Hydrostatic Pressure Driven Band Gap Tuning and Self-Trapped Exciton Formation in (4FPEA)$_2$SnBr$_{4}$ Halide Perovskite

TL;DR

This study investigates how hydrostatic pressure influences exciton behavior and band gap tuning in layered tin halide perovskites, revealing pressure-induced shifts and the formation of self-trapped excitons with implications for optoelectronic applications.

Contribution

It provides new insights into pressure effects on exciton dynamics and self-trapped exciton formation in 2D tin halide perovskites, highlighting the role of lattice rigidity and dielectric screening.

Findings

NBE excitons redshift linearly under pressure at room temperature.

Self-trapped excitons show an anomalous blueshift under pressure.

Lattice rigidity influences the stabilization of self-trapped excitons.

Abstract

Two-dimensional tin halide perovskites provide a highly tunable platform for exciton phonon coupling and local lattice distortions, enabled by their intrinsically soft lattice. We report a combined temperature and pressure dependent photoluminescence study of the layered perovskite (4FPEA)$_{2}$SnBr$_{4}$. At room temperature, its optical response is dominated by near band edge (NBE) excitons, which redshift linearly under hydrostatic pressure up to $\sim$3 GPa, indicating a rigid band edge behavior without phase transitions. Cooling reveals a broad, strongly Stokes shifted self-trapped exciton (STE) emission, evidencing a crossover from delocalized to self localized excitonic states. Strikingly, while NBE emission redshifts under pressure, STE emission exhibits an anomalous blueshift, reflecting pressure induced modification of the exciton phonon energy landscape. In contrast, the iodide analogue (4FPEA)$_{2}$SnI$_{4}$ shows no STE emission under identical conditions, highlighting the critical role of lattice rigidity and dielectric screening in stabilizing self-trapped excitons.