Ultrafast Photoexcitation Induced Nonthermal Lattice Expansion in 2D Perovskite

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.