# Effect of Dimensionality on the Optical Absorption Properties of CsPbI$_3$ Perovskite Nanocrystals

## TL;DR

This study investigates how reducing the dimensionality of CsPbI$_3$ perovskite nanocrystals affects their optical absorption, revealing shifts in band-gap behavior, electron-phonon interactions, and defect-related features at cryogenic temperatures.

## Contribution

It provides a detailed analysis of the impact of nanocrystal dimensionality on optical properties, including band-gap shifts and defect states, supported by experimental measurements and modeling.

## Key findings

- Decreasing dimensionality reduces electron-phonon coupling.
- Quantum confinement causes homogeneous broadening of absorption lines.
- Defect states near the valence band-edge create absorption tails in nanocubes.

## Abstract

The band-gaps of CsPbI$_3$ perovskite nanocrystals are measured by absorption spectroscopy at cryogenic temperatures. Anomalous band-gap shifts are observed in CsPbI$_3$ nanocubes and nanoplatelets, which are modeled accurately by band-gap renormalization due to lattice vibrational modes. We find that decreasing dimensionality of the CsPbI$_3$ lattice in nanoplatelets greatly reduces electron-phonon coupling, and dominant out-of-plane quantum confinement results in a homogeneously broadened absorption lineshape down to cryogenic temperatures. An absorption tail forms at low-temperatures in CsPbI$_3$ nanocubes, which we attribute to shallow defect states positioned near the valence band-edge.