Metal halide perovskite materials with the formula APbX3 (A is a cation; X is a halogen) are leading the pack of solution-processed semiconductors for solar cells and optoelectronics. A key to the success of these materials is their hallmark long radiative charge carrier lifetimes, which allows carriers to be collected as useful charges before recombining. Herein, we grew high-quality single crystal perovskites of A= methylammonium, formamidinium, and Cs, and X=I and Br; and used time-resolved photoluminescence (at low excitation fluence upon two-photon excitation), together with temperature dependent optical and structural characterization techniques to study the radiative charge carrier lifetimes and their relationship to crystal structure and composition. We uncover compositions with long carrier lifetimes (a few microseconds) and others with ultralong lifetimes (tens of microseconds). We combine experiment and modeling to showcase the differing roles played by the cation units and halides in modulating the carrier lifetimes and the defect formation energies of the perovskites.
Our work paves the way for rationally tailoring perovskite materials properties for optoelectronics through compositional design and selection.