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Our recent drift-diffusion simulations indicate that the electrostatic potential arising from mobile ion redistribution controls electronic charge transfer processes such as recombination in mixed conducting lead halide perovskite devices and can give rise to apparent capacitive behavior.[1] The capacitive features of a mixed conductor are traditionally described within equivalent circuit models by a chemical capacitance, which accounts for bulk polarization effects.[2, 3] and scales with the thickness of the device, complemented by an interfacial capacitance, related to electronic and ionic accumulation at the interfaces with the contacts. Since the effect described is not simply associated with an accumulation or depletion of charges in the active layer, it cannot be adequately described with a conventional capacitor. We identify the bipolar transistor as a most appropriate circuit element to reproduce analytically the …