Precursor Engineering of the Electron Transport Layer for Application in High‐Performance Perovskite Solar Cells

Abstract The electron transport layer (ETL) is a key component of regular perovskite solar cells to promote the overall charge extraction efficiency and tune the crystallinity of the perovskite layer for better device performance. The authors present a novel protocol of ETL engineering by incorporating a composition of the perovskite precursor, methylammonium chloride (MACl), or formamidine chloride (FACl), into SnO 2 layers, which are then converted into the crystal nuclei of perovskites by reaction with PbI 2 . The SnO 2 ‐embedded nuclei remarkably improve the morphology and crystallinity of the optically active perovskite layers. The improved ETL‐to‐perovskite electrical contact and dense packing of large‐grained perovskites enhance the carrier mobility and suppress charge recombination. The power conversion efficiency increases from 20.12% (blank device) to 21.87% (21.72%) for devices with MACl (FACl) as an ETL dopant. Moreover, all the precursor‐engineered cells exhibit a record‐high fill factor (82%).