Constructing the Electronic Structure of CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ Perovskite\nThin Films from Single-Crystal Band Structure\nMeasurements

Abstract

Photovoltaic\ncells based on halide perovskites, possessing remarkably\nhigh power conversion efficiencies have been reported. To push the\ndevelopment of such devices further, a comprehensive and reliable\nunderstanding of their electronic properties is essential but presently\nnot available. To provide a solid foundation for understanding the\nelectronic properties of polycrystalline thin films, we employ single-crystal\nband structure data from angle-resolved photoemission measurements.\nFor two prototypical perovskites (CH₃NH₃PbBr₃ and CH₃NH₃PbI₃), we reveal\nthe band dispersion in two high-symmetry directions and identify the\nglobal valence band maxima. With these benchmark data, we construct\n“standard” photoemission spectra from polycrystalline\nthin film samples and resolve challenges discussed in the literature\nfor determining the valence band onset with high reliability. Within\nthe framework laid out here, the consistency of relating the energy\nlevel alignment in perovskite-based photovoltaic and optoelectronic\ndevices with their functional parameters is substantially enhanced.