Elucidating the long-range charge carrier mobility in metal halide perovskite thin films

TL;DR

This paper introduces a combined optical and electrical measurement technique to accurately determine long-range charge carrier mobility in lead halide perovskite films, revealing significant differences based on fabrication methods.

Contribution

A novel measurement approach that simultaneously evaluates conductivity and charge density to accurately assess lateral mobility in perovskite films.

Findings

Lateral mobility in MAPbI3 is approximately 2 cm²/Vs.

Mobility varies from 2.2 to 0.2 cm²/Vs across different fabrication methods.

First accurate measurement of long-range charge mobility in lead halide perovskite films.

Abstract

Many optoelectronic properties have been reported for lead halide perovskite polycrystalline films. However, ambiguities in the evaluation of these properties remain, especially for long-range lateral charge transport, where ionic conduction can complicate interpretation of data. Here we demonstrate a new technique to measure the long-range charge carrier mobility in such materials. We combine quasi-steady-state photo-conductivity measurements (electrical probe) with photo-induced transmission and reflection measurements (optical probe) to simultaneously evaluate the conductivity and charge carrier density. With this knowledge we determine the lateral mobility to be ~ 2 cm2/Vs for CH3NH3PbI3 (MAPbI3) polycrystalline perovskite films prepared from the acetonitrile/methylamine solvent system. Furthermore, we present significant differences in long-range charge carrier mobilities, from 2.2 to 0.2 cm2/Vs, between films of contemporary perovskite compositions prepared via different fabrication processes, including solution and vapour phase deposition techniques. Arguably, our work provides the first accurate evaluation of the long-range lateral charge carrier mobility in lead halide perovskite films, with charge carrier density in the range typically achieved under photovoltaic operation.