The nature of the methylamine-MAPbI3complex: fundamentals of gas-induced perovskite liquefaction and crystallization

Abstract

The liquefaction and recrystallization of CH3NH3PbI3perovskite with methylamine - MA0/CH3NH2gas 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-MAPbI3complex 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 MA0gas forms a complex with MAPbI3viachemisorption of gas molecules to the perovskite crystal surface by replacing I-atoms in the PbI6octahedra andviacoordination 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 MA0gas reacting with perovskite determines the crystal morphology, pore-filling and, most importantly, the charge carrier lifetime.