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The SnZn defect passivation and heterojunction interface energetics‐modification are crucial for further improvement of open‐circuit voltage (Voc) and efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, a simple but effective cation substitution strategy is reported to promote the performance of CZTSSe devices by simultaneously modifying the absorber and heterojunction interface. This is achieved by introducing the organic silicon salt C8H20O4Si into CZTSSe precursor solution as a source of silicon to partially substitute Sn with Si. Systematic studies reveal that there are two mechanisms synergistically contributing to the increase of efficiency: 1) This strategy can passivate the undesired SnZn defect in CZTSSe absorber more efficiently, leading to at least one order of magnitude lower SnZn defect density and beneficial carrier transport properties; 2) After Si incorporation, the conduction band minimum of the CZTSSe is upshifted, thus enlarging the bandgap, which ultimately optimizes the energy level structure at the CdS/CZTSSe interface and reduces interfacial energy loss by decreasing the carrier transport barrier. Consequently, the CZTSSe device with 7% Si substitution delivers a satisfactory efficiency of 13.02% owing to an increase in Voc. It is hoped the Si substitution strategy reported here can provide inspiration for developing advanced CZTSSe devices with broad application prospects. [ABSTRACT FROM AUTHOR]

The photovoltaic performance of the environmentally friendly Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is lower than its predecessor Cu(In,Ga)Se2 solar cells. Severe carrier recombination at the CZTSSe/CdS interface is one major reason that results in a large open‐circuit voltage loss. Doping zinc into CdS is a feasible strategy to modifying the CdS buffer layer film, but the present methods are not satisfactory. In this study, novel zinc incorporation strategy is developed to deposit a gradient composition ternary ZnxCd1–xS buffer layer for optimizing the heterojunction interface. The application of gradient composition ZnxCd1–xS buffer layer constructs a gradient conduction band energy configuration in the CZTSSe/buffer layer interface, which highly reduces the interface recombination. The suppressed interface recombination contributes to the enhanced open circuit voltage and device performance. Consequently, the CZTSSe solar cell based on gradient composition ZnxCd1–xS buffer layers achieves champion efficiency of 12.35% with VOC of 504.81 mV, JSC of 36.90 mA cm−2, and FF of 66.28%. It is worth noting that flammable and the toxic hydrazine solvent are replaced by the safe and low‐toxic 2‐methoxyethanol, making it more promising for the future commercialization of CZTSSe solar cells. [ABSTRACT FROM AUTHOR]

The doping of indium into absorber layer has been proven to be beneficial for hybrid buffer structured Cu 2 ZnSn(S, Se) 4 (CZTSSe) solar cells, but it is difficult to precisely control the doping content only relying on In diffusion from In 2 S 3 emitter. Herein, we use the solution method to prepare In-substituted CZTSSe layer by directly doping In 2 Se 3 into metal chalcogenides precursor solution. The doping content can be precisely controlled and the influences of indium doping on cell performance are systematically discussed. Mott-Schottky and resistivity measurements indicate that the carrier concentration and charge transport process are monotonically enhanced with increasing In/(In + Sn) content (0 at.%, 3 at.%, 6 at.% and 12 at.%). The improvements of series resistance also lead to a monotonic increase of fill factor ( FF ) from 52.1% to 64.8%. Due to the larger recombination at high doping content, the 6 at.% In content device finally contributes the highest power conversion efficiency of 8.47%. It is expected that a precisely controlled indium doping could further improve cell performance for efficient hybrid buffer structured devices. [ABSTRACT FROM AUTHOR]