Unravelling the role of vacancies in lead halide perovskite through electrical switching of photoluminescence

TL;DR

This paper investigates how ionic vacancies influence the electrical switching of photoluminescence in lead halide perovskite films, revealing ionic drift as a key factor in luminescence modulation.

Contribution

It introduces a dynamic transport model linking ionic vacancy drift to luminescence switching, providing a method to measure vacancy diffusion coefficients.

Findings

Ionic vacancy drift causes a sharp luminescence front in MAPbI3 films.

The reciprocal of current is linearly related to time, matching experimental data.

The diffusion coefficient of iodine vacancies is determined as 6×10^-9 cm^2/s.

Abstract

Methylammonium lead triiodide perovskite (MAPbI3) semiconductor displays outstanding photovoltaic and light emitting properties. We address the unique behavior in which a bias voltage can be used to switch on and off the luminescence of a planar film with lateral symmetric electrodes. Instead of a homogeneous suppression of emission, as in other organic semiconductor films, in MAPbI3 films a dark region advances from the positive electrode at a slow velocity of order of 1 um s-1. Here we explain the existence of the sharp front in terms of the drift of ionic vacancies that drastically reduce the radiative recombination rate in the film. Based on a dynamic transport model we show that the square reciprocal of the electrical current is linear with time in agreement with the experimental observations. This insight leads to a direct determination of the diffusion coefficient of iodine vacancies D = 6 10-9 cm2 s-1 and provides detailed information and control on the effect of ionic conduction over the electrooptical properties of hybrid perovskite materials.