Comparative Analysis of Recombination Dynamics in Perovskite Solar Cells via Steady-State and Transient Photoluminescence

Quantifying recombination in halide perovskites is essential for controlling and enhancing the performance of perovskite solar cells. Here, we present a comprehensive analysis of recombination dynamics in perovskite solar cells, focusing on the impact of transient measurement techniques on assessing steady-state performance. We emphasize that the decay times extracted from transient photoluminescence measurements cannot generally be reduced to a single value but rather depend strongly on the charge carrier concentration. It follows that the magnitude of the decay time is reliant on the sensitivity of the measurement. We show photoluminescence decay curves with a large dynamic range of more than 10 orders of magnitude that demonstrate decay times from tens of nanoseconds up to hundreds of microseconds in perovskite films. Assuming these high decay times correspond to a recombination lifetime in steady state, one would expect a material with perfect photoluminescence quantum yield, which does however not coincide with the experimental findings. Instead, the decay times in transient measurements are prolonged by capacitive effects resulting from charge trapping and detrapping. We quantitatively explain both the transient and steady-state photoluminescence with the presence of a high density of shallow traps without the influence of deep traps. The same characteristic of increasing decay times remains in the full device, indicating capacitive effects from either shallow traps or transport layers and electrodes. With the help of voltage-dependent steady-state photoluminescence measurements we extract the recombination lifetimes during steady-state operation of the device and compare these to the transient decay times. Furthermore, this experiment allows for the determination of the voltage-dependent collection efficiency which illustrates collection losses up to 10% due to recombination even at short circuit. In summary, this study offers a deeper understanding of recombination dynamics in halide perovskite solar cells through the analysis of transient and steady-state measurements. Our findings underscore the importance of considering the influence of shallow traps and transport layers in interpreting decay times and optimizing device performance.