Unraveling the defect landscape of wide-bandgap perovskites from electrical and photoelectrical characterization of thin films and solar cells

Abstract

Understanding and controlling defect states in halide perovskites is critical to advancing their performance in solar cells, yet their complex defect landscape remains elusive. Charged defects in perovskites can migrate under an applied electric field, complicating their characterization by conventional approaches. Here, we integrate current-voltage (IV) and thermal admittance spectroscopy (TAS) with lateral photocurrent methods, including thermal steady-state photocurrent (SSPC) and steady-state photocarrier grating (SSPG), to probe 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 interpreted with advanced numerical simulations to account not only for the energy positions of defects in the bandgap but also for their mobilities. The low activation energies observed in the capacitance steps rule out free-carrier trapping and emission as their origin, pointing instead to charged-defect (or ionic) migration. We estimate the free-carrier mobilities and the defect distribution inside the bandgap, along with their capture coefficients. Our results reveal exponential bandtail states arising from dynamic lattice disorder and identify a Gaussian-like defect distribution 0.21~eV from the band edge, which dominates recombination. Donors and acceptors are present at nearly equal concentrations ($\sim 2 \times 10^{18}$~cm$^{-3}$). The mobile species responsible for the capacitance steps is one of the dopants, exhibiting an average mobility of $10^{-8}$~cm$^2$~V$^{-1}$~s$^{-1}$ at 300~K with a thermal activation energy of around 0.34~eV.