Interplay between Ion Transport, Applied Bias, and Degradation under Illumination in Hybrid Perovskite p-i-n Devices

We studied ion transport in hybrid organic inorganic perovskite p-i-n devices as a function of applied bias under device operating conditions. Using electrochemical impedance spectroscopy (EIS) and equivalent circuit modeling, we elucidated various resistive and capacitive elements in the device. We show that ion migration is predictably influenced by a low applied forward bias, characterized by an increased capacitance at the hole-transporting (HTM) and electron transporting material (ETM) interfaces, as well as in bulk. However, unlike observations in n-i-p devices, we found that there is a capacitive discharge leading to ion redistribution in the bulk at high forward biases. Furthermore, we show that a chemical double-layer capacitance buildup as a result of ion accumulation impacts the electronic properties of the device, likely by inducing either charge pinning or charge screening, depending on the direction of the ion-induced field. Lastly, we extrapolate ion diffusion coefficients (similar to 10(-7) cm(2) s(-1)) and ionic conductivities (,similar to 10(-7) S cm(-1)) from the Warburg mass (ion) diffusion response and show that, as the device degrades, there is an overall depletion of capacitive effects coupled with increased ion mobility.