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

Pure black-phase FAPbI₃ has always been pursued because of its ideal bandgap (E_g) 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 E_g 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.