Ultrathin SnO₂ Buffer Layer Aids in Interface and Band Engineering for Sb₂(S,Se)₃ Solar Cells with over 8% Efficiency

The environmentally friendly antimony selenosulfide (Sb2(S,Se)3) semiconductor emerges as a promising light harvester for thin-film photovoltaics owing to its excellent material and optoelectronic properties. The alloyed Sb2(S,Se)3 is endowed with the complementary benefits of Sb2S3 and Sb2Se3, such as a tunable band gap within the range of 1.10–1.70 eV. In Sb2(S,Se)3 solar cells, the n-type semiconductor CdS is extensively used as an electron transport layer (ETL), which plays a role in extracting photogenerated electrons from absorbers and transporting them to conducting substrates. However, the unsatisfactory ETL/absorber interface contact often involves severe interface recombination. Herein, we report that an ultrathin SnO2 buffer layer of ∼10 nm applied on the high-roughness fluorine-doped tin oxide (FTO) substrate aids in effective interface and band engineering for superstrate CdS/Sb2(S,Se)3 solar cells. Careful characterizations confirm that the ultrathin SnO2 buffer layer plays a positive role in inhibiting the shunt current leakage at the ETL/absorber interface and manipulating the cascade energy band structure for more effective interface passivation and efficient electron extraction. Consequently, the resultant SnO2/CdS ETL-based Sb2(S,Se)3 solar cells exhibited a remarkable device efficiency of 8.67%, coupled with a considerable open-circuit voltage of 0.72 V. Our finding demonstrates a facile approach to engineer the interface contact and band offset to accelerate electron extraction, transport, and collection efficiencies.