# Substrate-dependent Photoconductivity Dynamics in a High-efficiency Hybrid Perovskite Alloy

## TL;DR

This study investigates how different substrates affect the photoconductivity dynamics of a specific hybrid perovskite film, revealing substrate-dependent ionic and electronic behaviors with implications for device stability.

## Contribution

It provides the first detailed analysis of substrate-dependent photoconductivity and ionic-electronic interactions in hybrid perovskite films using microcantilever measurements.

## Key findings

- High and light-independent conductivity over ITO and NiO.
- Light-induced conductivity persists for tens of seconds on TiO₂ and SnO₂.
- Conductivity recovery over TiO₂ shows activated temperature dependence.

## Abstract

Films of (FA$_{0.79}$MA$_{0.16}$Cs$_{0.05}$)$_{0.97}$Pb(I$_{0.84}$Br$_{0.16}$)$_{2.97}$ were grown over TiO$_{2}$, SnO$_{2}$, ITO, and NiO. Film conductivity was interrogated by measuring the in-phase and out-of-phase forces acting between the film and a charged microcantilever. We followed the films' conductivity vs. time, frequency, light intensity, and temperature (233 to 312 K). Perovskite conductivity was high and light-independent over ITO and NiO. Over TiO$_{2}$ and SnO$_{2}$, the conductivity was low in the dark, increased with light intensity, and persisted for 10's of seconds after the light was removed. At elevated temperature over TiO$_{2}$, the rate of conductivity recovery in the dark showed an activated temperature dependence (E$_{a}$ = 0.58 eV). Surprisingly, the light-induced conductivity over TiO$_{2}$ and SnO$_{2}$ relaxed essentially instantaneously at low temperature. We use a transmission-line model for mixed ionic-electronic conductors to show that the measurements presented are sensitive to the sum of electronic and ionic conductivities. We rationalize the seemingly incongruous observations using the idea that holes, introduced either by equilibration with the substrate or via optical irradiation, create iodide vacancies.