Investigation of Cd-Free Sb2Se3 Thin-Film Solar Cells by ALD-ZnSnO Electron Transport Layer

Most of the efficient Sb2Se3-based PV devices use CdS as electron transport layer (ETL) or/and an organic hole transport layer. With the objective of fabricating non-toxic and stable solar cells, we investigate substrate Sb2Se3 thin-film PV devices by the replacement of CdS by Zn1-xSnxO (ZTO) layer without using an organic material in the device structure. In this work, Sb2Se3 thin films have been grown by selenization of evaporated Sb layer onto Mo/SLG substrates. ZTO films are fabricated by atomic layer deposition (ALD) to develop Cd-free solar cells, while the reference CdS layer is deposited by chemical bath. The absorber presents an orthorhombic structure with [hk1] preferred orientation, and a compact structure free of pinholes. The different techniques used for the fabrication of the ETLs show the different CdS and ZTO morphologies, with a conformal growth and uniform surface for the ZTO. ITO/ZnO/CdS/Sb2Se3/Mo/SLG and ITO/ZnO/ZnSnO/Sb2Se3/Mo/SLG solar cells are fabricated. A total efficiency of 4.3 % for the CdS/Sb2Se3 solar cell and of 3.0 % for the Cd-free PV device are obtained. It is revealed that ZTO thickness is a critical parameter to optimize the heterojunction. In this work, 40 nm ZTO layer leads to higher device performances.