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

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.