SnO₂/In₂S₃ Dual Electron Transport Layer for Interface Defect Regulation and Band Engineering in Sb₂S₃ Solar Cells

Antimony sulfide (Sb2S3) is widely considered as an emerging photovoltaic absorber material due to its low cost, environmental friendliness, intrinsic stability, and abundance. In Sb2S3 photovoltaic devices, the electron transport layer (ETL) is indispensable for facilitating the efficient collection and transporting photogenerated electrons from the absorber layer to the electrode. Among various ETL materials, n-type CdS has been widely applied due to its excellent electron mobility. However, its inherent toxicity, high resistivity, and parasitic light absorption severely limit the performance of Sb2S3 photovoltaic devices. In recent years, indium sulfide (In2S3) has gained significant interest as an alternative ETL due to its robust chemical durability, low toxicity, excellent electron transport capability, and wide bandgap, which effectively blocks hole injection. Nonetheless, the In2S3 ETL alone suffers from severe interfacial recombination due to its interfacial defects and bad energy level matching with a transparent conductive glass electrode. In this work, first, we successfully synthesized In2S3 thin films via a facile, cost-effective, and environmentally friendly approach involving thermal decomposition of indium ethylxanthate (In(S2COEt)3) at 300 °C. Subsequently, the bilayer ETL (SnO2/In2S3) comprising SnO2 and In2S3 was incorporated into Sb2S3 solar cells to optimize interfacial properties and enhanced charge transport. The resulting device achieved the power conversion efficiency (PCE) of 3.91%, conspicuously higher than the 1.22% obtained with the single In2S3 ETL. The dual ETL creates a favorable energy level gradient, while the SnO2 interlayer facilitates the emergence of compact Sb2S3 films with improved crystallinity. This configuration mitigates charge recombination and facilitates electron extraction at the FTO/ETL interface, thereby boosting device performance. This work presents a strategy for constructing the dual ETL by thermally decomposing In(S2COEt)3 on SnO2, offering a cadmium-free, efficient, and environmentally friendly pathway to support the development of Sb2S3 photovoltaic devices.