Computational Study of Performance Dependence of SnO2: F/i-SnO2 /CdS /Cu2ZnSn (SxSe1–x)4 Solar Cell on S/Se Molar Composition

Characteristics of high efficiency, heterojunction solar cell with Cu2ZnSn(SxSe1–x)4 (CZTSSe) absorber layer, CdS buffer layer, and bilayers of SnO2:F (FTO) and undoped SnO2 Transparent Conducting Oxides (TCOs) was comprehensively investigated by numerical simulation. Notably, the kesterite structure of CZTSSe offers advantages such as an ideal direct bandgap (1–1.5 eV), high absorption coefficient, and earth-abundant constituent materials, making it an environmentally friendly alternative to traditional photovoltaic materials. The cell performance was explored by varying sulphur and selenium molar fractions in the absorber layer, providing insights into the effects of molar composition on device efficiency. The composition-dependent optimization demonstrated that efficiency initially increases with sulphur content, reaching a maximum before declining. Maximum efficiency of 21.09% is achieved when Cu2ZnSn(S0.6Se0.4)4 absorber layer is used. A maximum efficiency of 21.35% was achieved when Cu2ZnSn(S0.8Se0.2)4 absorber layer with textured front surface with an angle of 54.74°is used, which significantly enhances the light absorption capability. Variation of solar cell irradiation revealed that the electrical performance parameters of the cell increase with light intensity. Maximum open circuit voltage was 981 mV for Cu2ZnSnS4, and maximum short-circuit current was found to be 91.02 mA/cm² for Cu2ZnSnSe4 with textured front surface under 2000 W/m² irradiation. Variations in absorber layer thickness were also analyzed. The saturated open circuit voltage for Cu2ZnSn(S0.6Se0.4)4 is 789.6 mV with plane front and the optimum thickness is 2.87 µm and for Cu2ZnSn(S0.8Se0.2)4 saturated open circuit voltage is 881.1 mV with textured front with optimum thickness 4.2 µm. The short circuit current density saturation occurs at 36.4 mA/cm2 with 15 µm and 32.3 mA/cm2 with 15 µm for and Cu2ZnSn(S0.6Se0.4)4 and Cu2ZnSn(S0.8Se0.2)4, respectively. Efficiency saturates at 24.4 % for Cu2ZnSn(S0.8Se0.2)4 and at 23.5% for Cu2ZnSn(S0.6Se0.4)4 for 15 µm. These findings suggest that CZTSSe-based solar cells are a promising solution for sustainable, high-efficiency photovoltaic technology.