Imaging Electron, Hole and Ion Transport in Halide Perovskite

Hybrid mixed halide perovskites are endowed with relatively high ionic motion and low electron mobility, which is surprising considering the high photovoltaic conversion efficiency they can allow. We here study electronic and ionic transport in hybrid mixed halide perovskites (MA,FA)Pb(I,Br)₃ using multi-dimensional luminescence imaging such as time-resolved and spectrally resolved imaging techniques. At short time scale (<1 µs) under pulsed electric bias, we could distinguish electron and hole transport using PL images in a situation where ion migration can be neglected. This resulted in the measurement of a 2-fold higher mobility for holes. At longer time (>1s) we observe the slower migration of ions that induces bandgap narrowing and defects creation, which we relate to halide accumulation at the positive electrode. The observed phenomena are relevant for perovskite-based PV & LED devices.