Superior Photo-carrier Diffusion Dynamics in Organic-inorganic Hybrid Perovskites Revealed by Spatiotemporal Conductivity Imaging

TL;DR

This study uses spatiotemporal conductivity imaging to reveal that organic-inorganic hybrid perovskites exhibit long diffusion lengths for electrons and holes due to a balance of their lifetimes and mobilities, explaining their high solar cell efficiency.

Contribution

It provides direct, spatially resolved measurements of carrier dynamics in hybrid perovskites, highlighting the interplay of carrier lifetimes and mobilities in diffusion behavior.

Findings

Electrons and holes have microsecond-scale lifetimes.

Long diffusion lengths of 3-5 micrometers for both carriers.

Carrier mobility differences compensate for lifetime disparities.

Abstract

The outstanding performance of organic-inorganic metal trihalide solar cells benefits from the exceptional photo-physical properties of both electrons and holes in the material. Here, we directly probe the free-carrier dynamics in Cs-doped FAPbI3 thin films by spatiotemporal photoconductivity imaging. Using charge transport layers to selectively quench one type of carriers, we show that the two relaxation times on the order of 1 microsecond and 10 microseconds correspond to the lifetimes of electrons and holes in FACsPbI3, respectively. Strikingly, the diffusion mapping indicates that the difference in electron/hole lifetimes is largely compensated by their disparate mobility. Consequently, the long diffusion lengths (3 ~ 5 micrometers) of both carriers are comparable to each other, a feature closely related to the unique charge trapping and de-trapping processes in hybrid trihalide perovskites. Our results unveil the origin of superior diffusion dynamics in this material, crucially important for solar-cell applications.