Effective Steady-State Recombination Decay Times in Comparison to Time-Resolved Photoluminescence Decay Times in Halide Perovskite Solar Cells

Abstract

One of the key topics in perovskite solar cells is the reduction of charge carrier recombination, with the aim of increasing power conversion efficiency. The recombination lifetime is a commonly used tool, as it directly affects the current–voltage curve via the diffusion length. The lifetime is often estimated using time-domain measurement methods such as time-resolved photoluminescence. However, two obstacles emerge when applying the transiently measured decay times to the steady-state theory. In general, the decay time depends on the charge carrier concentration, and it is often not clear under which conditions the transient measurement must be conducted to be comparable with the steady-state performance of the device. Furthermore, diffusion and capacitive effects due to charge injection and extraction can influence transient techniques and cause the measured decay time to deviate from the sought-after recombination lifetime. Voltage-dependent steady-state photoluminescence measurements can be used to estimate the internal voltage during device operation and allow the extraction of collection efficiencies and effective steady-state decay times that are independent of transport and capacitive effects. Here, the differences between the steady-state and transient decay times are identified and discussed, and the losses in the current–voltage curve caused by extraction issues are quantified.