Degradable Additive Couple Enable Pure and Stable Alpha‐Phase FAPbI₃ for Perovskite Solar Cells

Abstract

AbstractPure black‐phase FAPbI3 has always been pursued because of its ideal bandgap (Eg) and high thermal stability. Here, a pair of sacrificial agents containing diethylamine hydrochloride (DEACl) and formamide (Fo) is reported, which can induce the oriented growth of black‐phase FAPbI3 along (111) and will disappear by the aminolysis reaction during perovskite annealing, retaining the Eg of FAPbI3 as 1.49 eV. In addition, the tensile strain of the target FAPbI3 is found to be mitigated with a stabilized black phase due to the tilt of FA+. The devices based on the pure and stable black‐phase (111)‐FAPbI3 achieved a power conversion efficiency of 25.2% and 24.2% (certified 23.51%) with an aperture area of 0.09 and 1.04 cm2, respectively. After 1080 h of operation at the maximum power point under 1‐sun illumination (100 mW cm−2), the devices maintained 91.68 ± 0.72% of the initial efficiencies.