nowadays, one of the most urgent and important problems that humankind has to face is climate change and global warming. One way to approach it, is by changing the way energy is produced from non-renewable sources, such as coal or gas, to renewable sources, like wind or solar power. In this report, the focus is set on solar energy and how to improve the efficiency of photovoltaic solar cells. Titanium nitride (TiNx) is studied as an electron selective contact to possibly substitute magnesium-aluminium (Mg/Al). Several experiments were carried out changing the sputtering deposition conditions such as the concentration of N2 gas used during the deposition or the deposition time. However, the results obtained were not satisfactory enough. A new material, ITO (Indium Tin Oxide) on an electron doped substrate (n+), was also tested and positive results were yielded. A contact resistivity of approximately ?c = 80 m?cm2 was achieved., Hoy en día, uno de los problemas más urgentes e importantes que la humanidad tiene que enfrentar es el cambio climático y el calentamiento global. Una forma de abordarlo es cambiando la forma en que se produce energía de fuentes no renovables, como el carbón o el gas, a fuentes renovables, como la energía eólica o solar. En este informe, la atención se centra en la energía solar y en cómo mejorar la eficiencia de las células solares fotovoltaicas. El nitruro de titanio (TiNx) se estudia como contacto selectivo de electrones para posiblemente sustituir el magnesio-aluminio (Mg/Al). Se llevaron a cabo varios experimentos cambiando las condiciones de deposición por sputtering, como la concentración de N2 gas utilizada durante la deposición o el tiempo de deposición. Sin embargo, los resultados obtenidos no fueron lo suficientemente satisfactorios. También se probó un nuevo material, ITO (Indium Tin Oxide) en un sustrato dopado de electrones (n+), y se obtuvieron resultados positivos. Se logró una resistividad de contacto de aproximadamente ?c = 80 m?cm2., Avui en dia, un dels problemes més urgents i importants que ha d?afrontar la humanitat és el canvi climàtic i l?escalfament global. Una manera d?abordar-lo és canviar la manera com es produeix l?energia de fonts no renovables, com el carbó o el gas, a fonts renovables, com l?energia eòlica o solar. En aquest informe, l'atenció es centra en l?energia solar i en com millorar l?eficiència de les cèl·lules solars fotovoltaiques. El nitrur de titani (TiNx) s?estudia com a contacte selectiu d?electrons per possiblement substituir el magnesi-alumini (Mg/Al). Es van realitzar diversos experiments canviant les condicions de diposició per sputtering, com ara la concentració de N2 gas utilitzada durant el dipòsit o el temps de diposició. Tot i això, els resultats obtinguts no van ser prou satisfactoris. També es va provar un nou material, ITO (Indium Tin Oxide) en un substrat dopat d'electrons (n ??+), i es van obtenir resultats positius. Es va aconseguir una resistivitat de contacte d?aproximadament ?c = 80 m?cm2.

The content of this final degree project tries to explain the company in which I have done the practices for the last 6 months and the work that I have been doing. During this period in the company Erca Europe SL, the head of the company itself has been my tutor, who has guided, taught and advised me during this experience. The main functions that I have carried out specifically within this company has been to manage some of the projects that have entered, from the first contact with the client until its completion, making designs, budgets, site visits or quality controls. Other work I have done has been the supervision of project documentation, real estate valuations, meetings with industrialists and contractors, damage reports on buildings and homes and very active collaboration with the rest of the office team, where I have learned a great deal amount of things from and with them.