High-Efficiency All-Antimony Chalcogenide Tandem Solar Cells via Thermal-Evaporated CdS Interface Engineering

Abstract

Sb2S3, with an ideal bandgap of 1.7 eV, is a promising top-cell absorber for tandem solar cells (TSCs). However, CdS electron transport layers (ETLs) prepared via chemical bath deposition suffer from poor crystallinity and high roughness, inducing interfacial defects, parasitic absorption, and severe carrier recombination, which hinder device performance. To address these challenges, this study employs thermal evaporation (TE) to fabricate CdS ETLs for semi-transparent Sb2S3 solar cells. The TE-CdS films exhibit superior crystallinity, reduced roughness, and enhanced chemical purity. Sb2S3 films deposited on TE-CdS show preferential (hk1) orientation, improved crystallinity, optimized band alignment, and suppressed interfacial defects, facilitating efficient charge transport and light management. By incorporating a MoO3/ITO/Ag electrode, the semi-transparent Sb2S3 solar cell achieves a power conversion efficiency (PCE) of 7.46%, the highest reported efficiency for semi-transparent Sb2S3 solar cells. Furthermore, a four-terminal (4T) TSC, formed by mechanically stacking Sb2S3 and Sb2Se3 cells, attains the champion PCE of 10.51% for all-antimony chalcogenide-based TSCs. This study provides critical insights into ETL engineering for high-performance semi-transparent Sb-based solar cells and their tandem integration.