Pressure induced emission enhancement and bandgap narrowing: experimental investigations and first principles theoretical simulations on a model halide perovskite

TL;DR

This study combines experimental high-pressure measurements and first-principles simulations to investigate how pressure affects emission and bandgap properties in a lead-free halide perovskite, revealing phase transitions and electronic structure changes.

Contribution

It provides new insights into pressure-induced electronic and structural transitions in Cs3Sb2Br9 through combined experimental and theoretical approaches.

Findings

Electronic transition at 3 GPa with Raman anomalies

Bandgap reduction of 27.5% predicted by DFT

Structural transition from trigonal to monoclinic at 8 GPa

Abstract

We report high-pressure photoluminescence, Raman scattering, and x-ray diffraction measurements on a lead-free halide perovskite $Cs_3Sb_2Br_9$. At about 3 GPa, an electronic transition manifests itself through a broad minimum in linewidth, a maximum in the intensity of $E_g$, $A_{1g}$ Raman modes, and the unusual change in the $c/a$ ratio of the trigonal lattice. The large compressibility and observed Raman anomalies indicate to a soft material with strong electron-phonon coupling. The observed below bandgap broadband emission in the photoluminescence measurement indicates the recombination of self-trapped excitons. The initial blueshift of the photoluminescence peak reinforces itself to the redshift at around 3 GPa due to the change in the electronic landscape. A first order trigonal to a monoclinic structural transition is also seen at 8 GPa. The first-principles density functional theory (DFT) calculations reveal that the electronic transition is associated with direct-to-indirect bandgap transition due to changes in the hybridization of $Sb-5s$ and $Br-4p$ orbitals near the Fermi level in the valence band. The experimentally observed Raman modes are assigned to their symmetry using the density functional perturbation theory. In addition, the DFT calculations predict a 27.5\% reduction of the bandgap in the pressure range 0-8 GPa.