Dual-Site Crystallization Regulation for Highly Efficient and Stable Perovskite Solar Cells

Two-step sequential deposition method has been widely used to fabricate high-performance FAPbI3-based perovskite solar cells (PSCs). However, fast reaction between FAI and PbI2 always leads to an incomplete reaction and poor crystal quality. Here, 1-ethyl-3-methylimidazolium trifluoroacetate (EMIMTFA) is added to the FAI precursor solution, so as to regulate the crystallization behavior and obtain high-quality FAPbI3 perovskite films. The EMIMTFA can chemically interact simultaneously with FAI and PbI2, which will slow down the crystallization process of the perovskite film, achieving enlarged grain size, enhanced orientation and minimized defects, as well as less PbI2 residue. As a result, the PSCs with EMIMTFA achieve a champion efficiency of 24.31%, maintaining 90% of their initial efficiency after 1000 h under dark conditions in a N2-filled glove box. This study provides an efficient dual-site crystallization regulation strategy for the growth of high-quality FAPbI3 films.