Conformal PAA-Modified SnO2 Interfacial Layer for Efficient and Stable Sb2S3 Solar Cells

Sb2S3 is a promising thin-film photovoltaic absorber owing to its suitable band gap, high absorption coefficient, and earth-abundant composition. However, its performance remains limited by defect-induced carrier recombination and interfacial inhomogeneity at the electron transport layer (ETL)/Sb2S3 heterojunction, particularly when CdS is employed as an ETL. Herein, poly(acrylic acid) (PAA) with tailored molecular weight is introduced into the SnO2 colloidal solution to regulate nanoparticle dispersion and interfacial wettability, enabling the formation of a conformal and compact PAA-modified SnO2 interlayer on textured fluorine-doped tin oxide substrates. The optimized interlayer promotes the subsequent deposition of CdS films with improved surface uniformity and high-quality Sb2S3 absorbers with enhanced crystallinity. More importantly, the improved CdS/Sb2S3 interfacial integration suppresses defect-assisted recombination and prolongs the carrier lifetime, facilitating efficient charge transport. Consequently, the power conversion efficiency of Sb2S3 solar cells increased from 7.31% to 8.12%. In addition, the PAA-modified devices retain more than 91% of their initial efficiency after 100 days of ambient storage without encapsulation, significantly outperforming the control devices (80%). This work highlights the critical role of buried interface regulation in directing heterojunction growth and provides an effective interface engineering strategy for high-performance Sb2S3 photovoltaics.