Excitonic Enhancement and Excited Excitonic States in CsPbBr3 Halide Perovskite Single Crystals

Abstract

Halide perovskites are novel photonics materials promising numerous applications in fields such as photovoltaics, LED light sources, microlasers, and radiation detectors. Many halide perovskites are direct-gap semiconductors, and Wannier–Mott excitons play a significant role in their optical properties near the fundamental absorption edge. The high oscillator strength of these states favors applications where efficient interaction with light is required. In this work, to study excitonic states in CsPbBr3 halide perovskite single crystals, the reflection spectroscopy at temperatures from 4 K was used. A reflection coefficient up to 70% was observed for the n=1 exciton state, followed by weak excited states of excitons with n=2 and n=3. It should be noted that the Sommerfeld enhancement factor should be considered for a correct description of the behavior of the dielectric constant, taking into account excitonic effects.

Low-Temperature Refractive Index Dispersion in MAPbI3 Halide Perovskite Single Crystal

“…The spectrum is dominated by the resonance of a free exciton at 1.638 eV. This spectrum can be described in the model of a semi-infinite layer of uncoupled oscillators 26 or with higher precision in the model of excitonic polaritons. 21 Red curve in Figure 1a shows the reflection from the microcrystal serving as a microcavity.…”

Free Exciton and Defect-Related States in CH3NH3PbCl3 Perovskite Single Crystal

“…(a) PL (green) and reflectivity (blue) spectra captured at temperature T = 4 K and fit of reflectivity (dashed red) by the uncoupled oscillators model . (b) Photos of the same MAPbCl 3 single crystal in different projections on millimeter paper.…”

Robust Free Excitons in CH3NH3PbI3Halide Perovskite Revealed by Four‐Wave Mixing

“…[19] The oscillator strength of the exciton resonance in these materials greatly exceeds that in traditional covalent semiconductors. [20,21] An exceptional feature of halide perovskites is their defect tolerance, [22,23] which can be formulated as the fact that the most common impurities and defects do not create deep traps inside the bandgap. This leads to a significant increase in the robustness of excitons compared to traditional semiconductors: the excitonic emission is observed in photoluminescence (PL) even in highly defective polycrystalline thin films of halide perovskites.…”

“…[ 19 ] The oscillator strength of the exciton resonance in these materials greatly exceeds that in traditional covalent semiconductors. [ 20,21 ]…”