Interface-engineered SnS solar cells using an atomic-layer-deposited ZnSnO buffer layer

Abstract

Tin monosulfide (SnS) is a promising earth-abundant absorber for thin-film solar cells (TFSCs); however, interfacial recombination and poor junction quality severely limit device performance. In this work, we identify interfacial defect states and alkali-metal diffusion from the substrate as dominant loss pathways in vapor-transport-deposited SnS devices employing Cd-free oxide buffers. To mitigate these limitations, atomic-layer-deposited ZnSnO (ZTO) was integrated with sequence-controlled interface engineering using ultrathin ALD-ZnS passivation and CdSO4 wet treatment. This synergistic approach effectively suppresses interfacial recombination, limits Na diffusion, and improves junction uniformity, resulting in pronounced enhancements in fill factor and overall device performance. The optimized interface enabled a certified record efficiency of 4.938% in SnS solar cells. The broader applicability of this interface engineering approach was further validated in CZTSSe/ALD-ZTO devices, demonstrating its versatility across different chalcogenide absorber systems. These results establish a scalable and environmentally benign framework for interface control in chalcogenide photovoltaics.