Tunable photostriction of halide perovskites through energy dependent photoexcitation

TL;DR

This study reveals how the photostriction in halide perovskites depends on excitation energy, showing contraction at low energies and expansion at high energies, explained through first-principles calculations and orbital analysis.

Contribution

It introduces a microscopic method to understand photostriction in insulators based on electronic band orbital characters, specifically applied to lead-halide perovskites.

Findings

Light induces lattice contraction at low excitation energies.

Giant lattice expansion occurs at high excitation energies.

Different valence states have opposing effects on bonding.

Abstract

Halide perovskites exhibit giant photostriction, that is, volume or shape changes upon illumination. However, the microscopic origin of this phenomenon remains unclear and there are experimental reports of both light-induced lattice expansion and contraction. In this paper we establish a general method, based on first-principles calculations and molecular orbital theory, which provides a microscopic picture of photostriction in insulators based on the orbital characters of their electronic bands near the Fermi level. For lead-halide perovskites, we find that different valence states have different bonding characters, leading to opposing strengthening or weakening of bonds depending on the photoexcitation energy. The overall trend is that light induces lattice contraction at low excitation energies, while giant lattice expansion occurs at high excitation energies, rationalizing experimental reports.