Numerical Optimization of a Highly Efficient Two Terminal CZTS–ZnSnAs 2 ‐Based Tandem Solar Cell

This study theoretically investigates a novel two‐terminal Cu 2 ZnSnS 4 (CZTS)–ZnSnAs 2 tandem solar cell using SCAPS‐1D simulation. The wide‐bandgap CZTS (1.5 eV) acts as the top absorber, while narrow‐bandgap ZnSnAs 2 (0.76 eV) captures near‐infrared light in the bottom cell. Optimized CdS window and BSF layers (CGS for the top, WSe 2 for the bottom) enhance carrier collection and suppress recombination. This simulation assumed zero optical losses, ideal tunnel junction, and negligible series resistance. Through parametric optimization of thickness, doping, and defects, current matching is achieved, yielding a J SC = 26.31 mA/cm 2 , a V OC = 1.77 V, an FF = 83.85%, and a PCE = 39.2%, with spectral response up to 1632 nm. This sustainable tandem design offers a high‐efficiency, low‐cost alternative to conventional multijunction photovoltaics (PVs).