In situ investigation of interfacial properties of Sb2Se3 heterojunctions

Abstract

Antimony selenide (Sb2Se3), emerging as a promising photovoltaic material, has achieved over 9% efficiency within only 6 years. Various kinds of buffer materials are employed for Sb2Se3 solar cells to construct heterojunctions with distinctive device performance. Herein, we introduce in situ high resolution photoemission spectroscopy (HRPES) to investigate the interfacial properties between Sb2Se3 and three types of widely adopted buffer layers: CdS, ZnO, and TiO2. HRPES results and theoretical thermodynamic calculations reveal that in the initial stage, the deposited Sb2Se3 reacts with buffer materials in terms of activity in the following order: CdS ≥ ZnO > TiO2. Distinct transition layers are formed at CdS/Sb2Se3 and ZnO/Sb2Se3 interfaces, whereas it is nearly absent at TiO2/Sb2Se3. Our results suggest that the CdS/Sb2Se3 heterojunction shows spike-like conduction band offsets (CBOs), whereas ZnO/Sb2Se3 demonstrates a cliff-like CBO, and TiO2/Sb2Se3 is almost flat. The transition layers and band alignments at the interface could be the reasons for the stability and performance of Sb2Se3 photovoltaic devices with different buffer materials. Our investigation deepens the understanding of Sb2Se3 heterojunction formation and can benefit further development of Sb2Se3 thin-film solar cells.