Controlling Exciton/Exciton Recombination in 2-D Perovskite Using Exciton-Polariton Coupling

In this paper, we demonstrate that exciton/exciton annihilation in the 2D perovskite (PEA)₂PbI₄ (PEPI)─a major loss mechanism in solar cells and light-emitting diodes, can be controlled through coupling of excitons with cavity polaritons. We study the excited state dynamics using time-resolved transient absorption spectroscopy and show that the system can be tuned through a strong coupling regime by varying the cavity width through the PEPI layer thickness. Remarkably, strong coupling occurs even when the cavity quality factor remains poor, providing easy optical access. We demonstrate that the observed derivative-like transient absorption spectra can be modeled using a time-dependent Rabi splitting that occurs because of transient bleaching of the excitonic states. When PEPI is strongly coupled to the cavity, the exciton/exciton annihilation rate is suppressed by 1 order of magnitude. A model that relies on the partly photonic character of polaritons explains the results as a function of detuning.