Interfacial passivation of CdTe solar cells using Mg-doped SnO2 as electron transport layer for enhanced photovoltaic efficiency

Tin oxide (SnO2), known for its excellent optical and electronic properties, is increasingly favored as an electron transport layer(ETL) in high-efficiency thin film solar cells. However, its direct use in SnO2/CdTe heterojunction solar cells results in relatively low open-circuit voltage (VOC) and inferior power conversion efficiency (PCE). Herein, we achieve significantly high efficiency in CdTe-based photovoltaic devices by using Mg-doped SnO2 as ETLs, fabricated through magnetron co-sputtering technique. Capacitance–voltage (C–V) and space-charge-limited current measurements reveal that Mg doping significantly enhances the built-in potential at the SnO2/CdTe interface and reduces trap density over twofold. First-principles calculations indicate that the trap states originating from the Sn atom dangling bonds at the interface can be effectively passivated by the formation of MgSn defects, which are facilitated by Mg-doped SnO2. The resulting improvements in VOC and PCE are further validated through device simulations. This study demonstrates the potential of SnO2 as an ETL in high-efficiency CdTe solar cells and highlights the effectiveness of doping engineering in the contact layer for improving the interfacial properties of semiconductor devices.