Halide mixing inhibits exciton transport in two-dimensional perovskites despite phase purity

TL;DR

This study reveals that mixing halides in phase-pure 2D perovskites hampers exciton transport due to local energy landscape disorder, even without phase segregation, impacting optoelectronic device performance.

Contribution

It demonstrates that halide mixing affects exciton transport in phase-pure 2D perovskites, highlighting intrinsic disorder as a key factor.

Findings

Halide mixing reduces exciton diffusivity in phase-pure 2D perovskites.

Bromide-rich perovskites are especially sensitive to iodide addition.

Simulations attribute transport inhibition to energetic disorder from alloying site randomness.

Abstract

Metal-halide perovskites are a versatile material platform for light-harvesting and light-emitting applications as their variable chemical composition allows the optoelectronic properties to be tailored to specific applications. Halide mixing is one of the most powerful techniques to tune the optical bandgap of metal-halide perovskites across wide spectral ranges. However, halide mixing has commonly been observed to result in phase segregation, which reduces excited-state transport and limits device performance. While the current emphasis lies on the development of strategies to prevent phase segregation, it remains unclear how halide mixing may affect excited-state transport even if phase purity is maintained. In this work, we study excitonic excited-state transport in phase pure mixed-halide 2D perovskites. Using transient photoluminescence microscopy, we show that, despite phase purity, halide mixing inhibits exciton transport in these materials. We find a significant reduction even for relatively low alloying concentrations, with bromide-rich perovskites being particularly sensitive to the introduction of iodide ions. Performing Brownian dynamics simulations, we are able to reproduce our experimental results and attribute the decrease in diffusivity to the energetically disordered potential landscape that arises due to the intrinsic random distribution of alloying sites. Our results suggest that even in the absence of phase segregation, halide mixing may still impact carrier transport due to the local intrinsic inhomogeneities in the energy landscape.