External Stimuli Triggered Structural Dynamics and Phase Change in 2D Perovskite Materials

2D Metal halide perovskites are emerging light emitters for bright light emitting diodes and lasing media. The soft structures can undergo dynamic changes under external stimuli such as light, heat and electrical field. In this work, we investigate the lattice dynamics and order to disorder transition in 2D perovskite thin films. First, we used time-resolved X-ray scattering technique to probe the lattice dynamics upon laser trigger. We observed a significant lattice expansion after laser pulse, and the expansion extended over 10s of nano seconds. We attributed the expansion to the rotation of the organic molecules that sustain the expanded states. Next, we investigated the phase stability of the 2D perovskites under laser irradiation, heat stress and electrical field stress. We observed an order to disordered structural transition, where the multiple n-numbered 2D phase can be re-distributed with the stress. In conclusion, despite the promising emission properties of 2D perovskites, their phase instability possesses a potential challenge in building stable LEDs or lasers. The dynamic nature of the 2D perovskites introduces internal stress that can lead to phase degradation that can impact the operational stability.