Interplay between Iodide and Tin Vacancies in CsSnI3 Perovskite Solar Cells

Tin-based perovskite materials have the drawbacks of high density of Sn vacancies, structural deformations of SnI 6 – octahedra, and oxidation of unstable Sn 2+ states, resulting in poor chemical stability processed at inert and open atmosphere. In this work, we demonstrate the temperature effects on reduction of Sn vacancies (V sn ) in polymorphic CsSnI 3 perovskite solar cells. Evidence of light-induced I – ion diffusion and an interplay between iodide and Sn vacancies were briefly presented. We have observed by X-ray photoelectron spectroscopy that the formation of iodide vacancies (V I ) are highly activated at 60 °C, contributing to the reduction of acceptor defects, mainly Sn vacancies (V sn ). The formation of SnO – and SnO 2 – at high temperature mitigates the Sn–I interaction and eventually increases the trap density at Au/CsSnI 3 interfaces. We have observed by time-of-flight secondary ion mass spectrometry that the delocalized I – ions are accumulated near the metal contacts and form AuI – ions which diffuse through the material, inhibiting the exciton transport.