Cu2FeSnS4-based heterojunction solar cells with MxOy (M=Cu, Ni)-back surface field layers: Impact of defect density states and recombination

Copper-based chalcogenide quaternary semiconductors have emerged as promising candidates for next-generation photovoltaic (PV) devices, owing to their unique electronic and photonic properties coupled with environmentally friendly compositions. This study explores the potential of copper-based absorber materials, specifically Cu₂FeSnS₄ (CFTS), as an absorber in heterojunction solar cells with Cu-/Ni-metal oxides back surface field (BSF) and SnS₂ buffer layers using the SCAPS-1D Simulator. Initially, we assess the performance of CFTS-absorber solar cells and compare the key photovoltaic metrics with those of other Cu-based semiconductors including CuIn_xGa_(1-x)Se₂ (CIGS), Cu₂ZnSnS₄ (CZTS), Cu₂CoSnS₄ (CCTS), Cu₂NiSnS₄ (CNTS), Cu₂BaSnS₄ (CBTS), Cu₂MnSnS₄ (CMTS), to identify the most promising absorber. Subsequently, we optimize the layer properties, including active layer thickness, free-carrier concentration, bulk and interface defect density, and carrier recombination in potential CFTS. Further, we examine the impact of defects, and carrier recombination, including radiative, Shockley-Read-Hall (SRH), and Auger recombination. These detailed studies yield improved and competitive photoconversion efficiency, (PCE) of 27.31% (compared to 24.68%, without BSF) with open circuit voltage, (V_OC) of 1.36 V, short-circuit current density, (J_SC) of 22.28 mA/cm² and fill factor, (FF) of 90.47% for Cu₂O, whereas the PCE of 26.97% with V_OC of 1.07 V, J_SC of 28.82 mA/cm² and FF of 86.91% for NiO_x BSF layer in Au/Mo/BSF(Cu₂O and NiO_x)/CFTS/SnS₂/ZnMgO/ZnO:Al/Pt configurations under optimized conditions. The enhanced charge separation and carrier collection efficiencies reveal the strong potential of CFTS absorber heterostructures with Cu₂O/NiO_x, SnS_2, and bi-layer ZnMgO/ZnO:Al as BSF, buffer, and window layers, repectively, providing insights and resources for developing high-efficiency CFTS-based photovoltaic devices.