Resonant Degenerate Four-Wave Mixing at the Defect Energy Levels of 2D Organic-Inorganic Hybrid Perovskite Crystals

Synergistic Effect of Laser, Water Vapor, and Electron-Beam on the Degradation of Quasi-Two-Dimensional Ruddlesden-Popper Perovskite Flakes

Understanding the effects of laser light, water vapor, and energetic electron irradiation on the intrinsic properties of perovskites is important in the development of perovskite-based solar cells. Various phase transition and degradation processes have been reported when these agents interact with perovskites separately. However, detailed studies of their synergistic effects are still missing. In this work, the synergistic effect of three factors (exposure to laser light, water vapor, and e-beam) on the optical and physical properties of two-dimensional (2D) Ruddlesden-Popper (RP) perovskite flakes [(BA)2(MA)2Pb3Br10] has been investigated in an environmental cell. When the perovskite flakes were subjected to moderate laser irradiation in a humid environment after prior e-beam irradiation, the photoluminescence (PL) peak centered at 480 nm vanished, while a new PL peak centered at 525 nm emerged, grew, and then quenched. This indicates the degradation process of the 2D RP perovskite was a phase transition to a three-dimensional (3D) perovskite [MAPbBr3] followed by the degradation of 3D perovskite. The spatial distribution of the 525 nm PL signal shows that this phase-transition process spreads across the flake to the area as far as ∼40 μm from the laser spot. Without humidity, the phase transition happened in the laser-irritated area but did not spread, which suggests that moisture enhanced the ion migration from the laser-scanned area to the rest of the flake and accelerated the phase transition in the nearby area. Experiments with no prior e-beam irradiation show that e-beam irradiation is the key to activating the 2D-3D phase transition. Therefore, when the three factors work synergistically, a conversion from the 2D RP perovskite into the 3D perovskite is not localized and propagates through the perovskite. These findings contribute to our understanding of the complex interactions between external stimuli and perovskite materials, thereby advancing the development of efficient and stable perovskite-based solar cells.

Phase Transitions and Dynamics in Mixed Three- and Low-Dimensional Lead Halide Perovskites

Lead halide perovskites are extensively investigated as efficient solution-processable materials for photovoltaic applications. The greatest stability and performance of these compounds are achieved by mixing different ions at all three sites of the APbX3 structure. Despite the extensive use of mixed lead halide perovskites in photovoltaic devices, a detailed and systematic understanding of the mixing-induced effects on the structural and dynamic aspects of these materials is still lacking. The goal of this review is to summarize the current state of knowledge on mixing effects on the structural phase transitions, crystal symmetry, cation and lattice dynamics, and phase diagrams of three- and low-dimensional lead halide perovskites. This review analyzes different mixing recipes and ingredients providing a comprehensive picture of mixing effects and their relation to the attractive properties of these materials.