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Alex Boehm1 Kenneth Graham1

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

Metal halide perovskites (MHPs) and organometal halide perovskites (OMHPs) display enormous potential as next generation materials for optoelectronics, such as photovoltaics, lasers, and light emitting diodes. MHPs and OMHPs cover a diverse range of chemical compositions; however, the current highest performing (O)MHPs in photovoltaics include lead, a well-known toxic metal. Recent studies show that lead’s group 14 neighbor, tin, is also suitable for use in photovoltaics as a low-cost and environmentally friendly lead alternative. Like their lead counterparts, tin perovskites can have a range of chemical compositions consisting of numerous A and X site ions. Early investigations have primarily examined the influence of A and X site ions on the photovoltaic performance and optical properties of these tin-based perovskites. However, the continual development of tin (O)MHPs necessitates accurate determination of their electronic structures. Ultraviolet photoelectron spectroscopy (UPS) and inverse photoelectron spectroscopy (IPES) are complimentary techniques that provide a direct means for probing occupied and unoccupied electronic states in semiconducting materials. Here we present a novel VUV photon source for UPS measurements, a low-energy IPES system, and the application of these systems to probe the valence and conduction band energies of tin based (O)MHPs as a function of composition. Our VUV photon source utilizes H Lyman-α emission with narrow linewidth, broad tunable intensity, and lower background compared to typical UPS sources. This, in conjunction with our newly developed low energy IPES system, allows us to perform measurements without risk of sample degradation and gain a complete picture of material and interfacial energetics.

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