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

Abstract Pure black‐phase FAPbI 3 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 FAPbI 3 along (111) and will disappear by the aminolysis reaction during perovskite annealing, retaining the E g of FAPbI 3 as 1.49 eV. In addition, the tensile strain of the target FAPbI 3 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)‐FAPbI 3 achieved a power conversion efficiency of 25.2% and 24.2% (certified 23.51%) with an aperture area of 0.09 and 1.04 cm 2 , 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.