Effect of Organic Hole Transport Layer Energetics On Iodine Species Diffusion In Halide Perovskite Devices
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Iodine-containing species are major degradation products of halide perovskites under irradiation condition. However, iodine diffusion kinetics into and throughout organic hole transport materials (HTM) and consequent reactions are largely unexplored. Thus, we quantified I2 transmission rates through common organic HTMs. We observed I2 permeability to inversely correlate with HTM HOMO energy. Tracking electronic conductance during I2 vapor exposure confirms shallow HOMO HTMs are strongly oxidized (i.e., doped), leading to substantial I2 uptake and increased transmission rates. This suggest HTM energetics affect device stability; deeper HOMO energy HTMs will suppress iodine migration and associated degradation mechanisms.