Optoelectronic Properties of Mixed Iodide-Bromide Perovskites from First-Principles Computational Modeling and Experiment

Halogen mixing in lead-halide perovskites is an effective route for tuning theband gap in light emission and multijunction solar cell applications. Here we report the effectof halogen mixing on the optoelectronic properties of lead-halide perovskites from theory andexperiment. We applied the virtual crystal approximation within density functional theory, theGWapproximation, and the Bethe-Salpeter equation to calculate structural, vibrational, andoptoelectronic properties for a series of mixed halide perovskites. We separately performspectroscopic measurements of these properties and analyze the impact of halogen mixing onquasiparticle band gaps, effective masses, absorption coefficients, charge-carrier mobilities,and exciton binding energies. Our joint theoretical-experimental study demonstrates thatiodide-bromide mixed-halide perovskites can be modeled as homovalent alloys, and localstructural distortions do not play a significant role for the properties of these mixed species.Our study outlines a general theoretical-experimental framework for future investigations ofnovel chemically mixed systems.