Interpreting the Time-Resolved Photoluminescence of Quasi-2D Perovskites

Optical excitation of quasi-2D perovskites leads to excited-state populations of excitons, free charge carriers, or a mixture of both, depending on the type and amount of 2D spacer used. The fluence dependence of three quantities: 1) the time-resolved photoluminescence decay, 2) the photoluminescence quantum yield (PLQY) after pulsed excitation, and 3) the initial rate of photon emission, allow the mixture of excited states present to be determined. These can be described by a simple model considering noninteracting populations of excitons and charge carriers in separate subvolumes of the film. The model reproduces all unique features of the data, such as the anomalous peak of the PLQY at intermediate fluences, due to bimolecular free carrier emission gaining efficiency before exciton–exciton annihilation reduces the exciton emission efficiency. The excited state population varies from 100% excitons in films made from high concentrations of butylamine spacers to ≈7% excitons and 93% free carriers for low concentrations of 1-naphthylmethylamine spacers. The effective rates of free carrier recombination and exciton–exciton annihilation are high, often on the order of 1 × 10−9 cm3 s−1. ... mehrThe implications for the different excited-state populations and their dynamics in terms of device engineering are discussed.