Power-law photoluminescence decays in perovskites

Lead-halide perovskites exhibit power-law decay rather than exponential decay at long delay times.Consequently, to quantify the recombination, the determination of a constant lifetime is no longer a feasible approach; instead, a bimolecular recombination coefficient can be determined, which correlates with the photoluminescence quantum efficiency.

Power-law photoluminescence decays in perovskites

Transient photoluminescence (tr-PL) spectroscopy is the most widely used technique for characterizing the recombination in halide perovskite films, layer stacks, and devices. So far, the recorded tr-PL decay has often been analyzed using exponential or multi-exponential fitting, and the charge-carrier lifetimes have been extracted. However, tr-PL decays exponentially only in the limiting case, where the decay is dominated by recombination via a midgap defect. In the presence of radiative recombination, shallow defects, and diffusion effects, recombination decays nonexponentially, and the decay often resembles a power law between the photoluminescence intensity and time. We observed power-law decay for a variety of lead-halide perovskite compositions measured at a sufficiently high fluence as well as over a sufficient dynamic range, which suggests that the extracted decay time changes depending on the charge-carrier concentration and delay time. Thus, the single lifetime values determined from tr-PL decays are rarely suitable for providing a quantitative measure of recombination. Instead, we propose that the use of effective bimolecular recombination coefficients can be a viable solution to simplify the data analysis and enable quantitative comparison. We verified that the photoluminescence quantum yields exhibit a clear inverse relationship with the bimolecular recombination coefficients, indicating that the bimolecular recombination coefficient is a good figure of merit for charge-carrier recombination in lead-halide perovskites. Furthermore, to avoid misinterpretation of the transient photoluminescence data, the impact of the repetition rate and background subtraction methods was investigated experimentally and numerically. Finally, we briefly summarize the workflow for transient photoluminescence measurement and data analysis, focusing on linking the experimental data to an interpretation based on physical models in a direct way.

Further information can be found here:
https://doi.org/10.1002/aenm.202403279

Last Modified: 24.09.2024