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Kenneth Graham1 Alex Boehm1 So Min Park1

1, University of Kentucky, Lexington, Kentucky, United States

Organometal halide perovskites (OMHPs) have rapidly emerged as promising low-cost semiconductors for numerous applications, including photovoltaic cells and light emitting diodes. The energy of the valence band maximum, conduction band minimum, and transport gap are important parameters for fundamentally understanding the electronic properties of these materials and for successfully integrating these OMHPs into electronic devices. However, currently there is a large variation in literature reported valence and conduction band energies for almost all OMHPs, including the most widely studied OMHP, methylammonium lead iodide, where reported values for the valence band maximum range from 5.4 to 6.4 eV. These variations may potentially be attributed to differences in perovskite processing method, surface contamination, surface degradation, sample damage during the photoelectron spectroscopy measurement, or the method used to define the valence band maximum. In this talk I will present the use of a low-energy (10.2 eV) photon source and a low-energy (4-5 eV) detector for ultraviolet and inverse photoelectron spectroscopy measurements, respectively, of damage-prone materials. These low-energy photoelectron spectroscopy systems are shown to nearly eliminate sample damage and are used to probe the energetics of OMHPs as a function of both processing and composition. We find that the ionization energy and electron affinity for the same nominal material can vary based on the processing method and precursor used to produce the perovskite.

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