Stabilizing black-phase CsPbI_(3) under over 70% humidity

Recently,all-inorganic perovskites have attracted attention due to good thermal stability[1−12].Among them,CsPbI3 has the most desirable optical bandgap(~1.7 eV)for applications in optoelectronic devices[13−16].In general,making black-phase CsPbI3 film requires a high-temperature annealing up to 320℃[17,18],which inevitably raises energy consumption.Though being made at high temperature,the resulting black-phase(αorβphase)CsPbI3 film still suffers from an un-desirable phase transition under ambient conditions[19,20].Sev-eral strategies have been developed to lower the annealing temperature(90-100℃)[20−26],it is still challenging to stabilize black-phase CsPbI3 under ambient condition with high humidity and without a tedious annealing process.Herein,we developed a simple crystal redissolution(CR)strategy to make stable black-phase CsPbI3 film in ambient air with high humidity and without post-annealing.4-N,N-dimethylamino-4ʹ-Nʹ-methyl-stilbazolium tosylate(DAST)can chemically interact with CsPbI3 to reduce the formation energy of black-phase and inhibit CsPbI3 to undergo black-to-yellow phase transition.