LAUSR

The promising tin perovskite solar cells (PSCs) suffer from the oxidation from Sn2+ to Sn4+, leading to a disappointed conversion efficiency far from what they deserve, along with poor stability. In this work, PEABr is employed to form an ultrathin-low-dimensional perovskite layer on the surface of FASnI3 absorber film to improve the interface of perovskite/PCBM in the inverted planar device structure of "ITO/PEDOT:PSS/perovskite/PCBM/BCP/electrode". The device efficiency has been enhanced from 4.77% to 7.86% by this PEABr treatment. A series of characterizations prove that this modification can improve the crystallinity of the FASnI3 perovskite by incorporating Br and form an ultrathin-low-dimensional perovskite layer at the interface which leads to the effective suppression of Sn2+ oxidation, the improved band level alignment and the decrease of the defect density. Those effects contribute to the obvious enhancement of device conversion efficiency. Moreover, this treatment also leads to remarkably enhanced device stability with approximate 80% of initial efficiency after 350 hours' light soaking while the control device fails within 140 hours. This work definitely deepens our understanding to the suppression effect of PEABr on the oxidation of Sn2+ and paves a new way to fabricate promising tin halide PSCs by facile interface engineering.