Suppressing Ion Migration by Diaryliodonium Salt for Mixed Tin–Lead Perovskite Solar Cells and All-Perovskite Tandems

Mixed tin–lead (Sn–Pb) perovskites have garnered considerable interest owing to their optimal bandgap, which facilitates the development of high-performance single-junction and all-perovskite tandem solar cells notwithstanding, far less attention has been paid to ion migration and remains inadequately understood. Here, we demonstrate that severe ionic migration still occurs within Sn–Pb perovskites, which severely undermines the performance and stability of devices. The diphenyliodonium hexafluorophosphate (DPIHFP) as an additive was introduced into the perovskite film to anchor I– ions through electrostatic interactions. Besides, PF6– in DPIHFP could fill the iodine vacancies caused by I– ions migration and react with perovskite via hydrogen bonding interactions. The activation energy for ion migration within the device increased from 0.37 to 0.51 eV after the introduction of DPIHFP. In consequence, the resultant mixed Sn–Pb devices achieved remarkable efficiencies of over 23%, along with enhanced long-term stability. Additionally, two-terminal all-perovskite tandems using DPIHFP-doped Sn–Pb perovskite devices as the bottom cells achieved an efficiency exceeding 28%.