Pressure-Induced Emergence of Visible Luminescence in Lead Free Halide Perovskite Cs<sub>3</sub>Bi<sub>2</sub>Br<sub>9</sub>: Effect of Structural Distortion
Debabrata Samanta, Pinku Saha, Bishnupada Ghosh, Sonu Pratap Chaudhary, Sayan Bhattacharyya, Swastika Chatterjee, Goutam Dev Mukherjee
Abstract
We report a detailed high pressure study involving X-ray diffraction, Raman spectroscopy, and photoluminescence measurements on a model Pb-free solar cell material Cs3Bi2Br9 halide perovskite. The sample starts showing photoluminescence in a broad range of 550–900 nm above 1.4 GPa, due to an isostructural transition to a distorted unit cell. Further enhancement in intensity with pressure is found to be driven by an increase in distortion of BiBr6 octahedra. Electronic band structure calculations show the sample in the high pressure phase to be an indirect band gap semiconductor. The photoluminescence peak shows a kink at higher energy and a broad asymmetric peak at lower energies due to the recombination of free excitons and self-trapped excitons, respectively. The blue shift of the PL peaks until about 4.4 GPa can be related to the extensive structural distortion before the transition to lowest symmetry triclinic phase.