Charge Carrier and Exciton Dynamics in Perovskites Revealed by Time-Integrated Photoluminescence after Double-Pulse Excitation

The rate constants that describe the decays of excited states (free charge carriers, excitons) are important parameters for perovskite materials. Typically, these rates are determined using detectors with high time-resolution to record the time-dependent photoluminescence on the nanosecond scale. Herein, a method is applied that uses two excitation pulses with a variable delay and an inexpensive detector capable of measuring only the quasisteady state photoluminescence. Based on how the time-integrated photoluminescence varies as a function of the delay time between the two excitation pulses, the rate constants for exciton-exciton annihilation, monomolecular exciton decay, bimolecular free charge carrier recombination, and monomolecular trapping of free charge carriers can be extracted. To demonstrate the method quasi-2D perovskites are investigated as they are known to exhibit excited-state populations that can be exciton dominated, free charge carrier dominated, or a mixture of the two. The method leads to unique curves and accurate extracted parameters in all cases. The introduced method of determining excited-state lifetimes can be used with detectors that only have a low temporal resolution. This opens the path to the spatial mapping of excited-state dynamics using standard cameras which would be attractive for quality control of photovoltaic layers.