Sn Perovskite Solar Cells via 2D/3D Bilayer Formation through a Sequential Vapor Process

Sn-based perovskite solar cells are attracting great attention because of their potential for efficiency enhancement and their relative eco-friendliness compared with Pb-based perovskite solar cells. The main challenges lie in improving the oxidation stability and ensuring a uniform morphology of the Sn-based perovskite films. Here, we introduce a bilayer structure of 2D PEA2SnI4 and 3D MASnI3 perovskite (PEA = phenethylammonium; MA = methylammonium) formed by a sequential vapor process that combines vacuum deposition and vapor reaction. The vapor process ensures that the perovskite thin films are uniform and enables the fabrication of an upper layer with fine thickness control without damaging the lower layer. With the introduction of the 2D layer, Sn oxidation is suppressed and the crystallinity of the 3D layer is enhanced. A planar-type solar cell fabricated using the optimized 2D/3D structure exhibits an average efficiency of 9.2 ± 0.2%.