The nature of the methylamine–MAPbI3 complex: fundamentals of gas-induced perovskite liquefaction and crystallization

The liquefaction and recrystallization of CH3NH3PbI3 perovskite with methylamine – MA0/CH3NH2 gas in solar cells have been intensively studied in the past years, yet the exact mechanisms remained hypothesized and unclear due to lack of experimental evidence. The investigation presented in this work connects the interatomic bonding in the methylamine–MAPbI3 complex during liquefaction and recrystallization with the crystal morphology and the lifetime of photo-generated carriers in planar and mesoporous layer structures. Raman shift analysis and XRD structural investigation have been performed, showing that MA0 gas forms a complex with MAPbI3 via chemisorption of gas molecules to the perovskite crystal surface by replacing I− atoms in the PbI6 octahedra and via coordination of MA+. Through real-time photoluminescence, the changes in bonding during the liquid–solid transition are related to the radiative charge carrier recombination during the liquefaction and recrystallization. We found that the amount of MA0 gas reacting with perovskite determines the crystal morphology, pore-filling and, most importantly, the charge carrier lifetime.