Distinguishing Electron Diffusion and Extraction in Methylammonium Lead Iodide

Charge diffusion and extraction are crucial steps in the operation of solar cells. Here we show that time-resolved photoluminescence can be used to study electron diffusion in hybrid perovskite films and subsequent transfer to the adjacent electron extraction layer. As diffusion and transfer to the extraction layer are consecutive processes, they can be hard to distinguish, but by exciting from each side of the sample we can separate them and identify which process limits charge extraction. We find that the introduction of a fullerene monolayer between the methylammonium lead iodide (MAPbI3) and the electron-transporting SnO2 layers greatly increases the electron transfer velocity between them to the extent that electron diffusion limits the rate of electron extraction. Our results suggest that increasing the electron diffusion coefficient in MAPbI3 would further enhance the electron extraction rate, which could result in more efficient n-i-p type solar cells.

Automated summary

Charge diffusion and extraction are important processes in solar cells. In this study, time-resolved photoluminescence was used to investigate electron diffusion and transfer in hybrid perovskite films. It was found that introducing a fullerene monolayer between the MAPbI3 and SnO2 layers significantly increased the electron transfer velocity, suggesting that electron diffusion limits the rate of charge extraction. These findings suggest that enhancing the electron diffusion coefficient in MAPbI3 could improve the efficiency of solar cells.