Interplay of Mobile Ions and Injected Carriers Creates Recombination Centers in Metal Halide Perovskites under Bias

Abstract

We study the interaction of mobile ions and electronic charges to form nonradiative defects during electric biasing of methylammonium lead triiodide (MAPbI(3)) and forrnamidinium lead triiodide (FAPbI(3)) thin films. Using multimodal microscopy that combines in situ photoluminescence and scanning Kelvin probe microscopy in a lateral electrode geometry, we correlate temporal changes in radiative recombination with the spatial movement of ionic and electronic charge carriers. Importantly, we compare trap formation with both charge injecting and blocking contacts. Even though ion migration takes place in both cases, we observe the formation of new nonradiative defects in MAPbI(3) only in the presence of injected electrons, suggesting that redox processes play a key role. On the basis of density functional theory (DFT) simulations, we propose that reduction of Pb2+ to Pb-0 is responsible for the new defects formed in our films. These results underscore that defect properties in metal halide perovskites are not only determined by the migration of mobile ions but are also highly sensitive to their interaction with injected electronic charge.