# Carrier Diffusion in Thin-Film CH3NH3PbI3 Perovskite Measured using Four-Wave Mixing

## TL;DR

This study uses femtosecond four-wave mixing spectroscopy to measure carrier diffusion in perovskite thin films, revealing that carriers diffuse across multiple grains before recombination, aiding rapid transport property characterization.

## Contribution

It demonstrates a novel application of FWM spectroscopy for direct measurement of carrier diffusion and transport properties in perovskite thin films.

## Key findings

- Carrier diffusion coefficient measured via FWM.
- Carriers traverse multiple grain boundaries.
- FWM enables rapid transport characterization.

## Abstract

We report the application of femtosecond four-wave mixing (FWM) to the study of carrier transport in solution-processed CH3NH3PbI3. The diffusion coefficient was extracted through direct detection of the lateral diffusion of carriers utilizing the transient grating technique, coupled with simultaneous measurement of decay kinetics exploiting the versatility of the boxcar excitation beam geometry. The observation of exponential decay of the transient grating versus interpulse delay indicates diffusive transport with negligible trapping within the first nanosecond following excitation. The in-plane transport geometry in our experiments enabled the diffusion length to be compared directly with the grain size, indicating that carriers move across multiple grain boundaries prior to recombination. Our experiments illustrate the broad utility of FWM spectroscopy for rapid characterization of macroscopic film transport properties.