Abstract: Among perovskite semiconductors, quasi-two-dimensional (2D) materials are attractive for the pursuit of electrically driven lasing given their excellent performance in light-emitting diodes (LEDs) and their recent success in continuous-wave optically pumped lasing. We investigate the spontaneous photoluminescence emission and amplified spontaneous emission (ASE) of a series of quasi-2D emitters, and their directly analogous 3D materials formed by removing the 2D organic spacer by annealing. Although the PL photoluminescence (PL) (at low optical excitation power) from quasi-2D films with high 2D spacer fractions can be much brighter than that from their 3D counterparts, the ASE thresholds of these quasi-2D materials tend to be higher. This counter-intuitive behavior is investigated through time-resolved photophysical studies, which reveal the emission in the high-spacer-content quasi-2D perovskite can be exclusively excitonic, and the exciton–exciton annihilation of quasi-2D perovskite starts to take over the exciton dynamics at a low exciton density (<1016?cm−3). To lower ASE thresholds in quasi-2D materials it is necessary to increase the volume fraction of thick quantum wells, which we achieve by decreasing the spacer content or by utilizing 1-naphthylmethylamine (NMA) linkers. The increase of the volume fraction of thick quantum wells correlates with an increased contribution of free carrier recombination to the emission process of the quasi-2D materials. These results suggest that material development of quasi-2D materials for gain applications should target fast free charge carrier recombination rates by engineering the well thickness and size and not maximum photoluminescence quantum yields under low power excitation.

Exciton versus free carrier emission: Implications for photoluminescence efficiency and amplified spontaneous emission thresholds in quasi-2D and 3D perovskites
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DOI: 10.1016/j.mattod.2021.05.002