Atomic-Layer-Deposited Interlayers Enabling Interfacial Band Tuning in Vapor Transport Deposition-SnS/CdS Solar Cells

Abstract Severe interfacial recombination remains a key barrier limiting carrier collection in SnS thin-film solar cells. Thus, in this study, atomic layer deposition (ALD)-based thin oxide interlayers are engineered at the SnS/CdS heterojunction. The applicability of ZnO, SnO2, and zinc tin oxide (ZTO) interlayers was probed to understand the interfacial electronic structure by systematically controlling the ALD process. The optimized condition within the investigated parameter range, corresponding to a 15 nm ZTO interlayer deposited at 120 °C, provides favorable interfacial band alignment, striking a balance between low transport resistance and favorable band alignment. The resulting SnS/ALD-ZTO/CdS solar cell achieved a power conversion efficiency of 4.45% (VOC = 0.326 V, JSC = 24.50 mA cm–2, FF = 56%), outperforming the 3.72% (VOC = 0.325 V, JSC = 21.30 mA cm–2, FF = 54%) baseline device without interlayer modification. UPS and XPS analyses confirm that 120 °C processing promotes favorable band offsets at the heterointerface governed by the well-coordinated Zn–Sn–O chemical environment. Dark J–V measurements support suppressed recombination, as evidenced by an approximately 2.4-fold reduction in the J0. This work demonstrates ALD-ZTO as an effective interface-engineering approach for high-performance SnS solar cells.