Ion Mobility Independent Large Signal Switching of Perovskite Devices

TL;DR

This study reveals that large signal switching delays in perovskite devices are governed by electronic dipoles, not ionic mobility, challenging previous assumptions and impacting device optimization.

Contribution

It demonstrates that switching delays are independent of ion mobility and driven by electronic dipoles, supported by simulations and experimental data.

Findings

Switching delays are dictated by electronic dipoles.

Terminal currents reach steady state before ionic relaxation.

Ionic mobility does not influence large signal switching delays.

Abstract

The presence of mobile ions in perovskites is well known to influence the device electrostatics leading to a wide variety of anomalous characteristics related to hysteresis, efficiency degradation, low frequency capacitance, large signal switching, etc. Accordingly, the ion mobility is understood to a have a critical influence on the associated time constants/delays. Quite contrary to this broadly accepted thought, here we show that the time delays associated with large signal switching show a universal behavior dictated by electronic dipoles, rather than ionic dipoles. Due to the resultant sudden and dramatic collapse of contact layer depletion region, switching delays are independent of ion mobilities! Further, our detailed numerical simulations, well supported by experimental results, indicate that terminal currents show near steady state behavior well ahead of the relaxation of ionic distributions to their steady state conditions. These results have interesting implications towards the understanding and optimization of perovskite based electronic devices, including solar cells and LEDs.