Enhanced efficiency and stability in Sn-based perovskite solar cells with secondary crystallization growth

Abstract The conversion efficiencies reported for Tin (Sn) halide-based perovskite solar cells (PSCs) fall a large gap behind those of lead halide-based PSCs, mainly because of poor film quality of the former. Here we report an efficient strategy based on a simple secondary crystallization growth (SCG) technique to improve film quality for tin halide-based PSCs by applying a series of functional amine chlorides on the perovskite surface. They were discovered to enhance the film crystallinity and suppress the oxidation of Sn2+ remarkably, hence reduce trap state density and non-irradiative recombination in the absorber films. Furthermore, the SCG film holds the band levels matching better with carrier transport layers and herein favoring charge extraction at the device interfaces. Consequently, a champion device efficiency of 8.07% was achieved along with significant enhancements in Voc and Jsc, in contrast to 5.35% of the control device value. Moreover, the SCG film-based devices also exhibit superior stability comparing with the control one. This work explicitly paves a novel and general strategy for developing high performance lead-free PSCs.