Imaging the Long Transport Lengths of Photo-generated Carriers in Oriented Perovskite Films

TL;DR

This study directly measures long-range carrier transport in oriented perovskite films using scanning photocurrent microscopy, revealing electron diffusion lengths around 10 micrometers, which explains high solar cell efficiencies.

Contribution

It introduces a method to directly measure long-distance carrier transport in perovskite films, providing new insights into their diffusion lengths and transport properties.

Findings

Electron diffusion length ~10 μm in perovskite films

Long-range carrier transport confirmed in highly oriented films

Method can distinguish diffusion lengths across different perovskite types

Abstract

Organometal halide perovskite has emerged as a promising material for solar cells and optoelectronics. Although the long diffusion length of photo-generated carriers is believed to be a critical factor responsible for the material's high efficiency in solar cells, a direct study of carrier transport over long distances in organometal halide perovskites is still lacking. We fabricated highly oriented crystalline CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) thin film lateral transport devices with long channel length (~ 120 $\mu$m). By performing spatially scanned photocurrent imaging measurements with local illumination, we directly show that the perovskite films prepared here have very long transport lengths for photo-generated carriers, with a minority carrier (electron) diffusion length on the order of 10 $\mu$m. Our approach of applying scanning photocurrent microscopy to organometal halide perovskites may be further used to elucidate the carrier transport processes and vastly different carrier diffusion lengths (~ 100 nm to 100 $\mu$m) in different types of organometal halide perovskites.