Chasing Charge Carriers: Diffusion Dynamics in Mixed-n Quasi-2D Colloidal MAPbBr3 Perovskites

Abstract

In optoelectronic applications, metal halide perovskites (MHPs) are compelling materials because of their highly tunable and intensely competitive optical properties. Colloidal synthesis enables the controlled formation of various morphologies of MHP nanocrystals, all with different carrier properties and, hence, different optical and carrier transport behaviors. Three different methylammonium lead tribromide perovskite (MAPbBr3) morphologies: nanoplatelets (NPLs), nanosheets (NSs), and nanostripes (NSTs) are characterized and synthesized by hot-injection synthesis protocols with slightly different parameters. A fluorescence imaging microscope (FLIM) for time- and space-resolved measurements of the carrier migration is employed to quantify the charge carriers’ migration process upon photoexcitation. The results are rationalized in the 2D diffusion model framework, considering funneling and trapping processes in mixed-n colloidal MHPs. Subdiffusion mode is found to prevail in the nanocrystals, whereby the highest carrier diffusivity is found for bulk-like NSTs, followed by layered NSs and a film of NPLs. These findings provide a better understanding of optoelectronic processes in perovskites relevant to photovoltaic and light-emitting devices.