1Cd Free SnO ₂ /TiO ₂ Electron Transport Layer for SnS Thin‐Film Solar Cells

Group IV‐VI semiconductor tin sulfide (SnS) has garnered considerable research interest due to its suitable bandgap alignment with silicon, coupled with inherent advantages including environmental compatibility, operational safety, and excellent light absorption characteristics. The electron transport layer (ETL) constitutes a critical determinant in optimizing the performance of SnS solar cells. Herein, a glass/fluorine‐doped tin oxide (FTO) substrate is employed to fabricate four ETL architectures, comprising SnO 2 , TiO 2 , SnO 2 /TiO 2 , and TiO 2 /SnO 2 , through spin‐coating methodology, subsequently serving as ETLs for SnS photovoltaic devices. The absorber layer is systematically deposited via vapor transport deposition (VTD) to construct glass/FTO/ (50 nm) SnO 2 /(50 nm) TiO 2 /(≈200 nm) SnS /spiro‐OMeTAD/Au device architectures. Comprehensive investigations reveal crucial correlations between deposition temperatures and SnS film characteristics, particularly demonstrating that optimized VTD processing enables the formation of high‐crystallinity SnS layers with enhanced light‐harvesting capabilities. The systematic material characterization of hetero‐interface engineering between ETLs and SnS absorbers uncovered synergistic interfacial charge transfer mechanisms. The optimized device exhibits a short‐circuit current density ( J sc ) of 21.4 mA cm −2 , open‐circuit voltage ( V oc ) of 323 mV, fill factor of 0.36, and power conversion efficiency of 1.92%. In this work, Cd‐free devices are fabricated using a simplified processing scheme, offering cost‐effective and environmentally sustainable advantages.