# Ultrafast Photoexcitation Induced Nonthermal Lattice Expansion in 2D Perovskite

## TL;DR

Ultrafast photoexcitation in 2D perovskites causes non-thermal lattice expansion, improving photovoltaic performance and stability.

## Contribution

The study reveals a non-thermal lattice expansion mechanism in 2D perovskites triggered by ultrafast photoexcitation.

## Key findings

- Photoexcitation leads to non-thermal lattice expansion and increased bandgap in 2D DJ perovskites.
- The process enhances crystallinity, charge transport, and carrier lifetime, improving photovoltaic performance.
- The self-passivation mechanism reduces trap states and non-radiative recombination.

## Abstract

Light‐induced lattice change of perovskites is found to be critical for device performance. However, the underlying mechanism is still not fully understood. Here, real‐time time‐dependent density functional theory (rt‐TDDFT) calculations along with experiments are utilized to discern the photo‐induced electronic and structural changes in 2D Dion‐Jacobson (DJ) perovskites, showing that photoexcitation drives the non‐thermal lattice expansion, leading to the increase in bandgap. The ultrafast photoexcitation effect is found to improve the film crystallinity and charge transport, which brings a longer carrier lifetime and slower carrier recombination rate, leading to remarkable improvement of photovoltaic performance. These results not only provide insights into the photo‐physics of perovskites, but also show the potential of a new passivation technique for perovskite optoelectronics via ultrafast photoexcitation.

Photo‐induced lattice expansion in 2D Dion‐Jacobson (DJ) perovskites is a non‐thermal process, resulting in the more relaxed local lattice strain and the larger bandgap. It activates a self‐passivation mechanism, effectively diminishing trap state density. The synergy of these effects leads to suppressed non‐radiative recombination and prolonged charge carrier lifetimes, culminating in enhanced photovoltaic efficiency and stability.