Sulfur-Vacancy Passivation in Solution-Processed Sb2S3 Thin Films: Influence on Photovoltaic Interfaces

Abstract

We have presented a modified two-step sequential deposition method in forming Sb2S3 thin films. In contrast to conventional chemical bath deposition (CBD) route, this sequential deposition approach has allowed passivation of sulfur vacancies in Sb2S3 through a control over precursor stoichiometry (S/Sb ratio) during the film formation. We have made an in-depth characterization of the chalcogenide thin films upon passivation of the vacancies. While a sulfur-deficient composition led to the formation of donor-like sulfur vacancies, a sulfur-rich stoichiometry passivated such vacancies followed by creation of sulfur antisite defects in the chalcogenide. Scanning tunneling spectroscopy and thereby density of states allowed us to locate individual band-energies and their dependence on defect passivation. A strong dependence of optical bandgap and surface morphology of the Sb2S3 layer on the precursor stoichiometry was evidenced in our study, and an optimized balance between the parameters was estimated for a slightly sulfur-rich composition (S/Sb ratio of 1.2). Interestingly, the photovoltaic parameters of Cu:NiO/Sb2S3/PCBM planar heterojunctions excelled at the predicted stoichiometry, yielding a power conversion efficiency of 3.02% along with a significantly high open-circuit voltage of 0.8 V. This effort thus provides new insights into the influence of defect passivation on solar cell characteristics based on solution-processed Sb2S3 thin films.