为了降低电子传输层(Electron transport layer,ETL)与钙钛矿层之间的界面缺陷态密度,通过旋涂法在氧化铟锡(Indium tin oxide,ITO)透明导电玻璃上制备一层SnO_(2)电子传输层,并在其上表面旋涂(NH_(4))_(2)S以修饰SnO_(2)和钙钛矿光吸...为了降低电子传输层(Electron transport layer,ETL)与钙钛矿层之间的界面缺陷态密度,通过旋涂法在氧化铟锡(Indium tin oxide,ITO)透明导电玻璃上制备一层SnO_(2)电子传输层,并在其上表面旋涂(NH_(4))_(2)S以修饰SnO_(2)和钙钛矿光吸收层之间的界面。通过X射线光电子能谱、扫描电子显微镜、电化学阻抗谱等表征手段分析(NH_(4))_(2)S修饰对钙钛矿太阳能电池(Perovskite solar cells,PSCs)光电性能的影响。结果表明:NH_(4)^(+)降低了SnO_(2)的表面羟基(—OH)缺陷态密度,增强了界面的疏水性,减少了钙钛矿的形核位点,增大了钙钛矿晶粒;S^(2-)填补了SnO_(2)表面的氧空位(OV),同时部分S^(2-)还与未配位Pb^(2+)连接减少界面处Pb缺陷,抑制了界面处载流子复合;经过(NH_(4))_(2)S的修饰,PSCs开路电压从1.07 V提高到1.11 V,光电转化效率达到了20.53%。(NH_(4))2S修饰后的PSCs具有更高的光电转化效率、更好的长期稳定性。该研究可为PSCs商业化提供新的思路。展开更多
The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large ...The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit(V_(oc,deficit)) and significantly limit kesterite photovoltaics performance,primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered Cu_(Zn) defects and generate benign n-type Zn_(Ag) donors. Taking advantage of the decreased annealing temperature of Ag F post deposition treatment(PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the Ag F-PDT device finally achieves maximum efficiency of 12.34% with enhanced V_(oc) of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.展开更多
It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple soluti...It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple solution method,and then the effects on the surface properties of the absorber layer,the buffer layer growth,and the modifications of the solar cell performance induced by the Na doping are studied.The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping.In addition,the contact angle of the surface increases because of Na doping.As a consequence,the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased.The difference of quasi-Fermi levels(EFn-EFp) increases with a small amount of Na doping in the CZTSSe solar cell,so that open circuit voltage(VOC) increased significantly.This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.展开更多
Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handl...Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handling spin-coating method, a thin PCBM([6,6]-phenyl-C61-butyric acid methyl ester) layer as an electron extraction layer has been introduced on the top of CdS buffer layer to modify CZTSSe/CdS/ZnO-ITO(In_(2)O_(3):Sn) interfacial properties. Based on Sn^(4+)/DMSO(dimethyl sulfoxide) solution system, a totalarea efficiency of 12.87% with a VOC of 529 m V has been achieved. A comprehensive investigation on the influence of PCBM layer on carrier extraction, transportation and recombination processes has been carried out. It is found that the PCBM layer can smooth over the Cd S film roughness, thus beneficial for a dense and flat window layer. Furthermore, this CZTSSe/Cd S/PCBM heterostructure can accelerate carrier separation and extraction and block holes from the front interface as well, which is mainly ascribed to the downward band bending of the absorber and a widened space charge region. Our work provides a feasible way to improve the front interfacial property and the cell performance of CZTSSe solar cells by the aid of organic interfacial materials.展开更多
Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface...Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface and passivate deep level defects in CZTSSe bulk concurrently for improving the performance of flexible device.The results show that In doping effectively inhibits the formation of secondary phase(Cu(S,Se)_(2))and VSndefects.Further studies demonstrate that the barrier height at the back interface is decreased and the deep level defects(Cu_(Sn)defects)in CZTSSe bulk are passivated.Moreover,the carrier concentration is increased and the V_(OC) deficit(V_(OC,def))is decreased significantly due to In doping.Finally,the flexible CZTSSe solar cell with 10.01%power conversion efficiency(PCE)has been obtained.The synergistic strategy of interface modification and bulk defects passivation through In incorporation provides a new thought for the fabrication of efficient flexible kesterite-based solar cells.展开更多
Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)has attracted considerable attention as a non-toxic and earthabundant solar cell material.During selenization of CZTSSe film at high temperature,the reaction between CZTSSe and Mo...Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)has attracted considerable attention as a non-toxic and earthabundant solar cell material.During selenization of CZTSSe film at high temperature,the reaction between CZTSSe and Mo is one of the main reasons that result in unfavorable absorber and interface quality,which leads to large open circuit voltage deficit(VOC-def)and low fill factor(FF).Herein,a WO_(3)intermediate layer introduced at the back interface can effectually inhibit the unfavorable interface reaction between absorber and back electrode in the preliminary selenization progress;thus high-quality crystals are obtained.Through this back interface engineering,the traditional problems of phase segregation,voids in the absorber and over thick Mo(S,Se)_(2)at the back interface can be well solved,which greatly lessens the recombination in the bulk and at the interface.The increased minority carrier diffusion length,decreased barrier height at back interface contact and reduced deep acceptor defects give rise to systematic improvement in VOCand FF,finally a 12.66%conversion efficiency for CZTSSe solar cell has been achieved.This work provides a simple way to fabricate highly efficient solar cells and promotes a deeper understanding of the function of intermediate layer at back interface in kesterite-based solar cells.展开更多
The use of transparent conducting oxide(TCO)as a substrate in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin-film solar cells allows for advanced applications,such as bifacial,semitransparent,and tandem solar cells with the capabil...The use of transparent conducting oxide(TCO)as a substrate in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin-film solar cells allows for advanced applications,such as bifacial,semitransparent,and tandem solar cells with the capability to increase power density generation.However,the efficiency of this kind of solar cell is still below 6% based on the low-cost solution process.In this work,we develop a composition gradient strategy and demonstrate a 6.82% efficient CZTSSe solar cell on F:SnO_(2)(FTO)substrate under the ambient condition.The composition gradient is realized by simply depositing the precursor inks with different Zn/Sn ratios.To verify that the high performance of the solar cell is attributed to the composition gradient strategy rather than the sole change of the Zn/Sn ratio,devices based on absorbers with varied Zn/Sn ratios are fabricated.Furthermore,the structure and surface morphology of the CZTSSe films with/without composition gradients are examined.The presence of elemental gradient through the depth of the CZTSSe films before and after annealing is confirmed by secondary ion mass spectroscopy analysis.It is found that the composition gradient enhances the crystallinity of the absorber,reduces the surface roughness as well as device parasitic losses,contributing to a higher fill factor,open-circuit voltage,and conversion efficiency.展开更多
Hydrothermal deposition of antimony selenosulfide(Sb_(2)(S,Se_(3)))has enabled solar cell applications to surpass the 10%efficiency threshold.This deposition process involves the reaction of three precursor materials:...Hydrothermal deposition of antimony selenosulfide(Sb_(2)(S,Se_(3)))has enabled solar cell applications to surpass the 10%efficiency threshold.This deposition process involves the reaction of three precursor materials:Sb,S,and Se.However,this process generates an unfavourable gradient of Se and S anions in the Sb_(2)(S,Se)_(3)film,which limits further efficiency improvements.Herein,we demonstrate how NH_(4)F can be used as an additive to regulate the band gradient of the Sb_(2)(S,Se)_(3)and modify the surface of the CdS electron-transporting layer.On the one hand,NH_(4)F inhibits the decomposition of Na_(2)S_(2)O_(3)and selenourea,which optimizes the deposition process and allows for adjustment of the Se/S ratio and their distribution in the Sb_(2)(S,Se)_(3)film.On the other hand,hydrolysis of NH_(4)F induces dissolution and redeposition of CdS,thereby effectively improving the morphology and crystallinity of the CdS substrate.Finally,the dual effect of NH_(4)F enables improved surface morphology and energy alignment of the Sb_(2)(S,Se)_(3)film,thus yielding a maximum efficiency of 10.28%,a 12%improvement over the control device.This study demonstrates an effective strategy for simultaneously modifying a sulfide-based substrate and regulating the element distribution during the deposition of a metal chalcogenide film for optoelectronic device applications.展开更多
Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin film solar cells have been regarded as one of the most promising thin film photovoltaic technologies,offering a low-cost and environmentally friendly solar energy option.Alth...Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin film solar cells have been regarded as one of the most promising thin film photovoltaic technologies,offering a low-cost and environmentally friendly solar energy option.Although remarkable advances have been achieved in kesterite solar cells,the performance gap relative to mature thin film photovoltaic technologies such as CIGSe and Cd Te remains large.Significant open-circuit voltage(V_(OC))deficit has been recognized as the main limiting factor to performance improvement,with undesirable intrinsic defects being a key culprit contributing to the low V_(OC).To realize the promise inherent in kesterite CZTS to become an earth-abundant alternative to existing thin film photovoltaic technologies with comparable performance,significant research effort has been invested to tackle the challenging defect issues.In this review,recent progress and achievements relevant to engineering improvements to the defect properties of the semiconductor have been examined and summarized.Promising strategies include:(i)manipulating the synthesis process to obtain a desirable reaction pathway and chemical environment;(ii)introducing cation substitution to increase the ionic size difference and supress the related band tailing deep-level defects;(iii)applying post deposition treatment(PDT)with alkaline elements to passivate the detrimental defects.These advances obtained from work on kesterite solar cells may lead to future high performance from this material and may be further extended to other earth-abundant chalcogenide photovoltaic technologies.展开更多
文摘为了降低电子传输层(Electron transport layer,ETL)与钙钛矿层之间的界面缺陷态密度,通过旋涂法在氧化铟锡(Indium tin oxide,ITO)透明导电玻璃上制备一层SnO_(2)电子传输层,并在其上表面旋涂(NH_(4))_(2)S以修饰SnO_(2)和钙钛矿光吸收层之间的界面。通过X射线光电子能谱、扫描电子显微镜、电化学阻抗谱等表征手段分析(NH_(4))_(2)S修饰对钙钛矿太阳能电池(Perovskite solar cells,PSCs)光电性能的影响。结果表明:NH_(4)^(+)降低了SnO_(2)的表面羟基(—OH)缺陷态密度,增强了界面的疏水性,减少了钙钛矿的形核位点,增大了钙钛矿晶粒;S^(2-)填补了SnO_(2)表面的氧空位(OV),同时部分S^(2-)还与未配位Pb^(2+)连接减少界面处Pb缺陷,抑制了界面处载流子复合;经过(NH_(4))_(2)S的修饰,PSCs开路电压从1.07 V提高到1.11 V,光电转化效率达到了20.53%。(NH_(4))2S修饰后的PSCs具有更高的光电转化效率、更好的长期稳定性。该研究可为PSCs商业化提供新的思路。
基金supported by the National Natural Science Foundation of China(61874159,62074052,61974173,52072327,51702085 and 51802081)the Joint Talent Cultivation Funds of NSFC-HN(U1704151 and U1904192)+1 种基金the Zhongyuan Thousand Talents(Zhongyuan Scholars)Program of Henan Province(202101510004)the Science and Technology Innovation Talents in Universities of Henan Province(21HASTIT023)。
文摘The environmentally friendly Cu_(2)ZnSn(S,Se)_(4)(CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit(V_(oc,deficit)) and significantly limit kesterite photovoltaics performance,primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered Cu_(Zn) defects and generate benign n-type Zn_(Ag) donors. Taking advantage of the decreased annealing temperature of Ag F post deposition treatment(PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the Ag F-PDT device finally achieves maximum efficiency of 12.34% with enhanced V_(oc) of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.
基金supported by the National Key R&D Program of China(2019YFB1503500,2018YFB1500200,2018YEE0203400)the Natural Science Foundation of China(U1902218,11774187)the 111 project(B16027)。
文摘It is very important to understand why a small amount of alkali metal doping in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells can improve the conversion efficiency.In this work,Na-doped CZTSSe is prepared by a simple solution method,and then the effects on the surface properties of the absorber layer,the buffer layer growth,and the modifications of the solar cell performance induced by the Na doping are studied.The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping.In addition,the contact angle of the surface increases because of Na doping.As a consequence,the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased.The difference of quasi-Fermi levels(EFn-EFp) increases with a small amount of Na doping in the CZTSSe solar cell,so that open circuit voltage(VOC) increased significantly.This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.
基金supported by the National Natural Science Foundation of China(U2002216,52172261,51627803,51972332,22075150,and U1902218)the National Key Research and Development Program of China(2019YFE0118100)。
文摘Photo-generated carrier recombination loss at the CZTSSe/Cd S front interface is a key issue to the opencircuit voltage(V_(OC)) deficit of Cu_(2)ZnSnS_(x)Se_(4-x)(CZTSSe) solar cells. Here, by the aid of an easy-handling spin-coating method, a thin PCBM([6,6]-phenyl-C61-butyric acid methyl ester) layer as an electron extraction layer has been introduced on the top of CdS buffer layer to modify CZTSSe/CdS/ZnO-ITO(In_(2)O_(3):Sn) interfacial properties. Based on Sn^(4+)/DMSO(dimethyl sulfoxide) solution system, a totalarea efficiency of 12.87% with a VOC of 529 m V has been achieved. A comprehensive investigation on the influence of PCBM layer on carrier extraction, transportation and recombination processes has been carried out. It is found that the PCBM layer can smooth over the Cd S film roughness, thus beneficial for a dense and flat window layer. Furthermore, this CZTSSe/Cd S/PCBM heterostructure can accelerate carrier separation and extraction and block holes from the front interface as well, which is mainly ascribed to the downward band bending of the absorber and a widened space charge region. Our work provides a feasible way to improve the front interfacial property and the cell performance of CZTSSe solar cells by the aid of organic interfacial materials.
基金supported by the National Natural Science Foundation of China(62074037)the Science and Technology Department of Fujian Province(2020I0006)the Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(2021ZZ124)。
文摘Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface and passivate deep level defects in CZTSSe bulk concurrently for improving the performance of flexible device.The results show that In doping effectively inhibits the formation of secondary phase(Cu(S,Se)_(2))and VSndefects.Further studies demonstrate that the barrier height at the back interface is decreased and the deep level defects(Cu_(Sn)defects)in CZTSSe bulk are passivated.Moreover,the carrier concentration is increased and the V_(OC) deficit(V_(OC,def))is decreased significantly due to In doping.Finally,the flexible CZTSSe solar cell with 10.01%power conversion efficiency(PCE)has been obtained.The synergistic strategy of interface modification and bulk defects passivation through In incorporation provides a new thought for the fabrication of efficient flexible kesterite-based solar cells.
基金supported by the National Key R&D Program of China(no.2018YFE0203400)the National Natural Science Foundation of China(no.62074102)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(no.2022A1515010979)the Science and Technology plan project of Shenzhen(nos.JCYJ20190808120001755 and 20220808165025003)。
文摘Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)has attracted considerable attention as a non-toxic and earthabundant solar cell material.During selenization of CZTSSe film at high temperature,the reaction between CZTSSe and Mo is one of the main reasons that result in unfavorable absorber and interface quality,which leads to large open circuit voltage deficit(VOC-def)and low fill factor(FF).Herein,a WO_(3)intermediate layer introduced at the back interface can effectually inhibit the unfavorable interface reaction between absorber and back electrode in the preliminary selenization progress;thus high-quality crystals are obtained.Through this back interface engineering,the traditional problems of phase segregation,voids in the absorber and over thick Mo(S,Se)_(2)at the back interface can be well solved,which greatly lessens the recombination in the bulk and at the interface.The increased minority carrier diffusion length,decreased barrier height at back interface contact and reduced deep acceptor defects give rise to systematic improvement in VOCand FF,finally a 12.66%conversion efficiency for CZTSSe solar cell has been achieved.This work provides a simple way to fabricate highly efficient solar cells and promotes a deeper understanding of the function of intermediate layer at back interface in kesterite-based solar cells.
基金supported by the National Natural Science Foundation of China(62074168)the Fundamental Research Foundations for the Central Universities(20lgpy04)。
文摘The use of transparent conducting oxide(TCO)as a substrate in Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin-film solar cells allows for advanced applications,such as bifacial,semitransparent,and tandem solar cells with the capability to increase power density generation.However,the efficiency of this kind of solar cell is still below 6% based on the low-cost solution process.In this work,we develop a composition gradient strategy and demonstrate a 6.82% efficient CZTSSe solar cell on F:SnO_(2)(FTO)substrate under the ambient condition.The composition gradient is realized by simply depositing the precursor inks with different Zn/Sn ratios.To verify that the high performance of the solar cell is attributed to the composition gradient strategy rather than the sole change of the Zn/Sn ratio,devices based on absorbers with varied Zn/Sn ratios are fabricated.Furthermore,the structure and surface morphology of the CZTSSe films with/without composition gradients are examined.The presence of elemental gradient through the depth of the CZTSSe films before and after annealing is confirmed by secondary ion mass spectroscopy analysis.It is found that the composition gradient enhances the crystallinity of the absorber,reduces the surface roughness as well as device parasitic losses,contributing to a higher fill factor,open-circuit voltage,and conversion efficiency.
基金the National Natural Science Foundation of China(22005293 and U19A2092)the National Key Research and Development Program of China(2019YFA0405600).
文摘Hydrothermal deposition of antimony selenosulfide(Sb_(2)(S,Se_(3)))has enabled solar cell applications to surpass the 10%efficiency threshold.This deposition process involves the reaction of three precursor materials:Sb,S,and Se.However,this process generates an unfavourable gradient of Se and S anions in the Sb_(2)(S,Se)_(3)film,which limits further efficiency improvements.Herein,we demonstrate how NH_(4)F can be used as an additive to regulate the band gradient of the Sb_(2)(S,Se)_(3)and modify the surface of the CdS electron-transporting layer.On the one hand,NH_(4)F inhibits the decomposition of Na_(2)S_(2)O_(3)and selenourea,which optimizes the deposition process and allows for adjustment of the Se/S ratio and their distribution in the Sb_(2)(S,Se)_(3)film.On the other hand,hydrolysis of NH_(4)F induces dissolution and redeposition of CdS,thereby effectively improving the morphology and crystallinity of the CdS substrate.Finally,the dual effect of NH_(4)F enables improved surface morphology and energy alignment of the Sb_(2)(S,Se)_(3)film,thus yielding a maximum efficiency of 10.28%,a 12%improvement over the control device.This study demonstrates an effective strategy for simultaneously modifying a sulfide-based substrate and regulating the element distribution during the deposition of a metal chalcogenide film for optoelectronic device applications.
基金supported by the Australian Renewable Energy Agency(Grant Nos.1-USO028,and 2017/RND006)the Australian Research Council(ARC)Future Fellowship Programme(Grant No.FT190100756)the ACAP Postdoctoral Fellowship Supported by Australian Centre for Advanced Photovoltaics(Grant No.1-SRI001)。
文摘Kesterite Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)thin film solar cells have been regarded as one of the most promising thin film photovoltaic technologies,offering a low-cost and environmentally friendly solar energy option.Although remarkable advances have been achieved in kesterite solar cells,the performance gap relative to mature thin film photovoltaic technologies such as CIGSe and Cd Te remains large.Significant open-circuit voltage(V_(OC))deficit has been recognized as the main limiting factor to performance improvement,with undesirable intrinsic defects being a key culprit contributing to the low V_(OC).To realize the promise inherent in kesterite CZTS to become an earth-abundant alternative to existing thin film photovoltaic technologies with comparable performance,significant research effort has been invested to tackle the challenging defect issues.In this review,recent progress and achievements relevant to engineering improvements to the defect properties of the semiconductor have been examined and summarized.Promising strategies include:(i)manipulating the synthesis process to obtain a desirable reaction pathway and chemical environment;(ii)introducing cation substitution to increase the ionic size difference and supress the related band tailing deep-level defects;(iii)applying post deposition treatment(PDT)with alkaline elements to passivate the detrimental defects.These advances obtained from work on kesterite solar cells may lead to future high performance from this material and may be further extended to other earth-abundant chalcogenide photovoltaic technologies.
