Performance evaluation of ZnSnN₂ solar cells with Si back surface field using SCAPS-1D: A theoretical study

The earth-abundant semiconductor zinc tin nitride (ZnSnN₂) has garnered significant attention as a prospective material in photovoltaic and lighting applications, primarily due to its tunable narrow bandgap and high absorption coefficient. This study focuses on a numerical investigation of ZnSnN₂ solar cell structures using the SCAPS 1-D software. The objective is to analyze the influence of various physical and geometrical parameters on solar cell performance. These parameters include the thicknesses of the ZnO window layer, CdS buffer layer, ZnSnN₂ absorber layer, and Si back surface field layer (BSF), as well as operating temperature, series and shunt resistances (R_S and R_sh), absorber layer defect density, interface defects, and the generation-recombination profile of the n-ZnO:Al/n-CdS/p-ZnSnN₂/p-Si/Mo structure. We have evaluated the capabilities of this novel material absorber by investigating its performance across a range of thicknesses. We have started with ultrathin absorber thicknesses and gradually increased them to thicker levels to determine the optimal thickness for achieving high efficiency. Under optimal conditions, a thin solar cell with a thickness (w_p) of 1 μm achieved an efficiency (η) of 23.9%. In a practical solar cell operating at room temperature, optimal parameters were observed with a thicker absorber layer (w_p = 8 μm) and a BSF width of 0.3 μm. The cell exhibited resistances of R_sh = 10⁶ Ω cm² and R_s = 1 Ω cm², along with a low defect density (N_t = 10¹⁰ cm^-3) in the ZnSnN₂ semiconductor. These factors combined to yield an impressive efficiency of 29.5%. Numerous studies on emerging ternary nitride semiconductors (Zn-IV-N₂) have highlighted ZnSnN₂ as a promising material for thin-film photovoltaics. This compound is appealing due to its abundance, non-toxicity, and cost-effectiveness. Unlike conventional solar cells that depend on rare, toxic, and costly elements, these components are still essential for today's solar cell technology.