Molecular Beam Epitaxy Deposition of In Situ O‐Doped CdS Films for Highly Efficient Sb₂(S,Se)₃ Solar Cells

Abstract Antimony selenosulfide (Sb₂(S,Se)₃) is considered as a promising light‐harvesting material and has been widely used in solar cells. For high‐efficiency Sb₂(S,Se)₃ solar cells, the most commonly used electron‐transporting layer of cadmium sulfide (CdS) is generally prepared by chemical bath deposition (CBD) approach. However, the hazardous waste liquid from the chemical bath and the sensitivity of the deposition process to the environment are challenges to practical applications. Herein, a molecular beam epitaxy deposition is reported to prepare CdS films, overcoming the drawbacks of CBD process. Furthermore, through introducing oxygen during the deposition of CdS, the sulfur vacancy defects generated in the vacuum deposition process are suppressed. The performance of Sb₂(S,Se)₃ solar cells is accordingly improved significantly. This improvement is attributed to the following aspects: i) the improved optical transmittance of CdS films. ii) The enhanced [hk1] orientation of Sb₂(S,Se)₃ absorber layer. iii) The improved heterojunction quality and suppressed carrier recombination. As a result, a power conversion efficiency of 8.59% for Sb₂(S,Se)₃ solar cells is achieved. This study provides a novel strategy for preparing electron‐transporting layers for efficient chalcogenide thin‐film solar cells and sheds new light on large‐area solar cell applications.