Charge Transfer Dynamics of Phase-Segregated Halide Perovskites: CHNHPbCl and CHNHPbI or (CHNH)(CHNH) Pb I Mixtures.

Lead halide perovskites present a versatile class of solution-processable semiconductors with highly tunable bandgaps that span ultraviolet, visible, and near-infrared portions of the spectrum. We explore phase-separated chloride and iodide lead perovskite mixtures as candidate materials for intermediate band applications in future photovoltaics. X-ray diffraction and scanning electron microscopy reveal that deposition of precursor solutions across the MAPbCl/MAPbI composition space affords quasi-epitaxial cocrystallized films, in which the two perovskites do not alloy but instead remain phase-segregated. First-principle calculations further support the formation of an epitaxial interface and predict energy offsets in the valence band and conduction band edges that could result in intermediate energy absorption. The charge dynamics of variable mixtures of the relatively narrow bandgap (1.57 eV) MAPbI perovskite and wide bandgap (3.02 eV) MAPbCl are probed to map charge and energy flow direction and kinetics. Time-resolved photoluminescence and transient absorption measurements reveal charge transfer of photoexcited carriers in MAPbCl to MAPbI in tens of picoseconds. The rate of quenching can be further tuned by replacing MAPbI with two-dimensional Ruddlesden-Popper (BA)(MA) Pb I ( n = 3, 2, and 1) perovskites, which also remain phase-separated.