Analysis of the Improvement of Photoelectrical Properties of Cu2ZnSn(S,Se)4 Thin Film and Solar Cells Via Cation Doping

Solar energy has been recognized as an alternative energy source that can help address fuel depletion and climate change issues. As a renewable energy alternative to fossil fuels, it is an eco-friendly and unlimited energy source. Among solar cells, thin film Cu2ZnSn(S,Se)(4) (CZTSSe) is currently being actively studied as an alternative to heavily commercialized Cu (In,Ga)Se-2 (CIGS) thin film solar cells, which rely upon costly and scarce indium and gallium. Currently, the highest efficiency achieved by CZTSSe cells is 14.9 %, lower than the CIGS record of 23.35 %. When applied to devices, CZTSSe thin films perform poorly compared to other materials due to problems including lattice defects, conduction band offset, secondary phase information, and narrow stable phase regions, so improving their performance is essential. Research into ways of improving performance by doping with Germanium and Cadmium is underway. Specifically, Ge can be doped into CZTSSe, replacing Sn to reduce pinholes and bulk recombination. Additionally, partially replacing Zn with Cd can facilitate grain growth and suppress secondary phase formation. In this study, we analyzed the device's performance after doping Ge into CZTSSe thin film using evaporation, and doping Cd using chemical bath deposition. The Ge doped thin film showed a larger bandgap than the undoped reference thin film, achieving the highest V(oc )of 494 mV in the device. The Cd doped thin film showed a smaller band- gap than the undoped reference thin film, with the highest J(sc)of 36.9 mA/cm(2). As a result, the thin film solar cells achieved a power conversion efficiency of 10.84 %, representing a 20 % improvement in power conversion efficiency compared to the undoped reference device.