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

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.