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 FAPbI
₃
-based perovskite solar cells (PSCs). However, fast reaction between FAI and PbI
₂
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 FAPbI
₃
perovskite films. The EMIMTFA can chemically interact simultaneously with FAI and PbI
₂
, which will slow down the crystallization process of the perovskite film, achieving enlarged grain size, enhanced orientation and minimized defects, as well as less PbI
₂
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 N
₂
-filled glove box. This study provides an efficient dual-site crystallization regulation strategy for the growth of high-quality FAPbI
₃
films.