Opto‐electrical modelling and optimization study of a novel IBC c‐Si solar cell

Interdigitated back contact (IBC) crystalline silicon (c‐Si) solar cells are attracting a lot of attention because of their capability to reach world record conversion efficiency. Because of the relatively complex contact pattern, their design and optimization typically require advanced numerical simulation tools. In this work, a TCAD‐based simulation platform has been developed to account accurately and in detail the optical and passivation mechanisms of front texturization. Its validation has been carried out with respect to a novel homo‐junction IBC c‐Si solar cell based on ion implantation and epitaxial growth, comparing measured and simulated reflectance, transmittance, internal quantum efficiency, external quantum efficiency spectra, and current density–voltage characteristics. As a result of the calibration process, the opto‐electrical losses of the investigated device have been identified quantitatively and qualitatively. Then, an optimization study about the optimal front surface field (FSF) doping, front‐side texturing morphology, and rear side geometry has been performed. The proposed simulation platform can be potentially deployed to model other solar cell architectures than homo‐junction IBC devices (e.g., passivated emitter rear cell, passivated emitter rear locally diffused cell, hetero‐IBC cell). Simulation results show that a not‐smoothed pyramid‐textured front interface and an optimal FSF doping are mandatory to minimize both the optical and the recombination losses in the considered IBC cell and, consequently, to maximize the conversion efficiency. Similarly, it has been showed that recombination losses are affected more by the doping profile rather than the surface smoothing. Moreover, the performed investigation reveals that the optimal FSF doping is almost independent from the front texturing morphology and FSF passivation quality. According to this result, it has been demonstrated that an IBC cell featuring an optimal FSF doping does not exhibit a significant efficiency improvement when the FSF passivation quality strongly improves, proving that IBC cell designs based on low‐doped FSF require a very outstanding passivation quality to be competitive. Deploying an optimization algorithm, the adoption of an optimized rear side geometry can potentially lead to an efficiency improvement of about 1%_abs as compared with the reference IBC solar cell. Further, by improving both emitter and c‐Si bulk quality, a 22.84% efficient solar cell for 280‐μm thick c‐Si bulk was simulated. Copyright © 2017 John Wiley & Sons, Ltd.     

Enhanced lateral current transport via the front N+ diffused layer of n‐type high‐efficiency back‐junction back‐contact silicon solar cells

N‐type back‐contact back‐junction solar cells were processed with the use of industrially relevant structuring technologies such as screen‐printing and laser processing. Application of the low‐cost structuring technologies in the processing of the high‐efficiency back‐contact back‐junction silicon solar cells results in a drastic increase of the pitch on the rear cell side. The pitch in the range of millimetres leads to a significant increase of the lateral base resistance. The application of a phosphorus doped front surface field (FSF) significantly reduces the lateral base resistance losses. This additional function of the phosphorus doped FSF in reducing the lateral resistance losses was investigated experimentally and by two‐dimensional device simulations. Enhanced lateral majority carrier's current transport in the front n⁺ diffused layer is a function of the pitch and the base resistivity. Experimental data show that the application of a FSF reduces the total series resistance of the measured cells with 3.5 mm pitch by 0.1 Ω cm² for the 1 Ω cm base resistivity and 1.3 Ω cm² for the 8 Ω cm base resistivity. Two‐dimensional simulations of the electron current transport show that the electron current density in the front n⁺ diffused layer is around two orders of magnitude higher than in the base of the solar cell. The best efficiency of 21.3% was obtained for the solar cell with a 1 Ω cm specific base resistivity and a front surface field with sheet resistance of 148 Ω/sq. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental and simulated analysis of front versus all‐back‐contact silicon heterojunction solar cells: effect of interface and doped a‐Si:H layer defects

Front silicon heterojunction and interdigitated all‐back‐contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high efficiency and low cost because of their good surface passivation, heterojunction contacts, and low temperature fabrication processes. The performance of both heterojunction device structures depends on the interface between the crystalline silicon (c‐Si) and intrinsic amorphous silicon [(i)a‐Si:H] layer, and the defects in doped a‐Si:H emitter or base contact layers. In this paper, effective minority carrier lifetimes of c‐Si using symmetric passivation structures were measured and analyzed using an extended Shockley–Read–Hall formalism to determine the input interface parameters needed for a successful 2D simulation of fabricated baseline solar cells. Subsequently, the performance of front silicon heterojunction and IBC‐SHJ devices was simulated to determine the influence of defects at the (i)a‐Si:H/c‐Si interface and in the doped a‐Si:H layers. For the baseline device parameters, the difference between the two device configurations is caused by the emitter/base contact gap recombination and the back surface geometry of IBC‐SHJ solar cell. This work provides a guide to the optimization of both types of SHJ device performance, predicting an IBC‐SHJ solar cell efficiency of 25% for realistic material parameters. Copyright © 2013 John Wiley & Sons, Ltd.     

Nanostructured Si/Organic Heterojunction Solar Cells with High Open‐Circuit Voltage via Improving Junction Quality

Nanostructured silicon (Si) can provide improved light harvest efficiencies in organic‐Si heterojunction solar cells due to its low light reflection ratio compared with planar one. However, the associated large surface/volume ratio of nanostructured Si suffers from serious surface recombination as well as poor adhesion with organics in organic‐Si heterojunction solar cells, which leads to an inferior open‐circuit voltage (V_oc). Here, we develop a simple and effective method to suppress charge recombination as well as enhancing adhesion force between nanostructured Si and organics by incorporating a silane chemical, namely 3‐glycidoxypropyltrimethoxydsilane (GOPS). GOPS can chemically graft onto nanostructured Si and improve the aqueous organic wetting properties, suppressing surface charge recombination velocity dramatically. In addition, this chemically grafted layer can enhance adhesion force between organics and Si. In such a way, a record V_oc of 640 mV associated with a power conversion efficiency of 14.1% is obtained for organic‐nanostructured Si heterojunction devices. These findings suggest a promising approach to low‐cost and simple fabrication for high‐performance organic‐Si solar cells.     

Highly Efficient Hybrid Solar Cells Based on an Octithiophene–GaAs Heterojunction

We report a new type of hybrid heterojunction solar cell based on rod‐like octithiophene (8T) as the organic p‐type semiconductor and GaAs(111) as the inorganic n‐type semiconductor. By using a semitransparent gold layer as the front contact deposited onto the 8T films, solar‐energy conversion efficiencies of up to 4.2 % could be obtained. The reduction in the contact resistance at the Au/8T interface induced by iodine doping is found to be a very crucial factor for the high efficiency. Furthermore, we demonstrate that hybrid solar cells can be successfully used to investigate the photovoltaic properties of organic semiconductors in detail. By means of external quantum efficiency (EQE) measurements, the influence of film morphology on the photocurrent collection length in 8T films is studied. The results show that, in hybrid solar cells using highly ordered microcrystalline 8T films, an active contribution of the organic‐layer semiconductor to the total photocurrent exists. A very large photocurrent collection length of up to 100 nm has been estimated from EQE measurements, indicating that exciton diffusion is very efficient in microcrystalline 8T. On the other hand, the use of nanocrystalline 8T leads to high photocurrent losses in the organic part of the hybrid solar cell. The strong influence of the film morphology on the photocurrent collection in 8T is attributed to a reduction in the exciton diffusion length due to a high trap density in nanocrystalline 8T films. Thus, our results reveal the importance of high crystalline order for obtaining efficient photocurrent collection in 8T films.     

8% Efficient thin‐film polycrystalline‐silicon solar cells based on aluminum‐ induced crystallization and thermal CVD

A considerable cost reduction could be achieved in photovoltaics if efficient solar cells could be made from polycrystalline‐silicon (pc‐Si) thin films on inexpensive substrates. We recently showed promising solar cell results using pc‐Si layers obtained by aluminum‐induced crystallization (AIC) of amorphous silicon in combination with thermal chemical vapor deposition (CVD). To obtain highly efficient pc‐Si solar cells, however, the material quality has to be optimized and cell processes different from those applied for standard bulk‐Si solar cells have to be developed. In this work, we present the different process steps that we recently developed to enhance the efficiency of pc‐Si solar cells on alumina substrates made by AIC in combination with thermal CVD. Our present pc‐Si solar cell process yields cells in substrate configuration with efficiencies so far of up to 8·0%. Spin‐on oxides are used to smoothen the alumina substrate surface to enhance the electronic quality of the absorber layers. The cells have heterojunction emitters consisting of thin a‐Si layers that yield much higher V_oc values than classical diffused emitters. Base and emitter contacts are on top of the cell in interdigitated finger patterns, leading to fill factors above 70%. The front surface of the cells is plasma textured to increase the current density. Our present pc‐Si solar cell efficiency of 8% together with the fast progression that we have made over the last few years indicate the large potential of pc‐Si solar cells based on the AIC seed layer approach. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation of alternative window materials for GaAs solar cells

The optimum window material for surface passivation of GaAs solar cells is investigated using theoretical analysis of optical losses due to window bandgap energy and thickness. A simplified expression is developed to calculate the effective surface recombination velocity in terms of lattice mismatch between the window layer and GaAs, which suggests using a window material with and indirect bandgap energy greater than 2.0 eV, a thickness of less than 0.05 μm, and a lattice mismatch of less than 0.05%. Experimental GaAs solar cells were fabricated and quantum efficiency measurements were made using no window (bare GaAs), Al_0.7Ga_0.3As, Na₂S, and ZnSe/Na₂S windows. The Al_0.7Ga_0.3As and Na₂S windows are shown to passivate the GaAs surface and reduce the surface recombination velocity to less than 10⁵ cm/s, while the ZnSe encapsulating layer was used to permanently maintain the temporary surface passivation effects from Na₂S     

Influence of series resistance on guidelines for manufacture of concentrator p‐on‐n GaAs solar cells

This paper deals with the determination of the main factors influencing series resistance in p‐on‐n GaAs solar cells working at concentration levels of 1000 suns or higher. Prior to this analysis, a comparison between different front metal grid geometries is presented to show the strong influence that the front grid component of series resistance exerts on its global value. Once the inverted square grid geometry is selected, a detailed analysis of the different components of series resistance is carried out. For this purpose, a multidimensional optimisation of the whole GaAs solar cell (antireflecting coatings, series resistance and semiconductor structure) has been used for the first time. In order to orient the manufacture of very high concentrator GaAs solar cells, recommendations on the threshold values of solar cell size, specific p‐ and n‐contact resistances, thickness of the front metal grid and both doping level and thickness of the substrate are formulated. Several traditional ideas on the influence of these parameters are questioned. Copyright © 2000 John Wiley & Sons, Ltd.     

A high‐efficiency LPE GaAs solar cell at concentrations ranging from 2000 to 4000 suns

III–V solar cells for terrestrial concentration applications are currently becoming of greater and greater interest. From our experience, concentrations higher than 1000 suns are required with these cells to reduce PV electricity cost to such an extent that this alternative could become cost competitive. In this paper, a single‐junction p/n GaAs solar cell, with efficiencies of 23ċ8 and 22ċ5% at concentration ratios of 2700 and 3600 suns respectively, is presented. This GaAs solar cell is well suited for use with non‐imaging optical concentrators, which possess a large aperture angle. Low‐temperature liquid phase epitaxy (LTLPE) has been the growing technique for the semiconductor structure as an attempt to use a simplified, cheap and clean technique, within a renewable energy perspective. The GaAs solar cell presented is compared with the highest efficiency tandem solar cells at concentration levels exceeding 1000 suns. The GaAs solar cell performance maintains high efficiencies up to 4000 suns, while tandem cells seem to drop very quickly after reaching their maximum. Therefore, single‐junction GaAs solar cells are a good candidate for operating at very high concentrations, and LPE is able to supply these high‐quality solar cells to work within terrestrial concentration systems, the main objective of which is the reduction of PV electricity costs. Copyright © 2003 John Wiley & Sons, Ltd.     

Optimization and characterization of amorphous/crystalline silicon heterojunction solar cells

Amorphous hydrogenated silicon/crystalline silicon (a‐Si:H/c‐Si) heterojunction solar cells are investigated and optimized with regard to efficiency and simplicity of processing. Starting with a survey of a‐Si:H/c‐Si heterojunction solar cell results from the literature, we describe the fabrication steps of our a‐Si:H/c‐Si technology and analyze the electronic device properties by quantum efficiency, current–voltage, admittance, and capacitance–voltage measurements. The open‐circuit voltage and the fill factor of the a‐Si:H/c‐Si heterojunction solar cells under investigation are limited by recombination in the neutral zone of the crystalline Si absorber. Recombination at the a‐Si:H/c‐Si‐interface is subsidiary in respect of the limitation of the open‐circuit voltage. Our best n‐type a‐Si:H/p‐type c‐Si solar cell prepared without high‐efficiency features such as back‐surface field or surface texturing has an independently confirmed efficiency of 14.1% and an open‐circuit voltage of 655 mV. Copyright © 2001 John Wiley & Sons, Ltd.     

Optimizing the diffused regions of interdigitated backside buried contact solar cells

Recombination and a number of other important factors must be considered in the optimization of the diffused regions of high‐efficiency silicon solar cells. In this paper, we examine issues related to the four types of diffusions used in rear‐junction, interdigitated backside buried contact solar cells made on n‐type silicon wafers: the phosphorus‐diffused front‐surface field (FSF), the boron‐diffused emitter, and the boron and the phosphorus diffused contact regions. Dark saturation current density, effective lifetime, implied open‐circuit voltage and sheet resistance are characterized for the optimization of the above‐mentioned diffused regions. Diffusion uniformity and the avoidance of the diffusion‐induced dislocations are also discussed for the heavily diffused, metal coated contact diffusions. It is found that the optimal sheet resistances of the FSF for planar and textured surfaces are 120 Ω/□ and 105 Ω/□ respectively, whereas the optimal post‐processing sheet resistance for the boron emitter is approximately 100 Ω/□. Moreover, sheet resistance as heavy as 10–20 Ω/□ for the boron groove diffusion and 5–10 Ω/□ for the phosphorus groove diffusion have been achieved without introducing the diffusion‐induced misfit dislocations. Careful consideration of the issues discussed here led to an absolute efficiency improvement on the planar n‐type IBBC solar cell of more than 0·6%. Copyright © 2006 John Wiley & Sons, Ltd.     

Optimizing annealing steps for crystalline silicon solar cells with screen printed front side metallization and an oxide‐passivated rear surface with local contacts

Silicon solar cells that feature screen printed front contacts and a passivated rear surface with local contacts allow higher efficiencies compared to present industrial solar cells that exhibit a full area rear side metallization. If thermal oxidation is used for the rear surface passivation, the final annealing step in the processing sequence is crucial. On the one hand, this post‐metallization annealing (PMA) step is required for decreasing the surface recombination velocity (SRV) at the aluminum‐coated oxide‐passivated rear surface. On the other hand, PMA can negatively affect the screen printed front side metallization leading to a lower fill factor. This work separately analyzes the impact of PMA on both, the screen printed front metallization and the oxide‐passivated rear surface. Measuring dark and illuminated IV‐curves of standard industrial aluminum back surface field (Al‐BSF) silicon solar cells reveals the impact of PMA on the front metallization, while measuring the effective minority carrier lifetime of symmetric lifetime samples provides information about the rear side SRV. One‐dimensional simulations are used for predicting the cell performance according to the contributions from both, the front metallization and the rear oxide‐passivation for different PMA temperatures and durations. The simulation also includes recombination at the local rear contacts. An optimized PMA process is presented according to the simulations and is experimentally verified. The optimized process is applied to silicon solar cells with a screen printed front side metallization and an oxide‐passivated rear surface. Efficiencies up to 18.1% are achieved on 148.8 cm² Czochralski (Cz) silicon wafers. Copyright © 2009 John Wiley & Sons, Ltd.     

Non‐Geminate Recombination as the Primary Determinant of Open‐Circuit Voltage in Polythiophene:Fullerene Blend Solar Cells: an Analysis of the Influence of Device Processing Conditions

The physical origin of the open‐circuit voltage in bulk heterojunction solar cells is still not well understood. While significant evidence exists to indicate that the open‐circuit voltage is limited by the molecular orbital energies of the heterojunction components, it is clear that this picture is not sufficient to explain the significant variations which often occur between cells fabricated from the same heterojunction components. We present here an analysis of the variation in open‐circuit voltage between 0.4–0.65 V observed for a range of P3HT/PCBM solar cells where device deposition conditions, electrode structure, active‐layer thickness and device polarity are varied. The analysis quantifies non‐geminate recombination losses of dissociated carriers in these cells, measured under device operating conditions. It is found that at open‐circuit, losses due to non‐geminate recombination are sufficiently large that other loss pathways may effectively be neglected. Variations in open‐circuit voltage between different devices are shown to arise from differences in the rate coefficient for non‐geminate recombination, and from differences in the charge densities in the photoactive layer of the device. The origin of these differences is discussed, particularly with regard to variations in film microstructure. By separately quantifying these differences in rate coefficient and charge density, and by application of a simple physical model based upon the assumption that open‐circuit is reached when the flux of charge photogeneration is matched by the flux of non‐geminate recombination, we are able to calculate correctly the open‐circuit voltage for all the cells studied to within an accuracy of ±5 mV.     

Enhanced Performance in Polymer Solar Cells by Surface Energy Control

Enhanced performance of an inverted‐type polymer solar cell is reported by controlling the surface energy of a zinc oxide (ZnO) buffer layer, on which a photoactive layer composed of a polymer:fullerene‐derivative bulk heterojunction is formed. With the approach based on a mixed self‐assembled monolayer, the surface energy of the ZnO buffer layer can be controlled between 40 mN m^?1 and 70 mN m^?1 with negligible changes in its work function. For the given range of surface energy the power conversion efficiency increases from 3.27% to 3.70% through enhanced photocurrents. The optimized morphology obtained by surface energy control results in the enhanced photocurrent and transmission electron microscopy analysis verifies the correlation between the surface energy and the phase morphology of the bulk heterojunction. These results demonstrate that surface energy control is an effective method for further improving the performance of polymer solar cells, with potentially important implications for other organic devices containing an interface between a blended organic active layer and a buffer or an electrode layer.     

Impact of spatial separation of type‐II GaSb quantum dots from the depletion region on the conversion efficiency limit of GaAs solar cells

The purpose of this work is to look for a practical structure for application of quantum dots (QDs) in solar cells. We focus on a stack of strain‐compensated GaSb/GaAs type‐II QDs. We propose a novel structure with GaSb/GaAs type‐II QD absorber embedded in the p‐doped region of ideal solar cell but spatially separated from the depletion region. We developed the model and used the detailed balance principle along with Poisson and continuity equations for calculating of the energy band bending and photovoltaic characteristics of the proposed solar cell. Our model takes into account both single‐photon and two‐photon absorption as well as non‐radiative processes in QDs and predicts that concentration from 1‐sun to 500‐sun increases the efficiency from 30% to 50%. We showed that accumulation of charge in the QD absorber is the clue to understanding of potentially superior performance of the proposed solar cell. An attractive feature of the proposed solar cell is that QDs do not reduce the open‐circuit voltage but facilitate generation of the additional photocurrent to the extent that photovoltaic characteristics reduce to that of ideal solar cell while the efficiency meets the Luque‐Marti limit. It should be noted that although non‐radiative processes like relaxation in QDs and recombination through QDs degrade photovoltaic characteristics of the proposed solar cell, its conversion efficiency is still predicted to be above the Shockley‐Queisser limit by 5% to 10%. This study is an important step toward producing practical solar cells that benefit from additional photocurrent generated by sub‐band gap photons. Copyright © 2014 John Wiley & Sons, Ltd.     

Belt furnace gettering and passivation of n‐web silicon for high‐efficiency screen‐printed front‐surface‐field solar cells

Six different resistivities (0.32, 0.57, 1.2, 2.2, 9.1 and 20 Ω cm) were investigated to understand the dopant–defect interaction in n‐type, antimony‐doped, dendritic web silicon ribbon, and to study its response to gettering and passivation during belt furnace processing (BFP). The as‐grown lifetime was found to be a strong function of resistivity with higher resistivity displaying higher lifetime. Phosphorus gettering at 925° C/6 min raised the as‐grown lifetime of ∼1 μs in 20 Ω cm n‐web to 5.4 μs. A combination of phosphorus gettering followed by simultaneous Al gettering and SiN hydrogenation raised the 20 Ω cm n‐web lifetime to 78 μs. Unlike the as‐grown web, the processed lifetime was greater than 75 μs for all resistivities, with no clear doping dependence. This is attributed to the very effective gettering and passivation during the belt furnace processing. Front surface field (FSF) n⁺–n–p⁺ cells were fabricated by spin‐on phosphorus diffusion on the front and screen‐printed Al on the back. A lifetime value of over 100 μs was obtained in a 14.2% screen‐printed FSF n‐web solar cell fabricated on 100‐μm‐thick 20 Ω cm substrate. The screen‐printed FSF cell fabricated on (111) FZ gave an efficiency of 14.9% with a fill factor of 77.6%. These results are supported by model calculations, which revealed a maximum efficiency of ∼15% for 100‐μm‐thick planar screen‐printed FSF cells and their insensitivity to bulk lifetime above 60 μs. Copyright © 2001 John Wiley & Sons, Ltd.     

A Simple Way to Simultaneously Release the Interface Stress and Realize the Inner Encapsulation for Highly Efficient and Stable Perovskite Solar Cells

The mixed halide perovskites have become famous for their outstanding photoelectric conversion efficiency among new‐generation solar cells. Unfortunately, for perovskites, little effort is focused on stress engineering, which should be emphasized for highly efficient solar cells like GaAs. Herein, polystyrene (PS) is introduced into the perovskite solar cells as the buffer layer between the SnO₂ and perovskite, which can release the residual stress in the perovskite during annealing because of its low glass transition temperature. The stress‐free perovskite has less recombination, larger lattices, and a lower ion migration tendency, which significantly improves the cell's efficiency and device stability. Furthermore, the so‐called inner‐encapsulated perovskite solar cells are fabricated with another PS capping layer on the top of perovskite. As high as a 21.89% photoelectric conversion efficiency (PCE) with a steady‐state PCE of 21.5% is achieved, suggesting that the stress‐free cell can retain almost 97% of its initial efficiency after 5 days of “day cycle” stability testing.     

Surface recombination velocity in MINP solar cells

Proper passivation of the front surface of the homojunction solar cell is an essential ingredient of the recent efforts to achieve the theoretical efficiency predicted for silicon solar cells. In this paper, we derive an expression for the surface recombination velocity, C_p, of the MINP solar cell. We take into account the surface states and the tunnel probability across the thin passivation SiO₂ layer on top of the Si surface. The implication of this expression to the proper design of the MINP solar cell is discussed.     

DC‐sputtered ZnO:Al as transparent conductive oxide for silicon heterojunction solar cells with µc‐Si:H emitter

Silicon heterojunction (SHJ) solar cells are highly interesting, because of their high efficiency and low cost fabrication. So far, the most applied transparent conductive oxide (TCO) is indium tin oxide (ITO). The replacement of ITO with cheaper, more abundant and environmental friendly material with texturing capability is a promising way to reduce the production cost of the future SHJ solar cells. Here, we report on the fabrication of the SHJ solar cells with direct current‐sputtered aluminum‐doped zinc oxide (ZnO:Al) as an alternative TCO. Furthermore, we address several important differences between ITO and the ZnO:Al layers including a high Schottky barrier at the emitter/ZnO:Al interface and a high intrinsic resistivity of the ZnO:Al layers. To overcome the high Schottky barrier, we suggest employing micro‐crystalline silicon (µc‐Si:H) emitter, which also improves temperature threshold and passivation of the solar cell precursor. In addition, we report on the extensive studies of the effect of the ZnO:Al deposition parameters including layer thickness, oxygen flow, power density and temperature on the electrical properties of the fabricated SHJ solar cells. Finally, the results of our study indicate that the ZnO:Al deposition parameters significantly affect the electrical properties of the obtained solar cell. By understanding and fine‐tuning all these parameters, a high conversion efficiency of 19.2% on flat wafer (small area (5 × 5 mm²) and without any front metal grid) is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Cu2ZnSnSe4 thin film solar cells produced via co‐evaporation and annealing including a SnSe2 capping layer

Cu₂ZnSnSe₄ (CZTSe) thin film solar cells have been produced via co‐evaporation followed by a high‐temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe₂ capping layer has been evaporated onto the absorber prior to the high‐temperature treatment. This eliminates the Sn losses due to SnSe evaporation. A solar cell efficiency of 5.1% could be achieved with this method. Moreover, the device does not suffer from high series resistance, and the dominant recombination pathway is situated in the absorber bulk. Finally, different illumination conditions (white light, red light, and yellow light) reveal a strong loss in fill factor if no carriers are generated in the CdS buffer layer. This effect, known as red‐kink effect, has also been observed in the closely related Cu(In,Ga)Se₂ thin film solar cells. Copyright © 2013 John Wiley & Sons, Ltd.