Chasing Charge Carriers: Diffusion Dynamics in Mixed-n Quasi-Two-Dimensional Colloidal MAPbBr3 Perovskites

TL;DR

This study investigates charge carrier diffusion in different colloidal MAPbBr3 perovskite nanocrystals using FLIM, revealing subdiffusive behavior and varying diffusivities across morphologies, which informs optoelectronic device design.

Contribution

It introduces a detailed analysis of charge diffusion dynamics in mixed-n colloidal perovskite nanocrystals with different morphologies using time-resolved fluorescence imaging.

Findings

Subdiffusive charge transport observed in all nanocrystal morphologies.

Bulk-like nanostripes exhibit the highest carrier diffusivity.

Morphology significantly influences charge migration and trapping behaviors.

Abstract

In optoelectronic applications, metal halide perovskites (MHPs) are compelling materials because of their highly tuneable 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 behaviours. We characterized three different methylammonium lead tribromide perovskite (MAPbBr3) morphologies: nanoplatelets (NPLs), nanosheets (NSs), and nanostripes (NSTs) 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 was employed to quantify the charge carriers' migration process upon photoexcitation. The results are rationalized in the two-dimensional diffusion model framework, considering funnelling and trapping processes in mixed-n colloidal MHPs. Subdiffusion mode was found to prevail in the nanocrystals, whereby the highest carrier diffusivity was 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.