Opto-electronic and kinetic properties of defect states in FA0.7Cs0.3Pb(I0.9Br0.1)3 thin films

TL;DR

This study investigates the defect states in FA0.7Cs0.3Pb(I0.9Br0.1)3 perovskite thin films using combined electrical and optical techniques, revealing their energetic distribution, mobility, and impact on material properties.

Contribution

It introduces a combined methodology using TAS, SSPC, and SSPG to characterize defect states in perovskite thin films, providing new insights into their energetic and kinetic properties.

Findings

Defects exhibit exponential band tail states from lattice disorder.

Presence of acceptor-like Gaussian distribution 0.21 eV below conduction band.

Room temperature mobility of dopants is approximately 0.5-1×10^{-7} cm^2 V^{-1} s^{-1}.

Abstract

Despite the remarkable success in increasing the efficiency and stability of perovskite solar cells over the last decade, the underlying defect landscape of halide perovskites remains unclear. Some charged defects in perovskites migrate in response to an applied electric field, which complicates their characterization with standard techniques. We combine thermal admittance spectroscopy (TAS) with lateral photoconductivity-based methods, such as the thermal steady-state photocurrent (SSPC) and the steady-state photocarrier grating (SSPG), to estimate the kinetic and electrical properties of defects in thin films of vacuum-deposited FA$_{0.7}$Cs$_{0.3}$Pb(I$_{0.9}$Br$_{0.1}$)$_3$ perovskite. The experimental results are consistent with exponential band tails states coming from the lattice disorder, an acceptor-like Gaussian distribution 0.21~eV below the conduction band and approximately equal concentrations of donors and acceptors ($1.7\times10^{17}$ cm$^{-3}$). One of the dopants has room temperature mobility of $(0.5{-}1)\times10^{-7}$ cm$^2$ V$^{-1}$ s$^{-1}$ with a thermal activation energy of 0.28--0.40 eV.