Photoluminescence Loss and Recovery of α-CsPbI Quantum Dots Originated from Chemical Equilibrium Shift of Oleylammonium.

α-CsPbI perovskite quantum dots (PQDs) have great potentials in red-emitting LED and solar cell applications. However, their instability with quick photoluminescence loss with time greatly limits their development. In this study, we found that the nonluminous aged α-CsPbI PQDs instantly regained fluorescence emission after a surface treatment with trioctylphosphine. Meanwhile, this surface treatment also worked on fresh α-CsPbI PQDs to enhance photoluminescence emission. The structures and compositions of fresh and aged PQDs before and after surface treatment were analyzed in detail. We demonstrated that a surface chemical equilibrium shift mechanism involving oleylammonium led to the PL loss and recovery of α-CsPbI PQDs. This chemical equilibrium shift also played an important role in other PQD stabilities against long-term storage, temperature, UV irradiation and ethanol, which were all significantly improved after treatment. The treated α-CsPbI PQDs were phase stable for more than 6 months. Oleic acid and oleylamine are common ligands used in PQD syntheses; this study shall promote the understanding of PQD surface chemistry and the preparation of stable α-CsPbI PQDs.