Optimization of a High-Performance Cu2NiGeS4 Solar Cell with an SnS Back Surface Field

Abstract

Kesterite-type quaternary chalcogenides, particularly Cu2NiGeS4, are emerging as promising candidates for next-generation photovoltaics due to their earth-abundant and non-toxic constituents. However, the performance of Cu2NiGeS4-based devices is often limited by significant charge carrier recombination at the back interface. In this work, we investigate the impact of integrating a tin sulfide (SnS) layer as a Back Surface Field (BSF) to passivate this interface. By employing numerical simulations with the SCAPS-1D software, we model and systematically optimize an innovative ZnO:Al/ZnO/ZrS2/Cu2NiGeS4/SnS/Mo device architecture. The optimization of key physical parameters reveals that the inclusion of the SnS-BSF layer is critical for achieving high performance. Our final optimized device achieves a power conversion efficiency of 21.17%, with a high open-circuit voltage of 1.1009 V, a short-circuit current density of 22.89 mA/cm2, and an excellent fill factor of 83.99%. Analysis confirms that this performance enhancement is primarily attributed to the effective suppression of back surface recombination by the robust p-p+ heterojunction formed at the Cu2NiGeS4/SnS interface. These results validate the SnS-passivated Cu2NiGeS4 architecture as a highly promising pathway for developing efficient, low-cost, non-toxic and scalable photovoltaic technologies.