Heterojunction interface engineering enabling high transmittance and record efficiency in Sb2S3 semitransparent solar cell

Antimony sulfide (Sb₂S₃) is an auspicious contender for semitransparent and tandem solar cells owing to its exceptional optoelectronic characteristics. Yet, complex bulk and heterojunction defects hinder achieving optimal power conversion efficiency (PCE). Although CdS is an established electron transport layer (ETL) in Sb-chalcogenide solar cells benefitting from its exceptional electron mobility (350 cm²V^–1s⁻¹) and energy level alignments, its potential contribution has been deplorably overlooked in Sb₂S₃ semitransparent photovoltaics (STPV). Herein, an optimized TiO₂/CdS double ETL strategy is embraced to counteract CdS absorption loss and mitigate the “deep cliff” conduction band off-set at TiO₂/Sb₂S₃ heterojunction. Subsequently, an evolved chemical bath deposition strategy is proposed to deposit a uniform, faster, and comparatively more transparent Sb₂S₃ absorber layer. A systematic investigation of the absorber layer and in-depth analysis of carrier dynamics at heterojunctions advocate for the mitigation of charge accumulation and recombination at the interface, thereby pledging superior carrier transport. The advantageous gradient energy band alignment of TiO₂/CdS/Sb₂S₃ realized a record PCE of 5.61 % for STPV. Furthermore, the semitransparent device is innovatively employed as a window, enabling transmitted light to be harvested by subsequent Sb₂S₃ solar cells. It maintains 18 % of its standalone PCE, thereby setting new benchmarks for its practical submissions.