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Volatile A-cation halide (AX) additives such as formamidinium chloride and methylammonium chloride have been widely employed for high-efficiency perovskite solar cells (PSCs). However, it remains unstudied how they influence the perovskite film stoichiometry and the solar cell performance and operational stability. Hereby, our work shows that over annealing of formamidinium chloride-containing perovskite films leads to a Pb-rich surface, resulting in a high initial efficiency, which however decays during maximum power point tracking (MPPT). On the contrary, perovskite films obtained by a shorter annealing time at the same temperature provide good stability during MPPT but a lower initial efficiency. Thus, we deduce that an optimal annealing is vital for both high efficiency and operational stability, which is then confirmed in the case where methylammonium chloride additive is used. With optimized perovskite annealing conditions, we demonstrate efficient and stable p-i-n PSCs that show a best power conversion efficiency of 20.7% and remain 90% of the initial performance after a 200 h MPPT at 60 °C under simulated 1 sun illumination with high UV content. Our work presents a comprehensive understanding on how volatile AX impacts perovskite film stoichiometry and its correlation to the device performance and operational stability, providing a new guideline for fabricating high-efficiency and operationally stable PSCs.

In situ phosphorus (P)-doped polycrystalline silicon (poly-Si) films by low pressure chemical vapor deposition (LPCVD) were studied in this work for the fabrication of poly-Si passivating contacts. In situ doping was targeted for enabling the full potential of the high-throughput LPCVD technique, as it could allow leaner fabrication of industrial solar cells featuring poly-Si passivating contacts than the more common ex situ doping routes. By careful optimization of the deposition temperature and the flows of the carrier gas (H-2) and the dopant precursor (PH3), high doping in the poly-Si layers was achieved with active P concentrations up to 1.3.10(20) cm(-3) . While reduction in the deposition rate (r(dep)) and thus in the throughput is a known problem when growing in situ P-doped films by LPCVD, this reduction could be limited, and the resulting r(dep) was equal to 0.078 nm/s. The developed poly-Si films were characterized both structurally and in terms of their passivation potential in poly-Si contacts. The latter yielded recombination current densities down to 1.5 fA/cm(2) in passivated (J(0, p)) and 25.6 fA/cm(2) in screen-printing metallized (J(0, m)) regions on saw-damage removed (SDR) Cz-Si surfaces, accompanied by a contact resistivity (rho(c,m)) of 4.9 m Omega.cm(2). On textured Cz-Si surfaces, the corresponding values were J(0, p) = 3.5 fA/cm(2), J(0,m )= 56.7 fA/cm(2), and rho(c,m) = 1.8 m Omega.cm(2). Optical impact of the developed poly-Si films was also assessed and a short circuit density loss of 0.41 mA/cm(2) is predicted per each 100 nm of poly-Si applied at the rear side of solar cells. The authors would like to acknowledge Rajiv Sharma from KU Leuven for his help with the interfacial oxide development, Sukhvinder Singh and Patrick Choulat from Imec for their help with the contact resistivity measurements and sample fabrication, Thomas Nuytten and Stefanie Sergeant from Imec for the Raman spectroscopy measurements, Bastien Douhard and Mustafa Ayyad from Imec for SIMS measurements, Maxim Korytov, Laura Nelissen, and Patricia van Marcke from Imec for the TEM specimen preparation and measurements, and Janusz Bogdanowicz from Imec for his help with the analysis of the Hall measurement data. This work was supported by the European Union’s Horizon2020 Programme for research, technological development, and demonstration [grant number 857793]; and by the Kuwait for the Advancement of Sciences [grant number CN18-15EE-01].

We demonstrate the scaling up of the perovskite photovoltaic technology with minimal performance losses by developing stable device architecture with industrially compatible processes. The monofacial (aperture area: 784 cm(2)) and bifacial (aperture area: 781 cm(2)) perovskite solar modules exhibit a power conversion efficiency of 13.1% and 11.9%, respectively. Moreover, the encapsulated bifacial mini-modules (aperture area: 4 cm(2)) retained similar to 92% of initial PCE after 1000 h of damp heat test. We would like to acknowledge Henri Fledderus and Ilker Dogan from TNO, Solliance for fruitful discussions on slot-die processing of perovskite. We would like to acknowledge Geert Doumen for the technical support provided for ITO sputtering.

Contactless plating with electroless solutions can provide self-aligned high-efficiency contacts with very low silver content, using simple and inexpensive equipment. With prior surface activation, it can even be used to metallize both sides of bifacial silicon solar cells simultaneously. However, we observe in such a coplating process with nickel, where surface activation is achieved by immersion plating and thickening by electroless plating, that V oc and fill factor can sometimes significantly decrease with immersion-plating time. To understand the reason for this electrical degradation, we studied the impact of immersion plating on the microstructure of the plated silicon surface. The evolution of the Si-Ni interface was studied by scanning and transmission electron microscopies, energy-dispersive X-ray analysis, secondary ion mass spectrometry, and scanning spreading resistance microscopy. Our attention focused on metal in-diffusion, silicon roughening and etching as the origin for increased recombination. Etching was found to have a significant impact on V oc. The thickness of N + Si etched during Ni deposition can in fact suppress in a few locations most of the field-effect passivation underneath the contacts. This means that a thicker surface field with doping beyond 1019/cm3 must be foreseen under the plated areas, or that the amount of Si lost in the reaction must be reduced. Our observations also confirm that immersion plating can hinder silicide formation and allow Ni in-diffusion, which may be a concern for reliability.

Volatile A-cation halide (AX) additives such as formamidinium chloride and methylammonium chloride have been widely employed for high-efficiency perovskite solar cells (PSCs). However, it remains unstudied how they influence the perovskite film stoichiometry and the solar cell performance and operational stability. Hereby, our work shows that over annealing of formamidinium chloride-containing perovskite films leads to a Pb-rich surface, resulting in a high initial efficiency, which however decays during maximum power point tracking (MPPT). On the contrary, perovskite films obtained by a shorter annealing time at the same temperature provide good stability during MPPT but a lower initial efficiency. Thus, we deduce that an optimal annealing is vital for both high efficiency and operational stability, which is then confirmed in the case where methylammonium chloride additive is used. With optimized perovskite annealing conditions, we demonstrate efficient and stable p–i–n PSCs that show a best power conversion efficiency of 20.7% and remain 90% of the initial performance after a 200 h MPPT at 60 °C under simulated 1 sun illumination with high UV content. Our work presents a comprehensive understanding on how volatile AX impacts perovskite film stoichiometry and its correlation to the device performance and operational stability, providing a new guideline for fabricating high-efficiency and operationally stable PSCs.

The implementation of anoxide layerwith contact openings to the Cu(In,Ga)Se2(CIGS) interfaces has become especially popular to reduce the recombination losses, resulting in a higher open-circuit voltage. While implementing this approach on the back surface is straightforward, it is more complicated for the front surface due to the roughness of the absorber as well as material selection constraints imposed by further processing steps. In this contribution, an AlOx/HfOxmulti-stack oxide layer with contact openings is applied between the CIGS and CdS layers. Two different approaches to create contact openings in multi-stack oxide layer are presented, and their advantages and disadvantages are investigated. In the bottom-up approach (BU), a NaCl salt pattern is created on the CIGS absorber surface, while in the top-down approach (TD), the pattern is created on the AlOxlayer surface. Time-resolved photoluminescence (TR-PL) shows that the multi-stack design improves the PL decay time regardless of the approach, but when the CdS layer is deposited, the PL decay time decreases. A more severe decrease is observed in case of the BU approach. Capacitance-Voltage measurements show that there is no impact on doping level when the NaCl pattern is created on an AlOxsurface. This work shows that any oxide material, even if not chemically resistant to the chemical bath deposition, can be applied at the CIGS/buffer layer interface, and additionally, any template can be used to create contact openings while preventing interaction between the material used for patterning and the CIGS, using the TD approach.

Passivating contacts consisting of heavily doped polycrystalline silicon (poly-Si) and ultrathin interfacial silicon oxide (SiOx) films enable the fabrication of high-efficiency Si solar cells. The electrical properties and working mechanism of such poly-Si passivating contacts depend on the distribution of dopants at their interface with the underlying Si substrate of solar cells. Therefore, this distribution, particularly in the vicinity of pinholes in the SiOx film, is investigated in this work. Technology computer-aided design (TCAD) simulations were performed to study the diffusion of dopants, both phosphorus (P) and boron (B), from the poly-Si film into the Si substrate during the annealing process typically applied to poly-Si passivating contacts. The simulated 2D doping profiles indicate enhanced diffusion under pinholes, yielding deeper semicircular regions of increased doping compared to regions far removed from the pinholes. Such regions with locally enhanced doping were also experimentally demonstrated using high-resolution (5-10 nm/pixel) scanning spreading resistance microscopy (SSRM) for the first time. The SSRM measurements were performed on a variety of poly-Si passivating contacts, fabricated using different approaches by multiple research institutes, and the regions of doping enhancement were detected on samples where the presence of pinholes had been reported in the related literature. These findings can contribute to a better understanding, more accurate modeling, and optimization of poly-Si passivating contacts, which are increasingly being introduced in the mass production of Si solar cells. This work was supported by the European Union’s Horizon2020 Programme for research, technological development, and demonstration [Grant 857793] and by the Kuwait Foundation for the Advancement of Sciences [Grant CN18- 15EE-01].

Perovskite/crystalline-silicon (c-Si) tandem solar cells offer a viable roadmap for reaching power conversion efficiencies beyond 30%. In this configuration, however, the silicon cell now mainly receives an infrared rich illumination spectrum where the absorption coefficient of silicon is poor. To boost the light absorption in this wavelength interval, transmitted through the top cell, a solution is to introduce a dedicated nanoscale texture on the front side of the silicon bottom cell and tweaking the optical elements in its design. These optical elements are manifold, with tunable geometrical dimensions, layer thicknesses, and refractive indices. For optically optimizing nanostructured silicon solar cells, electromagnetic wave solving methods, such as the rigorous coupled-wave analysis (RCWA), are normally used but they become computationally infeasible when several design variables are involved in an optimization problem. In this work, a natural selection algorithm, known as the genetic algorithm, is coupled with RCWA for extracting the optimal values of various design parameters in four-terminal perovskite/c-Si tandem devices in parallel. Both two-side-contacted and interdigitated back-contacted silicon heterojunction cell structures, featuring an inverse nanopyramid grating texture on the front, are optimized for five interdependent variables using a genetic algorithm for the bottom cell application and benchmarked against their random pyramid textured analogs. Our study shows that an optimized inverse nanopyramid grating texture can outperform the standard random pyramid texture when considering incidence angle variations. More importantly, the study illustrates how a genetic algorithm can support modeling complex solar cell structures with numerous degrees of freedom.

Carefully tailored periodic nanostructures on the light wavelength scale, such as diffraction gratings, benefit from wave optics for efficiently trapping the weakly absorbing infrared photons in crystalline-silicon (c-Si) absorbers. In contrast with the conventional random pyramid texture, diffraction gratings can be designed to target specific wavelength ranges by the selection of the grating pitch. Absorption enhancement at infrared wavelengths in a silicon solar cell is especially desired when it operates below a perovskite top cell in a tandem device. In this article, inverse nanopyramid gratings of 800 nm pitch are proposed as an alternative front-surface texture to random pyramids in silicon heterojunction devices with interdigitated back contacts that are to be used as bottom cells in four-terminal perovskite/c-Si tandem devices. By doing so, we report a short-circuit current density gain of 0.53 mA/cm 2 with respect to the random pyramid texturing for the bottom c-Si cell. The rationale to substitute random pyramids by inverse nanopyramid gratings is, however, not justified in single-junction operation despite achieving the power conversion efficiency of 22.3% since the degraded optical performance at shorter wavelengths offsets the absorption enhancement at longer wavelengths, resulting in similar levels of short-circuit current densities for both texture types. ispartof: Ieee Journal Of Photovoltaics vol:10 issue:3 pages:740-748 status: Published online

Thin (640 mV were achieved after the KF treatment. From SCAPS simulations and temperature dependent current voltage-measurements, it is concluded that the V-oc of these cells are limited by backcontact surface recombination and, thus, further improvements require passivation of the back contact. This work was supported by the European Union’s H2020 Research and Innovation Program under Grant 715027.

Herein, using the spin-coating process as a sodium pre-deposition technique for Cu(In,Ga)Se2, ultrathin film solar cells is discussed. Throughout this study, several challenges are detected to overcome, such as unevenly deposited salt layers and unplanned clusters (even islands) of sodium salts due to accumulation. The solar cell performances with the optimal and nonoptimal amounts of sodium are shared to assess the effect of varying sodium amounts on performance. The hyperspectral photoluminescence (PL) mapping and imaging and reflection measurements are also used to emphasize the importance of homogeneity of the sodium layer.

Poly-Si/SiOx passivating contacts enable the manufacturing of highly-efficient Si solar cells, but their fabrication commonly relies on an extra high-temperature process such as dopant diffusion or thermal annealing for achieving excellent passivation and contacting properties. This extra process is eliminated in the fired passivating contact (FPC) approach used for simplified fabrication of poly-Si/SiOx passivating contacts. Instead, FPCs rely on the thermal budget of the fast/short and high-temperature firing process used for metallization of solar cells to achieve similar final properties. Despite this, compatibility of FPCs with industrially viable metallization techniques has not been demonstrated yet, which is studied in this work for fire-through Ag screen-printing and Ni/Ag plating. With screen-printing, low recombination current density (J(0)) down to 4.9 fA/cm(2), low contact resistivity between the Ag contacts and the FPC (rho(c,m)) down to 7.2 m Omega.cm(2), and Ohmic transport through the FPC including the SiOx film were achieved using wet-chemically grown SiOx. Nevertheless, J(0) of metallized regions (J(0,m)) exceeded 1000 fA/cm(2). Reducing J(0,m) was attempted by mitigating the blistering observed in FPCs, but J(0,m) remained high. With Ni/Ag plating, excellent surface passivation with J(0) down to 2.7 fA/cm(2) and very low J(0,m) < 50 fA/cm(2) were achieved, but no Ohmic contacts could be obtained. Integration of screen-printed FPCs in large-area n-TOPCon solar cells was also demonstrated, yielding average efficiencies of 18.4%, limited mainly by the high J(0,) (m) and series resistance of the FPCs. The results presented reveal the challenges for the industrialization of FPCs and provide valuable insights for tackling these. The authors would like to acknowledge Patrick Choulat from Imec and Rajiv Sharma from KU Leuven for the valuable discussions and their help with the sample fabrication, Thomas Nuytten and Stefanie Sergeant from Imec for the Raman spectroscopy measurements, and Bastien Douhard and Mustafa Ayyad from Imec for the SIMS measurements. This work was supported by the European Union’s Horizon 2020 Programme for research, technological development, and demonstration [grant number 857793]; and by the Kuwait Foundation for the Advancement of Sciences [grant number CN18-15EE-01].

Interface recombination is one of the factors limiting the performance of Cu(In,Ga)Se2(CIGS). Especially in the absence of band grading at the front and rear surface, interface passivation approaches become important to improve device performance. The integration of an oxide layer as passivation layer at the front surface of the CIGS requires meticulous considerations in order not to impact the further steps of the solar cell production. In this article, a novel approach is reported to try to tackle the problem of interface recombination at the front surface of CIGS without affecting further solar cell production steps. In this approach, an Al2O3/HfO2multi-stack layer with contact openings is applied. NaCl template patterning with preliminarily selected parameters was used to create a homogeneous pattern of contact opening on the CIGS surface and allow the current flow in the device. After the removal of the NaCl islands, the holes in the multi-stack (openings) were visualized by scanning electron microscopy. In addition, energy-dispersive X-ray spectroscopy (EDS) was performed before and after chemical bath deposition of the buffer layer. The EDS result confirmed that the undesired etching of the Al2O3layer during buffer layer deposition was prevented by using a thin HfO2layer. Solar cells were produced by using preliminarily selected parameters for the multi-stack design. As a result, without having a significant negative impact on the solar cell parameters, a device design was achieved which is almost comparable with the reference device. In addition, options for future improvement and development are discussed.

Pure sulfide CIGS solar cells are interesting candidates for standalone solar cells or top cells in a tandem configuration. To understand the limits and improve the power conversion efficiency of these devices, a comprehensive approach aimed at composition, interface, and process engineering should be employed. Here, the latter was explored. Using a two-step fabrication technique and one-variable-at-a-time methodology, we found the four processing factors affecting the absorber the most. While two were already backed by the previous literature, we found new and statistical evidence for two other important factors as well. The impact of alkali barrier diffusion was also established with statistical significance and under various processing conditions. Furthermore, the absorber roughness for samples without a barrier indicated a significant negative linear correlation with the devices' efficiency. This contribution could aid engineers in more efficient process designs. European Union's Horizon 2020 Research and Innovation Program [640868]

In recent years, organometal halide perovskite based photovoltaics have attracted great interest for their high power conversion efficiency (PCE) potentially at low manufacturing cost. Despite the massive progress made by the community, the long-term performance stability and the manufacturability at large scale remain very challenging. In this work, we demonstrate a stable and scalable architecture for perovskite module fabrication. Thermal evaporation assisted 2-step approach is employed for the 1.53 eV perovskite deposition. For high throughput processing, NiOx by linear reactive sputtering is developed as the inorganic hole transport layer (HTL). PCE of 20% is achieved for the solar cell. Perovskite modules with monolithic series interconnected cells by picosecond laser scribing based on the developed cell stack are also fabricated. Above 80% of the initial efficiency is retained after 1000 hrs of thermal mono-stress at 85°C in N2 atmosphere.

Ultrathin Cu(In,Ga)Se-2 (CIGS) absorber layers of 550 nm were grown on Ag/AlOx stacks. The addition of the stack resulted in solar cells with improved fill factor, open circuit voltage and short circuit current density. The efficiency was increased from 7% to almost 12%. Photoluminescence (PL) and time resolved PL were improved, which was attributed to the passivating properties of AlOx. A current increase of almost 2 mA/cm(2) was measured, due to increased light scattering and surface roughness. With time of flight-secondary ion mass spectroscopy, the elemental profiles were measured. It was found that the Ag is incorporated through the whole CIGS layer. Secondary electron microscopic images of the Mo back revealed residuals of the Ag/AlOx stack, which was confirmed by energy dispersive X-ray spectroscopy measurements. It is assumed to induce the increased surface roughness and scattering properties. At the front, large stains are visible for the cells with the Ag/AlOx back contact. An ammonia sulfide etching step was therefore applied on the bare absorber improving the efficiency further to 11.7%. It shows the potential of utilizing an Ag/AlOx stack at the back to improve both electrical and optical properties of ultrathin CIGS solar cells. This research was funded by European Union H2020 research and innovation program grant number 715027.

Perovskite solar cells have shown their potential for multijunction applications due to their tunable bandgap. This research focuses on triple cation (3C) wide bandgap perovskites ranging from 1.6 to 1.76 eV, an ideal bandgap choice for 2-terminal tandems. The bandgap is changed via the X-site substitution of iodine (I) with bromine (Br) and via cation substitution, with various concentrations of cesium (Cs), methylammonium (MA), and formamidinium (FA). As a result, it is seen that cation engineering is a viable solution to fine-tune the bandgap and prevent a photoinduced segregation. Moreover, a champion efficiency of 18.3% is reported with a 1.67 eV bandgap.

A simplified Cu(In, Ga)Se-2 (CIGS) solar cell structure based on a 500 nm thin CIGS layer is presented. The absorber layers are grown with a single-stage coevaporation process, and various KF post-deposition treatments (KF-PDT) are performed. The KF-PDT leads to an efficiency increase from 7% to 12%. For all cells an increase in open circuit voltage (V-oc) and fill factor is measured, which is attributed to an improved pn junction. By changing the annealing conditions, an additional V-oc increase is measured. This increase is attributed to the reduction of light-induced defects at the CIGS/CdS interface in addition to the improved pn junction. A reduction of defects is confirmed by reduced sub band gap emission in the photoluminescence spectra, an increased decay time, and increased quasi Fermi level splitting. With SCAPS the results are simulated, and it is concluded that after KF-PDT the V-oc is limited to 640 mV due to recombination at the back contact. A higher V-oc can then only be achieved by applying a passivation layer at the back. There are no indications that the single-stage process is limiting the efficiency, revealing the potential of the proposed simplified CIGS structure and the importance of interfaces for ultrathin CIGS solar cells. J. de Wild, D.G. Buldu, T. Kohl, G. Birant, and B. Vermang received funding from the European Union’s H2020 research and innovation program under grant agreement no. 715027.

Further increasing the conversion efficiency of silicon solar cells by advanced solar cell concepts like SHJ (Silicon Hetero-Junction), PERT (Passivated Emitter Rear Totally diffused), IBC (Interdigitated Back-Contact), requires a highly controlled silicon surface in terms of metal impurity density. The goal of this study is investigating the deposition property of different metals in acidic cleaning solutions and consequently determining the impact of these impurities on the effective minority lifetime of the crystalline silicon solar cell material. The deposition behaviour of impurities is mathematically described with an adsorption isotherm theory. Once attached at the silicon surface, the metal impurity can diffuse into the silicon bulk material during a high temperature process step like diffusion, passivation or contact annealing (firing). First, we have studied the adsorption isotherm behaviour of prominent metal impurities (Fe, Cu, Ti, Co, Cr and Zn) in acidic liquid onto a silicon surface. Moreover, the impact of metal impurities on effective minority carrier lifetime in commercially available n-type Cz-silicon (3–5 Ω cm, 239 cm2) is determined. From controlled contamination experiments we can extract an exchange volume, that provides the minimum amount on wet chemical cleaning solution that is required to clean a silicon surface from a given high metal impurity level to a specified low metal impurity level. This exchange volume plays a crucial role by defining feed and bleed recipes on wet chemical cleaning tanks in solar cell manufacturing. A second parameter extracted is the effective minority carrier lifetime degradation of the metal impurities. After deposition on the surface, the impurities are driven into the silicon bulk by high temperature processes. Depending on the lifetime degradation capacity, a relation of effective minority carrier lifetime versus surface contamination level could be identified for each metal impurity. We found Co, Fe and Cu having a strong impact on effective minority carrier lifetime degradation, e.g. 2e10/cm2 Fe surface concentration can reduce the effective minority carrier lifetime by 75%, while Ti, Zn and Cr are more moderate and only high surface concentrations above 1e12/cm2 lead to effective minority carrier lifetime degradation of more than 20% compared to the non-contaminated wafers.

© Copyright 2019 American Chemical Society. Low contact resistivity ( c ) and low recombination current density at the metallized area (J 0,metal ) are the key parameters for an electron-selective contact in solar cells, and an i-a-Si:H/TiO x /low work function metal (ATOM) structure could satisfy these criteria. In this work, to achieve strong downward band bending, an Yb ( = 2.5-2.6 eV)/Ag stack is used. Moreover, the impact of (1) substrate topography (flat or textured), (2) TiO x thickness, and (3) Ti precursor (TTIP vs TDMAT) on the ATOM contact performance is investigated. The results show that the ATOM contact is relatively insensitive to the surface topography and to the Ti precursors (TTIP or TDMAT) used for the atomic layer deposition (ALD) of TiO x . However, the TiO x thickness has a significant impact on the c and marginally on the J 0,metal of the ATOM contact. For all topography cases and Ti precursors, 1 nm thick TiO x results in the lowest c value, most likely due to E F,metal depinning. In the silicon heterojunction solar cell, this ATOM contact (i-a-Si:H/TiO x /Yb/Ag) yields a solar cell efficiency of 19.2% with a high V OC of 723 mV without the need of a doped n-a-Si:H layer. Concerning the thermal stability of these contacts, TEM images confirm that Yb does not diffuse into the i-a-Si:H layer after an annealing at 180 °C for 30 min thanks to the TiO x layer behaving as a diffusion barrier. 98% of the initial solar cell efficiency is preserved even after successive annealing treatments at 150 and 175 °C, which are values in the same temperature range used in the module lamination and the sintering of the printed Ag. These results in combination with the demonstrated efficiency underline that the ATOM contact is a promising route to realize high-efficiency solar cells. ispartof: ACS APPLIED ENERGY MATERIALS vol:2 issue:2 pages:1393-1404 status: published

© 2018 Elsevier Ltd The global shift towards renewable energy production combined with the expected penetration of electric cars, increasing energy usage of cloud computing centers and the transformation of the electricity grid itself towards the “Smart Grid” requires novel solutions on all levels of energy production and management. Forecasting of energy production especially will become a major component for design and operation in all temporal and spatial scales, creating opportunities for optimized control of energy storage, local energy exchange etc. To this end, a method for the creation of detailed and accurate energy yield forecasts for PV installations is presented. Based on sky-imager information and using tailored neural networks, highly detailed energy yield forecasts are produced for a monitored test installation, for horizons up to 15 min and with a resolution of 1 s. Thermal effects are included in the calculations and error propagation is minimized by reducing the modeling steps. The described method manages to outperform state of the art models by up to 39% in forecast skill, while at the same time retaining temporal resolutions that enable control schemes and energy exchange in a local scale. ispartof: RENEWABLE ENERGY vol:130 pages:122-129 status: published

A new multi-stack approach with contact openings was investigated for front surface of Cu(In,Ga)Se 2 thin film solar cells. In this multi-stack design, a thin HfO x layer was used to protect a thicker AlO x layer from the presence of ammonia in the chemical bath deposition. The contact openings were created by using alkali solution. The lifetime decay was improved by implementing multi-stack passivation layer between CIGS/buffer layer interface. It was shown that open circuit voltage was increased by up to 30mV.

In this contribution, a cost- and time- effective contacting approach is presented for dielectric-based rear surface passivation layers up to 30 nm. Nano-size and homogenously distributed openings are realized in AlOx passivation layer by selenization of LiF salt on top, and monitored via SEM. Further, this layer was implemented into sub-micron thick CIGS solar cells. Consequently, contact openings facilitate the current collection through the dielectric layer up to 30 nm thick. However, solar cell parameters remain the same, even worse than the reference. Thus, this approach is still open for optimizations.

In modern Cu(In,Ga)Se2 (CIGS) solar cell production, alkali-poor substrates are becoming increasingly common. Thus, understanding the effect of alkali atoms on the growth of the CIGS absorber has become crucial. We studied this impact by comparing the bias dependent admittance spectroscopy response of CIGS solar cells grown with varying amounts of sodium using two different growth processes. The absence of sodium led to an intense response which is progressively replaced by other response domains as the sodium supply increases. We linked these new domains to Na accumulation and a resulting increase in band bending at the CIGS/CdS interface.

In Cu(In,Ga)Se2(CIGS) thin-film solar cells, interface recombination is one of the most important limiting factors with respect to device performance. Herein, metal–insulator–semiconductor samples are used to investigate and compare the passivation effects of Al2O3and HfO2at the interface with CIGS. Capacitance–voltage–frequency measurements allow to qualitatively and quantitatively assess the existence of high negative charge density (Qf ≈ −1012 cm−2) and low interface-trap density (Dit ≈ 1011 cm−2 eV−1). At the rear interface of CIGS solar cells, these, respectively, induce field-effect and chemical passivation. A trade-off is highlighted between stronger field-effect for HfO2and lower interface-trap density for Al2O3. This motivates the usage of Al2O3to induce chemical passivation at the front interface of CIGS solar cells but raises the issue of its processing compatibility with the buffer layer. Therefore, an innovative Al2O3/HfO2multistack design is proposed and investigated for the first time. Effective chemical passivation is similarly demonstrated for this novel design, suggesting potential decrease in recombination rate at the front interface in CIGS solar cells and increased efficiency. 300 °C annealing in N2environment enable to enhance passivation effectiveness by reducingDitwhile surface cleaning may reveal useful for alternative CIGS processing methods.

ispartof: Progress In Photovoltaics vol:29 issue:5 pages:1-9 status: Published online

This work presents a novel method of local contact openings formation in an aluminum oxide (Al2O3) rear surface passivation layer by the selenization of the lithium fluoride (LiF) salt on top of the Al2O3for ultra-thin copper indium gallium (di)selenide (CIGS) solar cells (SCs). This study introduces the potentially cost-effective, fast, industrially viable, and environmentally friendly way to create the nano-sized contact openings with the homogeneous distribution in the thick, i.e. up to 30 nm, Al2O3passivation layer. The passivation layer is deposited by atomic layer deposition, while the LiF layer is spin-coated. Selenization is done in the H2Se atmosphere and the optimal process parameters are deduced to obtain nano-sized and uniformly allocated openings as confirmed by scanning electron microscopy images. The contact openings were produced in the different thicknesses of the alumina layer from 6 nm to 30 nm. Furthermore, the Al2O3rear surface passivation layer with the contact openings was implemented into ultra-thin CIGS SC design, and one trial set was produced. We demonstrated that the created openings facilitate the effective current collection through the dielectric Al2O3layer up to 30 nm thick. However, the upper limit of Al2O3thickness in which the contact openings can be created by the described method is not established yet. The produced passivated CIGS SCs show increased external quantum efficiency response due to the optical enhancement of the passivated cells. However, the production of SCs on the Al2O3passivation layer with the openings created by selenization of LiF is not optimized yet.