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The preparation process for CZTSe absorbers at UOL includes an independent tuning of the starting and ending composition of the layer in terms of Cu/Sn ratio. This is realized by a composition shift during the high temperature step of the annealing/selenization by Sn incorporation / Sn loss from the layer. In this work, we present a correlation between the precursor/absorber composition and the resulting device parameters. In brief, different starting compositions have a fundamental influence on the alloy structure of the precursor and hence can influence the dominating reaction pathway. For the Cu rich case the dominating alloy is Cu3Sn which moves towards Cu6Sn5 + Cu3Sn for lower Cu/Sn ratios. For high added Sn amounts the fraction of non-alloyed elemental Sn in the precursor layer rises. These differences can influence the reaction pathway and the resulting defect landscape, leading to a significant influence on final device properties. A series of precursors with different Cu/Sn ratios were processed in identical annealing conditions ending up with an absorber composition in the usual composition region, favourable for high efficiency devices. The resulting device properties such as PCE, EU, VOC-def and long-term device stability (after 1000h accelerated aging at 85°C) were found to correlate with the starting composition. Preliminary results from low-temperature PL analysis indicate an influence on activation energies of defects.

Here we investigated a novel layer-based optimization technique to improve the performance of a CZTSe solar cell. By using this technique, the optical behavior and electrical properties of the proposed solar cell improved significantly as a result of the changes in the layer specifications and the layer materials. The structure of the cell consisted of an absorber laid on a conducting layer and covered by Indium Tin Oxide (ITO), with ZnO on its top surface. Due to the employment of the CSLO technique, a p+pn junction was formed between the absorber and window layers, which provided a lower recombination rate by transmitting more electrons and holes to the contacts. In addition, the main important parameters affecting the solar cell’s performance such as layer thickness, carrier lifetime, and total effect density were investigated. According to the results, the proposed CZTSe solar cell achieved a 32.6% and 79.5% efficiency and fill factor, respectively—which in comparison to a conventional solar cell is remarkable. Moreover, hybrid structures made by utilizing CZTS-based, Ge-based Cu2ZnGeSe4, and Si-based Cu2ZnSiSe4 with the proposed CZTSe-based solar cell were implemented and better results were achieved, yielding an efficiency of about 42, 50, and 34% and a fill factor of 66, 55, and 42%, respectively, due to the materials’ properties.

© 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

In this work, the computational analysis on use of nanostructures to both III-Nitride and Kesterite solar cell are presented and compared. The scope behind the comparative analysis of III-nitride and kesterite material based solar cells is due to their excellent material properties, which made them suitable as an absorber for solar cells. In III-nitride based solar cells, stress induced polarization charges play an important role in carrier dynamics of cell, whereas, kesterite based cells suffer from detrimental effect due to its in-house defects. Here, an analysis is carried out to understand the above mentioned important effects, i.e., carrier transport mechanisms under the influence of polarization charges in III-nitride materials and in presence of defects in kesterite materials with nanostructures. It is anticipated that, nanostructures provide lots of advantages over bulk layer in order to overcome the detrimental effects in solar cells. A detailed comparative analysis of both type of solar cells are carried out. Finally, quantum efficiency measurement is carried out in order to observe the range of light absorption in each structures. It is quite interesting to observe that nanostructure doesn't boost the performance of the solar cell unless until the device is engineered properly. It is purely depends on carrier recovery and transport from the nanostructures.

New solar cells with Ag/C60/MAPbI3/Cu2ZnSnSe4 (CZTSe)/Mo/FTO multilayered structures on glass substrates have been prepared and investigated in this study. The electron-transport layer, active photovoltaic layer, and hole-transport layer were made of C60, CH3NH3PbI3 (MAPbI3) perovskite, and CZTSe, respectively. The CZTSe hole-transport layers were deposited by magnetic sputtering, with the various thermal annealing temperatures at 300 °C, 400 °C, and 500 °C, and the film thickness was also varied at 50~300 nm The active photovoltaic MAPbI3 films were prepared using a two-step spin-coating method on the CZTSe hole-transport layers. It has been revealed that the crystalline structure and domain size of the MAPbI3 perovskite films could be substantially improved. Finally, n-type C60 was vacuum-evaporated to be the electronic&nbsp, transport layer. The 50 nm C60 thin film, in conjunction with 100 nm Ag electrode layer, provided adequate electron current transport in the multilayered structures. The solar cell current density–voltage characteristics were evaluated and compared with the thin-film microstructures. The photo-electronic power-conversion efficiency could be improved to 14.2% when the annealing temperature was 500 °C and the film thickness was 200 nm. The thin-film solar cell characteristics of open-circuit voltage, short-circuit current density, fill factor, series-resistance, and Pmax were found to be 1.07 V, 19.69 mA/cm2, 67.39%, 18.5 Ω and 1.42 mW, respectively.

Kesterite-structured Cu2ZnSnSe4 (CZTSe) is considered as one of the Earth-abundant and non-toxic photovoltaic materials. CZTSe films have been prepared using a single-step co-evaporation method at a relatively low temperature (i.e., below 500 °C). Due to the volatile nature of tin-selenide, the control over substrate temperature (i.e., growth temperature) is very important in terms of the deposition of high-quality CZTSe films. In this regard, the effects of growth temperatures on the CZTSe film morphology were investigated. The suitable temperature range to deposit CZTSe films with Cu-poor and Zn-rich compositions was 380−480 °C. As the temperature increased, the surface roughness of the CZTSe film decreased, which could improve p/n junction properties and associated device performances. Particularly, according to capacitance-voltage (C-V) and derived-level capacitance profiling (DLCP) measurements, the density of interfacial defects of CZTSe film grown at 480 °C showed the lowest value, of the order of ~3 × 1015 cm−3. Regardless of applied growth temperatures, the formation of a MoSe2 layer was rarely observed, since the growth temperature was not high enough to have a reaction between Mo back contact layers and CZTSe absorber layers. As a result, the photovoltaic (PV) device with CZTSe film grown at 480 °C yielded the best power conversion efficiency of 6.47%. It is evident that the control over film growth temperature is a critical factor for obtaining high-quality CZTSe film prepared by one-step process.

In recent years, the search for more efficient and environmentally friendly materials to be employed in the next generation of thin film solar cell devices has seen a shift towards hybrid halide perovskites and chalcogenide materials crystallising in the kesterite crystal structure. Prime examples for the latter are Cu2ZnSnS4, Cu2ZnSnSe4, and their solid solution Cu2ZnSn(SxSe1−x)4, where actual devices already demonstrated power conversion efficiencies of about 13 %. However, in their naturally occurring kesterite crystal structure, the so-called Cu-Zn disorder plays an important role and impacts the structural, electronic, and optical properties. To understand the influence of Cu-Zn disorder, we perform first-principles calculations based on density functional theory combined with special quasirandom structures to accurately model the cation disorder. Since the electronic band gaps and derived optical properties are severely underestimated by (semi)local exchange and correlation functionals, supplementary hybrid functional calculations have been performed. Concerning the latter, we additionally employ a recently devised technique to speed up structural relaxations for hybrid functional calculations. Our calculations show that the Cu-Zn disorder leads to a slight increase in the unit cell volume compared to the conventional kesterite structure showing full cation order, and that the band gap gets reduced by about 0.2 eV, which is in very good agreement with earlier experimental and theoretical findings. Our detailed results on structural, electronic, and optical properties will be discussed with respect to available experimental data, and will provide further insights into the atomistic origin of the disorder-induced band gap lowering in these promising kesterite type materials.

The Zn-rich and Cu-poor Cu2ZnSnSe4 (CZTSe) thin films were produced on flexible Mo foil by the three-step process. The XRD analysis demonstrates that the film mainly consists of CZTSe tetragonal phase and can contained ZnSe secondary phase. In addition, there are reflections of Mo and MoSe2. It was found that the crystal structure of the CZTSe films deposited on a Mo foil substrate was stable at low temperatures. The lattice parameters a and c are linearly decreasing in rang 5.707–5.637 and 11.394–11.298 A, respectively, with a change in the temperature of the X-ray measurements from the 300 to 100 K. The thermal expansion coefficient is 9.87 ? 10–6 K–1.

Dissertation work aimed to investigate the laser processing of the P2 and P3 scribes in thin-film solar cells searching for optimal laser pulse duration, laser repetition rate, wavelength, and various scribing approaches based on the in-house developed novel direct electrical measurement technique of electrical performance of the thin-film solar cells. The dissertation work consists of an introduction, author’s publication list, literature review, methods, results, conclusions, references and a summary. In the thesis, a novel direct electrical measurement technique (LLST) was developed and investigated in CIGS and CZTSe thin-film solar cells. LLST measurements revealed the relationship between the P3 scribe conductivity and the used laser wavelength. Increasing the laser pulse repetition rate, increased heat accumulation in the cells, which was observed as the pronounced melting of the laser-scribed areas and increased scribe conductivity. Finally, it was shown that scribing with picosecond duration pulses at the 1 MHz pulse repetition rate could locally transform a CIGS absorber layer into a highly conductive compound suitable to act as a P2 interconnect.

Dissertation work aimed to investigate the laser processing of the P2 and P3 scribes in thin-film solar cells searching for optimal laser pulse duration, laser repetition rate, wavelength, and various scribing approaches based on the in-house developed novel direct electrical measurement technique of electrical performance of the thin-film solar cells. The dissertation work consists of an introduction, author’s publication list, literature review, methods, results, conclusions, references and a summary. In the thesis, a novel direct electrical measurement technique (LLST) was developed and investigated in CIGS and CZTSe thin-film solar cells. LLST measurements revealed the relationship between the P3 scribe conductivity and the used laser wavelength. Increasing the laser pulse repetition rate, increased heat accumulation in the cells, which was observed as the pronounced melting of the laser-scribed areas and increased scribe conductivity. Finally, it was shown that scribing with picosecond duration pulses at the 1 MHz pulse repetition rate could locally transform a CIGS absorber layer into a highly conductive compound suitable to act as a P2 interconnect.

In this work, results are reported concerning the effect of the deposition parameters on the structural properties of Cu 2 ZnSnSe 4 (CZTSe) thin films, grown through a chemical reaction of the metallic precursors by co-evaporation in a two-stage process. XRD measurements revealed that the samples deposited by selenization of Cu and Sn grow in the kesterite phase (CZTSe), respectively. Effect of the deposition temperature and mass ratio Cu/ZnSe on the transport properties of CZTSe films were analyzed. It was also found that the electrical conductivity of the thin films is affected by the transport of free carriers in extended states of the conduction band as well as for variable range hopping transport mechanisms, each one predominating in a different temperature range. The molecular and morphological effect on the compound through Raman and AFM measurements was studied. © 2016 Elsevier B.V.

Contact layers play an important role in thin film solar cells, but new material development and optimization of its thickness is usually a long and tedious process. A high-throughput experimental approach has been used to accelerate the rate of research in photovoltaic (PV) light absorbers and transparent conductive electrodes, however the combinatorial research on contact layers is less common. Here, we report on the chemical bath deposition (CBD) of CdS thin films by combinatorial dip coating technique and apply these contact layers to Cu(In,Ga)Se-2 (CIGSe) and Cu2ZnSnSe4 (CZTSe) light absorbers in PV devices. Combinatorial thickness steps of CdS thin films were achieved by removal of the substrate from the chemical bath, at regular intervals of time, and in equal distance increments. The trends in the photoconversion efficiency and in the spectral response of the PV devices as a function of thickness of CdS contacts were explained with the help of optical and morphological characterization of the CdS thin films. The maximum PV efficiency achieved for the combinatorial dip-coating CBD was similar to that for the PV devices processed using conventional CBD. The results of this study lead to the conclusion that combinatorial dip-coating can be used to accelerate the optimization of PV device performance of CdS and other candidate contact layers for a wide range of emerging absorbers.

Polycrystalline powder samples of eight very far off‐stoichiometric Cu2ZnSnSe4(CZTSe) compounds (off‐stoichiometry types A–D) are grown using the solid‐state reaction method in evacuated silica tubes. An additional thermal annealing is performed, in order to study the influence of annealing on the phase content and stoichiometry of the CZTSe phases formed under these conditions. The structural characterization of the synthesized materials before as well as after annealing is carried out by powder X‐ray diffraction (PXRD), paying a special attention to the possibility of minimization the content of secondary phases. Wavelength dispersive X‐ray spectroscopy (WDX) is used to determine the chemical composition of the obtained phases, paying a special attention to the phase constituents as well as the evolution of the CZTSe phases after the additional annealing. A comparative study of the phase content of very far off‐stoichiometric CZTSe compounds is presented. The possible limits of the existence region of the kesterite CZTSe are discussed.

Cu2ZnSnSe4 (CZTSe) possess highly suitable optical and electronic properties for use as an absorber layer in thin film solar cells. CZTSe also has potential to achieve terawatt level solar energy production due to its inexpensive and abundant material constituents. Currently, fabricating CZTSe devices with the expected theoretical performance has not been achieved, making the growth and formation of CZTSe an interesting topic of research. In this work, a two-step vacuum fabrication process consisting of RF co-sputtering followed by reactive annealing was explored as a viable technique for synthesizing CZTSe thin films. Furthermore, the enhancement of the fabrication process by the incorporation of sodium during annealing was studied using a combinatorial approach. Film composition was analyzed using electron dispersive spectroscopy. Structure, phase morphology, and formation were determined using scanning electron microscopy, x-ray diffraction, atomic force microscopy and raman spectroscopy. Optical and electronic properties were characterized using UV-Vis and Voc were measurements under a one sun solar simulator. RF co-sputtering CuSe, ZnSe, and SnSe precursors produced films with good thickness uniformity, adhesion and stoichiometry control over 3 x 3 in2 substrates. Composition measurements showed that the precursor films maintained stability during an annealing process of 580o C for 20 minutes producing near stoichiometric CZTSe. However, grain size was small with an average diameter of 350 nm. The CZTSe film produced by this process exhibited a suitable absorption coefficient of > 104 cm-1 and aband gap near 1.0 eV. The film also produced an XRD pattern consistent with tetragonal CZTSe with no secondary phase formation with the exception of approximately 12.5 nm of interfacial MoSe2 formation at the back contact. The combinatorial investigation of the influence of sodium on CZTSe growth and morphology was achieved using a custom built constant withdraw shutter to evaporate NaF with a 0-60 nm thickness spread on the substrate prior to precursor sputtering. This experiment showed that the incorporation of NaF did enhance grain size; however, there was little correlation with initial NaF composition observed. It is concluded that NaF undergoes high degree of vapor transport and readily distributes nonuniformly throughout the film during the annealing process and also potentially escapes the annealing environment if not properly contained. An experiment on achieving Na incorporation by diffusion from a soda lime glass substrate resulted in a far more uniform enhancement of grain growth. The experiment also revealed that NaF greatly reduced precursor film adhesion to the substrate due to the hygroscopic nature of NaF. X-ray diffraction measurements also showed that the addition of the NaF layer was could potentially suppress the formation of MoSe2.

[EN] The earth abundant materiel Cu2ZnSnSe4 (CZTSe) is a promising quaternary semiconductor compound having kesterite symmetrical structure. CZTSe is considered as suitable absorber material for photovoltaic cell applications due to its optimum direct band gap. Cu2O/CZTSe/CdS/ZnO photovoltaic solar cell is proposed in this paper. Numerical modeling and analysis of the proposed cell is performed by using Solar Cell Capacitance Simulator (SCAPS). To analyze the effects on the cell performance different physical parameters are varied such as the thickness of the buffer and absorber layers and their carrier densities. Under 1.5 AM illumination condition, the proposed cell shows promising results and had achieved power conversion efficiency (PCE) of 25.95%, fill factor (FF) 85.24%, short circuit current (J(sc)) 31.41 mA/cm(2) and (V-oc) 0.97 V., This work was supported by Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat valenciana (Prometeus 2014/044).

Dissertação de Mestrado Integrado em Engenharia Física apresentada à Faculdade de Ciências e Tecnologia O quaternário Cu2ZnSnSe4 quaternário (CZTSe) é um material semicondutor promissor para camadas de absorção em células solares de filme fino devido ao seu band gap direto com energia por volta de 1 eV e alto coeficiente de absorção maior que 104 cm-1 [6]. A maior eficiência de conversão das células solares CZTSe alcançada até agora é superior a 11,6% [7]. No entanto, um fenómeno preocupante e comum em dispositivos fotovoltaicos com base em CZTSe é uma baixa tensão de circuito aberto em relação à energia de band gap. Uma razão plausível para tal pode ser uma redução no band gap efetivo devido a heterogeneidades na estrutura, fase ou composição na camada de absorção. Para obter um conhecimento detalhado sobre a influência das heterogeneidades de fase no desempenho das células solares, a compreensão dos limites de detecção dos métodos de investigação é essencial. Os limites de sensibilidade dos métodos utilizados convencionalmente, como difração de raios-X e espectroscopia de Raman, foram estudados recentemente [10]. Este trabalho tem com objetivo compreender os reais níveis de sensibilidade de XANES à presença de Cu2SnSe3 e ZnSe em Cu2ZnSnSe4, duas fases secundárias muito comuns para este material. Adicionalmente, foram investigados os efeitos de submeter amostras de CZTSe altamente não-estequiométricas contendo muitas fases secundárias a um segundo processo de recozimento térmico, com foco em mudanças nos seus conteúdos de fases e as composições das fases CZTSe.Para atingir o objetivo principal deste trabalho, foram utilizados dois conjuntos de amostras de pó policristalino. De modo a simular absorvedores CZTSe contendo uma fase secundária, o pó CZTSe monofásico foi misturado com quantidades determinadas de pó de fase secundária – Cu2SnSe3 ou ZnSe monofásicos – para obter uma série de calibração de misturas CZTSe contendo 1%, 2% 3%, 5%, 10% e 20% de fase secundária. Os dois conjuntos de misturas foram preparados em pellets e medidos por XANES em modo de transmissão nas K-edges de Se e Cu. Os dados das medições foram analisados com o programa ATHENA [21] usando um método de fitting por combinação linear (LCF).A caracterização de fase das amostras CZTSe recozidas foi realizada por difração de raios-X, enquanto a análise composicional foi realizada por espectroscopia de raios-X dispersiva de comprimento de onda.Os resultados obtidos mostraram que XANES é capaz de quantificar a fase secundária ZnSe a todas as concentrações dentro de uma pequena barra de erro. Com esta técnica, também foi possível detetar a fase Cu2SnSe3 até uma concentração de 5%. A investigação sobre a influência da estequiometria do standard de CZTSe e a adição de vários standards de fase secundária à análise LCF apresentaram resultados bastante inconclusivos, particularmente com as misturas de ZnSe, mas revelou a necessidade de uma investigação mais aprofundada sobre esses tópicos.Os resultados das técnicas aplicadas às amostras recozidas mostraram que o conteúdo de fases secundárias permaneceu idêntico na maioria das amostras e que a quantidade de fases CZTSe distintas não diminuiu em nenhuma delas, embora a composição destas tenha mudado em relação àquelas anteriormente presentes. No final, determinou-se que o recozimento não teve grandes benefícios no aumento da homogeneidade das amostras. The quaternary Cu2ZnSnSe4 (CZTSe) is a promising semiconductor material for absorber layers in thin film solar cells due to its direct band gap around 1 eV and high absorption coefficient larger than 104 cm-1 [6]. The highest conversion efficiency of CZTSe solar cells achieved so far is above 11.6% [7]. However, one troubling and common phenomenon in CZTSe-based photovoltaic devices is a low open-circuit voltage with respect to the band gap energy. A plausible reason for this could be a reduction in the effective band gap due to inhomogeneities in structure, phase, or composition in the absorber layer. To gain a detailed knowledge on the influence of phase inhomogeneities on the performance of solar cells, the understanding of detection limits of investigation methods is essential. The sensitivity limits of the conventionally used methods such as X-ray diffraction and Raman spectroscopy were studied recently [10]. This work aims to understand the real sensitivity levels of XANES to the presence of Cu2SnSe3 and ZnSe in Cu2ZnSnSe4, two very common secondary phases for this compound. Additionally, the effects of subjecting highly off-stoichiometric CZTSe samples containing many secondary phases to a second thermal annealing process were investigated, focusing on changes in their phase contents and the compositions of the CZTSe phases.To achieve the main purpose of this work, two sets of polycrystalline powder samples were used. So as to simulate secondary phase-containing CZTSe absorbers, single-phase CZTSe powder was mixed with determined amounts of secondary phase powder – single-phase Cu2SnSe3 or ZnSe – in order to obtain a calibration series of CZTSe mixtures containing 1%, 2%, 3%, 5%, 10% and 20% of secondary phase. The two mixture sets were prepared into pellets and measured by transmission mode XANES at the Se and Cu K-edges. Data from these measurements were analysed with the ATHENA program [21] using a linear combination fitting (LCF) method.The phase characterization of the re-annealed CZTSe samples was carried out by powder X-ray diffraction, while the compositional analysis was performed by wavelength-dispersive X-ray spectroscopy.Results obtained have shown that XANES is capable of quantifying the ZnSe secondary phase at all concentrations within a small error bar. With this technique, it was also possible to detect the Cu2SnSe3 phase down to 5% concentration. Investigation on the influence of the CZTSe standard’s stoichiometry and the addition of various secondary phase standards to the LCF analysis had largely inconclusive results, particularly with the ZnSe mixtures, but revealed the necessity for further investigation on these topics.Results from the techniques applied to the re-annealed samples showed that the secondary phase contents had remained identical in most samples and that the amount of distinct CZTSe phases did not decrease in any of them, although their composition had changed with respect to those previously present. In the end, it was determined that the annealing had no major benefits in increasing the homogeneity of the samples. Outro - ERASMUS

Bu tez çalışması Pamukkale Üniversitesi Bilimsel Araştırma Projeleri Koordinasyon Birimi tarafından 2013FBE021 nolu proje ile desteklenmiştir. Bu çalışmada; Cu2ZnSnSe4 (CZTSe) ince filmleri termal ve e-demeti buharlaştırma yöntemleri ile cam tabanlar üzerine büyütülmüştür. Üretilen filmler değişik sıcaklıklarda tavlanarak, yapısal özellikleri XRD, SEM ve Raman analizleri ile incelenmiştir. Yapısal analizler sonucunda iki farklı buharlaştırma yöntemi ile üretilen filmlerin kesterit yapıya sahip olduğu ve tavlama etkisine bağlı olarak daha düzenli yapıya geçerek tanecik boyutlarının arttığı gözlemlenmiştir. Filmlerin elektriksel parametreleri sıcaklığa bağlı iletkenlik ve Hail etkisi ölçümleri ile araştırılmıştır. Yapılan ölçümler sonucunda üretilen tüm filmlerin p-tipi iletkenliğe sahip olduğu, tavlama etkisi ile iletkenliklerinin ve taşıyıcı konsantrasyonlarının arttığı belirlenmiştir. Filmlerin ışığa karşı duyarlılıkları, sıcaklığa bağlı fotoiletkenlik ölçümleri ile incelenmiştir. Numunelerin fotoiletkenliğinin artan ışık şiddeti ile arttığı tespit edilmiştir. Optik soğurma ölçümleri ile filmlerin yasak enerji aralıkları araştırılmış ve tavlama etkisi ile birlikte yasak enerji aralıklarında düşüş gözlenmiştir. Mo/CZTSe/Metal yapısında Schottky diyotları üretilerek; gümüş (Ag), indiyum (In) ve alüminyum (Al) gibi farklı metallerin üst kontak olarak kullanılması ile bu diyotlarm doğrultucu özellikleri araştırılmıştır. Karanlık ortamda yapılan akım/kapasitans-voltaj ölçümleri ile diyotlarm elektriksel parametreleri belirlenmiştir. Al metali kullanılarak oluşturulan diyotun doğrultucu özellik göstermediği ve omik davranışa sahip olduğu belirlenmiştir. Ag ve In kontak kullanılarak üretilen Schottky eklemlerinin ise doğrultucu davranış sergilediği tespit edilerek, diyotlara ait bariyer yükseklikleri, taşıyıcı yoğunlukları ve kontak potansiyelleri hesaplanmıştır. Heteroeklem güneş hücreleri, Mo//?-CZTSe//?-CdS yapısında oluşturulmuştur. Karanlık ve aydınlık altında akım-voltaj ölçümleri ile üretilen güneş hücrelerinin diyot özelliği gösterdiği tespit edilmiştir. In this study, Cu2ZnSnSe4 (CZTSe) thin films have been produced on glass substrates by thermal and e-beam evaporation methods. The structural properties of deposited thin films, annealed at different temperatures, were examined through XRD, SEM and Raman analysis. Structural measurements have indicated that films were kesterite structure, the size of grains and crystallization of the films increased with increasing annealing temperatures. Hall effect and temperature dependent conductivity measurements were used to determine electrical parameters of the films. It is observed that all films having p-type conduction, carrier concentration and conductivity of the samples increases with increasing annealing temperature. In order to study photosensitivity of the films, photoconductivity measurements depending on light intensity were carried out. Photoconductivity of the films increases with increasing intensity of light. The optical band gaps of these films which were determined by optical absorption measurements indicated a slightly decrease with annealing. Schottky diode structures in the form of Mo/p-CZTSe/Metal were fabricated and rectifying properties of these devices were investigated with various top metal contacts such as Ag, A1 and In. The electrical parameters of the diodes were determined by dark current/capacitance-voltage measurements. It has been determined that the diode with A1 contacts has shown ohmic behavior. The rectifying behavior have been observed for Ag and In top contacts. The barrier heights, carrier densities and contact potentials of the diodes were also calculated. Heterostructures were obtained in the form of Mo//?-CZTSe/w-CdS. Dark and illuminated current-voltage measurements indicated that all samples have shown diode characteristics.

International audience; The CuZnSn (CZT) precursor thin films are grown by ion-beam sputtering Cu, Zn, Sn targets with different orders and then sputtering Se target to fabricate Cu2ZnSnSe4 (CZTSe) absorber thin films on molybdenum substrates. They are annealed in the same vacuum chamber at 400 °C. The characterization methods of CZTSe thin films include X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS) in order to study the crystallographic properties, composition, surface morphology, electrical properties and so on. The results display that the CZTSe thin films got the strongest diffraction peak intensity and were with good crystalline quality and its morphology appeared smooth and compact with a sequence of Cu/Zn/Sn/Se, which reveals that the expected states for CZTSe are Cu1+, Zn2+, Sn4+, Se2+. With the good crystalline quality and close to ideal stoichiometric ratio the resistivity of the CZTSe film with the sequence of Cu/Zn/Sn/Se is lower, whose optical band gap is about 1.50 eV. © 2017 Chinese Institute of Electronics.

Mestrado em Engenharia Física Os compostos designados como CZTS (Cu2ZnSnS4, Cu2ZnSnSe4 e Cu2ZnSn(Sx, Se1-x)4) constituem atualmente uma das maiores promessas para produção de células solar à escala de TW, devido ao uso de elementos abundantes e ambientalmente benignos, ao contrário dos compostos equivalentes no sistema CIGS. Contudo, ainda é necessário ultrapassar algumas barreiras de modo a atingir níveis de performance necessários para o desenvolvimento à escala industrial desta tecnologia. Uma tendência de investigação promissora consiste em introduzir uma gradação vertical no bandgap, ao longo da espessura da camada absorvente, através da variação do rácio S/(S + Se). Neste trabalho, camadas absorventes à base de CZTSxSe1-X foram produzidas pelo método de deposição de precursores empilhados por pulverização catódica seguido de sulfurização em H2S, em que o elemento Se é introduzido nos precursores por evaporação térmica. Duas configurações foram testadas: uma com a sequência de empilhamento ZnS/SnS2/Se/Cu repetida por vários períodos, e outra em que uma única camada de Se é introduzida no topo da sequência total de precursores. Usando este método, foram atingidos rácios S/(S + Se) aproximados desde 1 até perto de 0.5. A gradação da composição em profundidade foi parcialmente atingida, como é revelado através de Radiofrequency Pulsed Glow Discharge Time-of-Flight Mass Spectrometry (rf-PGDTOFMS). As camadas absorventes resultantes foram usadas para fabricar células com a estrutura SLG/Mo/CZTSSe/CdS/i-ZnO/ITO. A eficiência máxima atingida nos dispositivos fabricados foi 1.3%, numa camada com um rácio S/(S + Se) aproximado de 0.91, produzida a partir de precursores com Se no interior dos precursores empilhados. Microscopia de Eletrões Secundários (SEM), Espetroscopia de Dispersão de Energia (EDS), espetroscopia Raman e rf-PGD-TOFMS foram usados para caraterizar as amostras produzidas. As camadas absorventes produzidas, incluindo as com maior eficiência fotovoltaica, exibiram bolhas, rebentadas ou não rebentadas, e que rebentavam superficialmente ou rebentavam expondo o contacto inferior completamente, dependendo das condições de processamento. Este fenómeno foi estudado em detalhe, e novas observações não reportadas na literatura até ao momento foram encontradas, apontando para a possibilidade de controlar a formação de bolhas através do ajuste do perfil de sulfurização. Baseado nestes resultados, sugere-se uma revisão dos modelos propostos na literatura, e propõe-se um novo modelo baseado na volatilização de reagentes. CZTS-based compounds (Cu2ZnSnS4, Cu2ZnSnSe4 eCu2ZnSn(Sx, Se1-x)4) have become one of the major contenders for solar cell production at the TW level owing to the use of earth-abundant and environmentally benign elements, unlike their CIGS counterparts. However, some hurdles still need to be overcome in order to achieve performance levels necessary for industrial scalability. One promising trend of investigation consists in introducing a vertical bandgap grading along the thickness of the absorber by means of a variation of the S/(S + Se) ratio. In this work, CZTSxSe1-X absorbers were produced by the standard two-step process of sputtering deposition of a precursor stack followed by annealing in H2S, where the element Se was added in the precursor deposition stage using thermal evaporation. Two configurations were tested: one with the stacking sequence ZnS/SnS2/Se/Cu repeated for various periods, and another configuration where a single Se layer is evaporated on top of the multi-period precursor stack. Using this method, average S/(S + Se) ratios from 1 to close to 0.5 were demonstrated. Composition grading in depth was partially achieved as shown by Radiofrequency Pulsed Glow Discharge Time-of-Flight Mass Spectrometry (rf-PGD-TOFMS). The resulting absorbers were used to fabricate solar cells with the structure SLG/Mo/CZTSSe/CdS/i-ZnO/ITO. The highest efficiency achieved in the devices produced was 1.3%, using an absorber with an average S/(S + Se) of 0.91, produced from precursors with Se within the stack. Secondary Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Raman spectroscopy and rf-PGD-TOFMS was used to characterize the absorbers produced. The absorbers produced, including the highest performing devices, exhibited blisters, which would either burst or not burst, and burst either superficially or completely exposing the back contact, depending on processing conditions. This phenomenon was studied in detail, and new evidence was found, which has not been considered in literature so far, pointing to the possibility of significantly controlling blister formation by appropriately tuning the sulfurization profile. Based on these results, a review of the models proposed in literature to explain blister formation in CZTS is suggested, and a new model based on the volatilization of reactants is proposed.

Quaternary Cu2ZnSnSe4 is a promising low cost alternative absorber material for thin film solar cells. The current record conversion efficiency of 12.6% [1] for a Cu2ZnSn(S,Se)4 based thin film solar cell was reached when the polycrystalline CZTSSe absorber layer exhibits an off-stoichiometric composition. Deviations from stoichiometry in the absorber layer causes intrinsic point defects (vacancies, anti-site, interstitials) [2, 3] which determine significantly the electronic properties of the semiconductor, and in the efficiency of the solar cell device. Unfortunately, the current number of reported literature on intrinsic point defects of kesterites is very limited and mainly theoretical work. This work focuses on the synthesis and characterization of off-stoichiometric CZTSe. In order to perform experimental analysis of defect types and concentrations, polycrystalline powder samples have been synthesized by solid state reaction within different off- stoichiometric compositions suggested by [4, 5]. Chemical and structural characterization by WDX spectroscopy and XRD has been performed. The main results show, that all synthesized samples present kesterite type CZTSe with an off-stoichiometric composition as the main phase. Moreover, the formation of single phase off-stoichiometric kesterite type CZTSe has been observed. Further structural analyses by neutron powder diffraction experiments were carried out. As main outcome the cation distribution were determined, from which the intrinsic cation point defects and their concentrations have been evaluated. The occurrence of the corresponding off-stoichiometry type specific point defects could be proven. The results show, that it is possible to deduce the occurring point defect types from the chemical composition (cation ratios) of the kesterite phase. Additionally, the Cu-Zn disorder, which causes ZnCu and CuZn anti site defects, has been determined within all off-stoichiometric CZTSe phases., Quaternäre Cu2ZnSnSe4-Verbindungen (CZTSe) sind eine vielversprechende, kostengünstige Alternative als Absorberschichtmaterial in Dünnschichtsolarzellen. Der gegenwärtige Rekordwirkungsgrad von 12.6% [1] für eine Cu2ZnSn(S,Se)4-basierte Dünnschichtsolarzelle wurde für polykristalline Absorberschichten erreicht, die eine nicht-stöchiometrische Zusammensetzung aufweisen. Abweichungen von der Stöchiometrie führen zu intrinsischen Punktdefekten (Leerstellen, Substitionen, Zwischengitteratome) [2, 3], welche erheblich die elektronischen Eigenschaften und somit den Wirkungsgrad von Solarzellen bestimmen. Allerdings ist die Anzahl an Veröffentlichungen hinsichtlich intrinsischer Punktdefekte in Kesteriten sehr begrenzt und hauptsächlich theoretischer Natur. Diese Arbeit richtet sich auf die Synthese und Charakterisierung von nicht-stöchiometrischem CZTSe. Um experimentelle Analysen von Defekttypen und konzentrationen durchzuführen, wurden polykristalline Pulverproben innerhalb der von [4, 5] vorgeschlagenen nicht- stöchiometrischen Zusammensetzungen mittels Festkörperreaktion synthetisiert. Chemische sowie strukturelle Charakterisierung durch WDX-Spektroskopie und XRD ist durchgeführt worden. Die wichtigsten Ergebnisse zeigen, dass sämtliche synthetisierten Proben Kesterit-Typ CZTSe als Hauptphase mit einer nicht- stöchiometrischen Zusammensetzung aufzeigen. Darüber hinaus konnte die Bildung von einphasigen, nicht-stöchiometrischen Kesterit-Typ CZTSe beobachtet werden. Weitere, auf Pulver-Neutronenbeugungsexperimenten basierende, strukturelle Analysen wurden einbezogen. Als wichtigstes Ergebnis wurde die Kationenverteilung bestimmt, mit welcher die intrinsischen Punktdefekte sowie deren Konzentrationen ausgewertet worden sind. Das Auftreten korrespondierender, nicht-stöchiometrischer Typ-spezifischer Punktdefekte konnte nachgewiesen werden. Die Ergebnisse zeigen, dass es möglich ist, die auftretenden Punktdefekte von der chemischen Zusammensetzung (Kationenverhältnisse) der Kesteritphase abzuleiten. Zusätzlich ist die Cu-Zn- Unordnung, welche ZnCu- und CuZn- Fehlstellen hervorruft, in allen nicht- stöchiometrischen CZTSe-Phasen bestimmt worden

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In this study we present the synthesis of Cu2ZnSnSe4 (CZTSe) nanoparticles by microwave-assisted chemical synthesis employing organic solvents. The effect of reaction time, reactant concentration, solvent and additives (inorganic material) was studied on the structural and optical properties of the nanomaterials. The powder samples were analyzed by x-ray diffraction, Raman spectroscopy, x-ray energy dispersive spectroscopy and x-ray photoelectron spectroscopy. The results show that the synthesis performed with triethanolamine and deionized water is better than others solvents, producing nanocrystals of quaternary phase (CZTSe) with stoichiometric relations similar to the reported research in the literature, which falls in the range of Cu/(Zn+Sn): 0.8–1.0, Zn/Sn: 1.0–1.20. The nanoparticles of CZTSe synthesized in this study present desirable properties in order to use them in solar cell and photoelectrochemical cell applications.

In this work, we show a set of growth conditions, for the two step process, with which the growth of CZTSe is successful and reproducible. The properties of the best CTZSe thin films grown by this method were examined by SEM/EDS, XRD, Raman scattering, AFM/EFM, transmittance and reflectance measurements, photoluminescence (PL) measurements and hot point probe. A broad emission band was observed in the photoluminescence spectrum of the CZTSe thin film. The band gap energy was estimated to be around 1.05 eV at room temperature, using the transmittance and reflectance data, and CZTSe samples show p-type conductivity with the hot point probe. The different characterization techniques show that we could grow single phase CZTSe thin films with our optimized process conditions.

Facing growing energy demand and increasing concerns about climate change and finite energy sources, solar energy use should increase. The future of the different photovoltaic technologies obviously depends on their power conversion efficiency and cost (summarized by the ratio cost per watt), but also on the elements availability. Thin films of earth-abundant kesterite, Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) or Cu2ZnSn(S,Se)4 (CZTSSe), which can be manufactured with low-cost processes, are promising candidates for solar energy conversion at large scale.In this thesis, a copper tin and zinc precursor of controllable composition and thickness is electrodeposited on 15 × 15 cm² substrates. Electrodeposition is a process compatible with high throughput low-cost and safety industry requirements. The precursor is converted into a semiconductor by thermal treatments in presence of sulfur or selenium. The resulting Cu-Zn-SnS or Cu-Zn-Sn-Se layers should be uniform and have adequate properties (phases, composition and morphology) to produce high efficient solar cells. Full device processing, including the pn junction formation steps (wet chemical etching and buffer layer deposition) is also investigated in order to maximize device efficiency. The best CZTSe solar cell exhibits a 9.1% power conversion efficiency, setting a new record for kesterite solar cells produced by electrodeposition.; Dans un contexte général d’augmentation de la demande énergétique et de préoccupation croissante face au réchauffement climatique et à la limitation des ressources naturelles, l’utilisation d’énergie solaire devrait augmenter. L’avenir des différentes technologies photovoltaïques dépend évidemment de leur rendement de conversion photovoltaïque et de leur coût (ces deux paramètres peuvent être ramenés au coût par watt) mais aussi de la disponibilité des ressources. La kesterite, Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) ou Cu2ZnSn(S,Se)4 (CZTSSe), composée d’éléments abondants dans la croûte terrestre, et pouvant être fabriquée en couches minces avec des procédés à bas coûts, se positionne en candidat prometteur pour la conversion d’énergie solaire à grande échelle.Dans cette thèse, l’électro-dépôt, un procédé compatible avec des exigences industrielles de production de masse à bas coût et de sécurité, est utilisé pour déposer un précurseur de cuivre, étain et zinc sur des substrats de 15 × 15 cm², de composition et épaisseur contrôlables. Ce précurseur est ensuite converti en semiconducteur par traitement thermique en présence de soufre ou de sélénium. Les couches ainsi formées de Cu-Zn-Sn-S ou Cu-Zn-Sn-Se, doivent être uniformes et présenter les propriétés appropriées (phases, composition, morphologie) pour la fabrication de cellules solaires à haut rendement. Le procédé de fabrication de la cellule solaire complète, notamment les étapesqui interviennent dans la formation de la jonction p-n (décapage chimique et dépôt de couche tampon) est également optimisé pour maximiser les rendements. A l’issue de ces optimisations, un rendement de 9.1% est obtenu pour une cellule solaire CZTSe, un nouveau record pour les cellules solaires à base de kesterite fabriquées par électro-dépôt.

In this study Cu2ZnSnSe4 (CZTSe) solar cells have been formed by selenizing electrochemically deposited Cu-Zn-Sn (CZT) precursor. Two approaches have been presented for forming CZT precursor: a) co-deposition of Cu-Zn-Sn and stacked Cu, Sn, Zn layer deposition using flow cell. Deposition parameters (deposition potential, current density, electrolyte composition, flow rate) were optimized in order to obtain well-adherent to Mo substrate, uniform in thickness and composition CZT precursor layers. The detailed SEM combined with EDX investigation of CZT precursor morphology, cross-section and composition have been carried out. CZT precursors were preliminary annealed at 200 – 350 °C temperature in order to reduce film porosity and to form intermetallic compounds. The XRD and XRD in situ methods have been applied to investigate the formation of intermetallic compound of as-deposited and preheated CZT precursors. The influence of initial CZT composition and selenization conditions (temperature, duration, amount of Se) on the CZTSe morphology, phase composition and CZTSe solar cell performance has been investigated. Cu-poor, Zn-rich composition and preheating of CZT precursor was necessary to obtain relatively efficient CZTSe solar cells.

In this study Cu2ZnSnSe4 (CZTSe) solar cells have been formed by selenizing electrochemically deposited Cu-Zn-Sn (CZT) precursor. Two approaches have been presented for forming CZT precursor: a) co-deposition of Cu-Zn-Sn and stacked Cu, Sn, Zn layer deposition using flow cell. Deposition parameters (deposition potential, current density, electrolyte composition, flow rate) were optimized in order to obtain well-adherent to Mo substrate, uniform in thickness and composition CZT precursor layers. The detailed SEM combined with EDX investigation of CZT precursor morphology, cross-section and composition have been carried out. CZT precursors were preliminary annealed at 200 – 350 °C temperature in order to reduce film porosity and to form intermetallic compounds. The XRD and XRD in situ methods have been applied to investigate the formation of intermetallic compound of as-deposited and preheated CZT precursors. The influence of initial CZT composition and selenization conditions (temperature, duration, amount of Se) on the CZTSe morphology, phase composition and CZTSe solar cell performance has been investigated. Cu-poor, Zn-rich composition and preheating of CZT precursor was necessary to obtain relatively efficient CZTSe solar cells.

Double layer distribution exists in Cu2SnZnSe4 (CZTSe) thin films prepared by selenizing the metallic precursors, which will degrade the back contact of Mo substrate to absorber layer and thus suppressing the performance of solar cell. In this work, the double‐layer distribution of CZTSe film is eliminated entirely and the formation of MoSe2 interfacial layer is inhibited successfully. CZTSe film is prepared by selenizing the precursor deposited by electrodeposition method under Se and SnSex mixed atmosphere. It is found that the insufficient reaction between ZnSe and Cu‐Sn‐Se phases in the bottom of the film is the reason why the double layer distribution of CZTSe film is formed. By increasing Sn content in the metallic precursor, thus making up the loss of Sn because of the decomposition of CZTSe and facilitate the diffusion of liquid Cu2Se, the double layer distribution is eliminated entirely. The crystallization of the formed thin film is dense and the grains go through the entire film without voids. And there is no obvious MoSe2 layer formed between CZTSe and Mo. As a consequence, the series resistance of the solar cell reduces significantly to 0.14 Ω cm2 and a CZTSe solar cell with efficiency of 7.2% is fabricated.

The main objective of this PhD thesis was directed toward establishing and explaining the relationships between synthesis conditions of CZTSSe, its physical properties and performance of photovoltaic devices. To tackle this task, the first step is to understand the formation mechanism of the material in relation to the growth conditions. CZTSSe is synthesized by a two-step selenization process, where a first step of precursor deposition by PVD is followed by a second step of annealing. Different precursor stacking orders are studied in order to understand the sequence of reactions that, starting from their deposition, leads to the final CZTSSe layer. This study has required a strong effort on the material characterization at each step of the synthesis. The result demonstrates that in the case of our two-step process, the final material obtained after a selenization annealing at high temperature (570°C) for a long time (30 min) is independent of the precursor stacking order, but that the intermediate steps during the selenization process are strongly influenced by the position of the copper and tin layers in the precursor stack, . The possible benefits resulting from incorporation of sodium in CZTSSe are also studied. This work is carried out by synthesizing CZTSSe on different sodium-containing substrates: in this way sodium migrates from the substrates to the absorber. After quantification of Na in CZTSSe right after growth, the latter is characterized to evaluate its quality and employed in a full solar cell to check on its photovoltaic properties. Results demonstrate that, as for CIGS technology, sodium is beneficial for CZTSSe allowing increasing the open circuit voltage and efficiency. Molybdenum is the most used back contact in CZTSSe based solar cells. However, it has been suggested recently that Mo is not stable at the interface with CZTSSe. In addition, to the best of our knowledge, no experimental study has been carried out so far to test whether solar cells built on another back contact could exhibit better photovoltaic properties. For this purpose, various metals (Au, W, Pd, Pt, and Ni) are deposited on top of Mo, and it is demonstrated that it is possible to synthesize device-quality CZTSSe thin films on W, Au, and Pt back contacts. It is shown that that W and Au back contacts allow enhancing the photogenerated current, but that Mo remains the best back contact in terms of power conversion efficiency. The effects of [S]/([S]+[Se]) ratio tuning on CZTSSe based solar cell performances are studied by solar cell capacitance simulator (SCAPS) to find out the optimum absorber composition. The simulations lead to an efficiency of 16.5% (with open-circuit voltage of 0.56 V, short-circuit current of 37.0 mA/cm2 and fill factor of 79.0%) when the sulfur content is linearly decreased from the back contact towards the buffer layer. Based on these results, we propose that bandgap engineering based on the control of [S]/([S]+[Se]) ratio in the absorber is a powerful tool which allows increasing the performances of CZTSSe based solar cells without changing the absorber material quality.; L'objectif principal de cette thèse consiste à déterminer (et expliquer) les relations entre les conditions de synthèse des couches minces de Cu2ZnSn(Se,S)4 (CZTSSe), leurs propriétés physiques et les performances des dispositifs photovoltaïques. Le mécanisme de formation du matériau est étudié en fonction des conditions de croissance. Le CZTSSe est synthétisé par un procédé en deux étapes, où une première étape de dépôt des précurseurs sous vide est suivie d'une seconde étape de recuit sous atmosphère de sélénium. Différents ordres d'empilement des précurseurs sont étudiés afin de comprendre la séquence de réactions qui, à partir de leur dépôt, conduit à la couche finale de CZTSSe. Le résultat de cette étude montre que le matériau final obtenu après un recuit à haute température (570°C) et de longue durée (30 min) est indépendant de l'ordre de dépôt des précurseurs, mais que les étapes intermédiaires de formation du matériau sont fortement influencées par les positions respectives des couches de cuivre et d'étain. Les possibles implications bénéfiques de l'incorporation de sodium dans le CZTSSe sont également étudiées. Ce travail est réalisé en synthétisant la couche de CZTSSe sur différents substrats contenant diffèrents taux de sodium: de cette manière, pendant la synthèse, le sodium migre du substrat vers l'absorbeur. Après quantification du Na dans le CZTSSe juste après la croissance, le matériau est caractérisé afin d'évaluer sa qualité. Ensuite il est employé dans une cellule solaire complète pour vérifier ses propriétés photovoltaïques. Les résultats montrent que, comme dans le cas de la technologie CIGS, le sodium est bénéfique pour le CZTSSe, permettant l'augmentation de la tension à circuit ouvert et le rendement des cellules. Le molybdène est le contact arrière le plus utilisé pour les cellules solaires à base de CZTSSe. Cependant, il a été suggéré récemment que le Mo n'est pas stable à l'interface avec le CZTSSe. En outre, aucune étude expérimentale n'a été effectuée à ce jour pour tester si les cellules solaires construites sur un autre contact arrière pourraient présenter de meilleures propriétés photovoltaïques. Ainsi, divers métaux (Au, W, Pd, Pt et Ni) sont déposés sur le Mo et testés comme contacts arrières dans les cellules solaires à base de CZTSSe. Il est démontré qu'il est possible de synthétiser des couches minces de CZTSSe de qualité quand le tungstène, l'or et le platine sont employé comme contacts arrière. Il est observé que les contacts en W et Au permettent d'augmenter le courant photogénéré, mais aussi que le Mo reste le meilleur contact arrière du point de vue du rendement de conversion photovoltaïque. Les effets de la variation du rapport [S]/([S]+[Se]) sur les performances des cellules solaires à base de CZTSSe sont étudiés. Cette étude est effectuée par simulations des cellules solaires à base de CZTSSe, avec un ratio variable des éléments chalcogènes dans l'absorbeur, en ayant pour objectif la détermination de la composition optimale de l'absorbeur. Les simulations conduisent à un rendement de 16,5% (avec une tension en circuit ouvert de 0,56 V, courant de court-circuit de 37,0 mA/cm2 et un facteur de forme de 79,0%) lorsque la teneur en soufre est diminué linéairement à partir du contact arrière en direction de la couche tampon. Sur la base de ces résultats, nous proposons que l'ingénierie de bande interdite avec une variation du taux [S]/([S]+[Se]) dans l'absorbeur soit un moyen efficace qui permet d'augmenter les performances des cellules solaires à base CZTSSe sans nécessiter de changer la qualité même de l'absorbeur.

The ability of a photovoltaic cell to convert incident photons into electrical power is determined by the properties of its constituent materials and on their ability to function in concert with one another. Thin film solar cell materials benefit from the use of thin absorber layers that are relatively tolerant of a variety of structural defects. This allows for absorber layers to be made from polycrystalline films fabricated using raw materials that do not need to be refined to incredible levels of purity, as is generally required for single crystalline solar materials. Each of these traits represents significant logistical advantages during the industrial scale-up of thin film technologies, but they can be severely offset if scarce, expensive, or toxic materials are required during device fabrication. The various studies contained in the following chapters are dedicated to the exploration of next generation material systems that are being developed to resolve material issues that could potentially inhibit the large-scale implementation of existing thin film solar cell technologies.Silver nanowire networks stand as a potential replacement for transparent conductors made from doped metal oxide films. They exhibit excellent optical and electronic performance, and can be deposited in minutes from benign solutions with little damage to underlying device layers. When combined with an appropriately chosen matrix material to surround and encapsulate the wires, the resulting wire/matrix nanocomposite becomes a highly versatile electrode that can be integrated into a variety of thin film devices. Much of this dissertation is dedicated to the study and analysis of silver nanowire networks and partner materials and their applications in Cu(In,Ga)Se2 (CIGS) and amorphous silicon (a-Si) photovoltaics, starting from material synthesis and ink formulation and ending with device fabrication and characterization. In addition, the last chapter is dedicated to a discussion of heterojunction and space-charge formation in CZTSe solar cells, which is quickly becoming understood as a far more sensitive process than in its various chalcogenide analogues such as CIGS and CdTe. Together this set of materials would pave the way for the arrival of next generation thin film devices that can be fabricated quickly and with minimal reliance on indium, tellurium, or any other elements that would prevent their widespread commercial adoption.

Методами скануючої електронної мікроскопії, рентгеноструктурного аналізу, PIXI та RBS проведено дослідження тонкоплівкових зразків Cu2ZnSnSe4, отриманих співвипаровуванням компонентів з використанням електронно-променевої гармати. Аналіз дифрактограм показав, що плівки є практично однофазними і містять в основному сполуку CZTSe, яка має тетрагональну кристалічну гратку типу кістеріт. У зразках виявлена текстура росту [211]. Параметри гратки матеріалу змінювалися в діапазоні a = (0,56640-0,56867) нм, с = (1,13466-1,13776) нм, с/2a = 0,9983-1,0017, що добре корелює з довідковими даними по стабільній фазі сполуки CZTSe. Аналіз результатів PIXE, дозволив оцінити вплив умов росту на хімічний склад зразків, а також була побудована карта розподілу елементів по поверхні зразків. При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/37074 Методами сканирующей электронной микроскопии, рентгеноструктурного анализа, PIXI и RBS проведено исследование тонкопленочных образцов Cu2ZnSnSe4, полученных со-испарением компонентов с использованием электронно-лучевой пушки. Анализ дифрактограмм показал, что пленки являются практически однофазными и содержат в основном соединение CZTSe, имеющее тетрагональную кристаллическую решетку типа кистерит. В образцах обнаружена текстура роста [211]. Параметры решетки материала изменялись в диапазоне a = (0,56640-0,56867) нм, с = (1,13466-1,13776) нм, с/2a = 0,9983-1,0017, что хорошо коррелирует со справочными данными по стабильной фазе соединения CZTSe. Анализ результатов PIXE, позволил оценить влияние условий роста на химический состав образцов, а также была построена карта распределения элементов по поверхности образцов. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/37074 Cu2ZnSnSe4 thin films obtained by co-evaporation of components using an electron beam evaporation system were investigated by scanning electron microscopy, X-ray analysis, PIXI and RBS methods. The analysis of the diffraction patterns showed that the films are almost single-phased and contain mainly CZTSe compound, which has a tetragonal kesterite lattice type. The samples have textural growth of [211]. The lattice parameters of the material varied in the range of a = (0.56640-0.56867) nm, c = (1.13466-1.13776) nm, c/2a = 0,9983-1,0017 which correlate well with the reference data in a stable phase CZTSe compounds. From our PIXE analyses we assessed the influence of the growth conditions on the samples’ chemical composition and mapped the surface distribution. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/37074 Ця робота проводиться за підтримки Державного агентства України з питань науки, інновацій та інформатизації, а також Міністерства освіти і науки України (грант № 0113U000131) та Національного науково-дослідницького фонду Кореї (ННД) що фінансується Міністерством науки, ІКТ та майбутнього планування (MSIP) Корея (№ 2011-0019204).

The main objective of this PhD thesis was directed toward establishing and explaining the relationships between synthesis conditions of CZTSSe, its physical properties and performance of photovoltaic devices. To tackle this task, the first step is to understand the formation mechanism of the material in relation to the growth conditions. CZTSSe is synthesized by a two-step selenization process, where a first step of precursor deposition by PVD is followed by a second step of annealing. Different precursor stacking orders are studied in order to understand the sequence of reactions that, starting from their deposition, leads to the final CZTSSe layer. This study has required a strong effort on the material characterization at each step of the synthesis. The result demonstrates that in the case of our two-step process, the final material obtained after a selenization annealing at high temperature (570°C) for a long time (30 min) is independent of the precursor stacking order, but that the intermediate steps during the selenization process are strongly influenced by the position of the copper and tin layers in the precursor stack, . The possible benefits resulting from incorporation of sodium in CZTSSe are also studied. This work is carried out by synthesizing CZTSSe on different sodium-containing substrates: in this way sodium migrates from the substrates to the absorber. After quantification of Na in CZTSSe right after growth, the latter is characterized to evaluate its quality and employed in a full solar cell to check on its photovoltaic properties. Results demonstrate that, as for CIGS technology, sodium is beneficial for CZTSSe allowing increasing the open circuit voltage and efficiency. Molybdenum is the most used back contact in CZTSSe based solar cells. However, it has been suggested recently that Mo is not stable at the interface with CZTSSe. In addition, to the best of our knowledge, no experimental study has been carried out so far to test whether solar cells built on another back contact could exhibit better photovoltaic properties. For this purpose, various metals (Au, W, Pd, Pt, and Ni) are deposited on top of Mo, and it is demonstrated that it is possible to synthesize device-quality CZTSSe thin films on W, Au, and Pt back contacts. It is shown that that W and Au back contacts allow enhancing the photogenerated current, but that Mo remains the best back contact in terms of power conversion efficiency. The effects of [S]/([S]+[Se]) ratio tuning on CZTSSe based solar cell performances are studied by solar cell capacitance simulator (SCAPS) to find out the optimum absorber composition. The simulations lead to an efficiency of 16.5% (with open-circuit voltage of 0.56 V, short-circuit current of 37.0 mA/cm2 and fill factor of 79.0%) when the sulfur content is linearly decreased from the back contact towards the buffer layer. Based on these results, we propose that bandgap engineering based on the control of [S]/([S]+[Se]) ratio in the absorber is a powerful tool which allows increasing the performances of CZTSSe based solar cells without changing the absorber material quality., L'objectif principal de cette thèse consiste à déterminer (et expliquer) les relations entre les conditions de synthèse des couches minces de Cu2ZnSn(Se,S)4 (CZTSSe), leurs propriétés physiques et les performances des dispositifs photovoltaïques. Le mécanisme de formation du matériau est étudié en fonction des conditions de croissance. Le CZTSSe est synthétisé par un procédé en deux étapes, où une première étape de dépôt des précurseurs sous vide est suivie d'une seconde étape de recuit sous atmosphère de sélénium. Différents ordres d'empilement des précurseurs sont étudiés afin de comprendre la séquence de réactions qui, à partir de leur dépôt, conduit à la couche finale de CZTSSe. Le résultat de cette étude montre que le matériau final obtenu après un recuit à haute température (570°C) et de longue durée (30 min) est indépendant de l'ordre de dépôt des précurseurs, mais que les étapes intermédiaires de formation du matériau sont fortement influencées par les positions respectives des couches de cuivre et d'étain. Les possibles implications bénéfiques de l'incorporation de sodium dans le CZTSSe sont également étudiées. Ce travail est réalisé en synthétisant la couche de CZTSSe sur différents substrats contenant diffèrents taux de sodium: de cette manière, pendant la synthèse, le sodium migre du substrat vers l'absorbeur. Après quantification du Na dans le CZTSSe juste après la croissance, le matériau est caractérisé afin d'évaluer sa qualité. Ensuite il est employé dans une cellule solaire complète pour vérifier ses propriétés photovoltaïques. Les résultats montrent que, comme dans le cas de la technologie CIGS, le sodium est bénéfique pour le CZTSSe, permettant l'augmentation de la tension à circuit ouvert et le rendement des cellules. Le molybdène est le contact arrière le plus utilisé pour les cellules solaires à base de CZTSSe. Cependant, il a été suggéré récemment que le Mo n'est pas stable à l'interface avec le CZTSSe. En outre, aucune étude expérimentale n'a été effectuée à ce jour pour tester si les cellules solaires construites sur un autre contact arrière pourraient présenter de meilleures propriétés photovoltaïques. Ainsi, divers métaux (Au, W, Pd, Pt et Ni) sont déposés sur le Mo et testés comme contacts arrières dans les cellules solaires à base de CZTSSe. Il est démontré qu'il est possible de synthétiser des couches minces de CZTSSe de qualité quand le tungstène, l'or et le platine sont employé comme contacts arrière. Il est observé que les contacts en W et Au permettent d'augmenter le courant photogénéré, mais aussi que le Mo reste le meilleur contact arrière du point de vue du rendement de conversion photovoltaïque. Les effets de la variation du rapport [S]/([S]+[Se]) sur les performances des cellules solaires à base de CZTSSe sont étudiés. Cette étude est effectuée par simulations des cellules solaires à base de CZTSSe, avec un ratio variable des éléments chalcogènes dans l'absorbeur, en ayant pour objectif la détermination de la composition optimale de l'absorbeur. Les simulations conduisent à un rendement de 16,5% (avec une tension en circuit ouvert de 0,56 V, courant de court-circuit de 37,0 mA/cm2 et un facteur de forme de 79,0%) lorsque la teneur en soufre est diminué linéairement à partir du contact arrière en direction de la couche tampon. Sur la base de ces résultats, nous proposons que l'ingénierie de bande interdite avec une variation du taux [S]/([S]+[Se]) dans l'absorbeur soit un moyen efficace qui permet d'augmenter les performances des cellules solaires à base CZTSSe sans nécessiter de changer la qualité même de l'absorbeur.

Mestrado em Sistemas Energéticos Sustentáveis Neste trabalho pretende-se comparar filmes finos de Cu2ZnSnSe4, depositados por evaporação a vácuo e por pulverização catódica RF com magnetrão, usando precursores metálicos com camadas diferentes e selenizados a diferentes temperaturas. O estudo da estrutura, composição e morfologia dos filmes foi efetuado usando SEM/EDS, espectroscopia Raman e difração de raios-X. Os resultados obtidos comprovam a presença de Cu2ZnSnSe4 nos filmes depositados, sendo os melhores resultados obtidos para filmes para temperaturas de selenização mais elevadas e utilizando precursores com camadas de selénio depositadas antes e depois das camadas de cobre, zinco e estanho. The objective of this work is to compare Cu2ZnSnSe4 thin films deposited by evaporation and RF magnetron sputtering, utilizing metallic precursors with different layers and selenized at different temperatures. The study of the film’s structure, composition and morphology was performed by SEM/EDS measures, Raman spectroscopy and X-ray diffraction. The results prove the presence of Cu2ZnSnSe4 in the thin films, with better films for higher selenization temperatures and for films using precursors with selenium layers below and above the layers of copper, zinc and tin.

Neben mono- und polykristallinen Siliziumsolarzellen etablieren sich zunehmend Dünnschichtsolarzellen auf dem Markt. Auch wenn ihre Wirkungsgrade deutlich geringer sind, haben sie aufgrund ihrer niedrigeren Herstellungskosten, ihres geringen Gewichts und ihrer Flexibilität ein enormes Anwendungspotenzial.