Controlling Orientation Diversity of Mixed Ion Perovskites: Reduced Crystal Microstrain and Improved Structural Stability.

Formamidinium lead iodide (FAPbI3)-based perovskite has attracted increasing attention of researchers due to its lower band gap and improved thermal stability. However, it is structurally unstable and easy to phase-transfer at room temperature. Here, we improve the structural stability of perovskite by controlling its orientation diversity. XRD results show that incorporating CsBr into FAPbI3 is effective to adjust the crystal plane stacking. For the first time, an orientation diversity factor (ODF) is identified, and it is found that an increased ODF is propitious to decrease the lattice distortion and relax the microstrain in the crystal, boosting the efficiency and stability of the perovskite solar cells (PSCs). The optimized inverted PSC based on FA0.85Cs0.15PbI2.85Br0.15 achieves efficiency of 17.59% and presents ignored performance decline under continuous light-soaking for 500 h.