Luminescent Intermediates and Humidity-Dependent RoomTemperature Conversion of the MAPbI3 Perovskite Precursor

摘要

Preparation of metal-halide perovskites underroom temperature attracts attention because of energy savingby removing thermal annealing. Room-temperature transformation of spin-cast wet films consisting of methylammonium (MA) iodide, PbI2, and dimethylformamide toward solidMAPbI3 perovskite proceeds via several intermediate crystalline states and is strongly dependent on ambient humidity.Light transmission and photoluminescence (PL) microscopyand spectroscopy were used to monitor the growth of crystalsand transformation of their properties in time under nitrogenatmosphere at room temperature. Under low humidity, a highly luminescent intermediate phase with low absorption in thevisible range appears, with the PL spectra composed of several bands in the range from 600 to 760 nm. We assign these bands tolow-dimensional (nanocrystals and two-dimensional inclusions) MAPbI3 intermediates, where the exciton confinement shiftsthe spectrum to higher energies in comparison with the bulk MAPbI3. The intermediate levels of ambient humidity (10?50%)appear to catalyze the conversion of the intermediate phase to MAPbI3. At a high ambient humidity (>80%), the initiallyformed MAPbI3 is quickly transformed to the transparent hydrate phase of MAPbI3. The role of ambient water catalyzing thematerial transformation by competing for Pb coordination with the solvent molecules is discussed.