Stable biexcitons in two-dimensional metal-halide perovskites with strong dynamic lattice disorder

TL;DR

This study reveals that single-layer 2D hybrid perovskites exhibit stable biexcitons with high binding energies at room temperature, emphasizing the significance of multi-exciton effects despite lattice disorder.

Contribution

The paper provides the first measurement of biexciton binding energy in 2D perovskites using coherent spectroscopy, highlighting strong multi-exciton correlations in these materials.

Findings

Biexciton binding energy is approximately 44 meV at room temperature.

Binding energy increases by about 25% when cooled to 5 K.

Strong multi-exciton effects are present despite lattice disorder.

Abstract

With strongly bound and stable excitons at room temperature, single-layer, two-dimensional organic-inorganic hybrid perovskites are viable semiconductors for light-emitting quantum optoelectronics applications. In such a technological context, it is imperative to comprehensively explore all the factors --- chemical, electronic and structural --- that govern strong multi-exciton correlations. Here, by means of two-dimensional coherent spectroscopy, we examine excitonic many-body effects in pure, single-layer (PEA)$_2$PbI$_4$ (PEA = phenylethylammonium). We determine the binding energy of biexcitons --- correlated two-electron, two-hole quasiparticles --- to be $44 \pm 5$\,meV at room temperature. The extraordinarily high values are similar to those reported in other strongly excitonic two-dimensional materials such as transition-metal dichalchogenides. Importantly, we show that this binding energy increases by $\sim25$\% upon cooling to 5\,K. Our work highlights the importance of multi-exciton correlations in this class of technologically promising, solution-processable materials, in spite of the strong effects of lattice fluctuations and dynamic disorder.