Recent progress in nonlinear optics of 2D organic-inorganic hybrid perovskites （Invited）

Since the advent of perovskite materials, the numerous organic-inorganic hybrid perovskites have thrived vigorously over the decades. Two-dimensional (2D) organic-inorganic hybrid perovskites containing prototypical inorganic octahedron frames and diverse organic cations feature characteristics of intrinsic quantum-well structures and intriguing optoelectronic properties, and have therefore attracted research attention intensively for their optical applications in light emitting, sensing, modulation, photovoltaic cells and telecommunication devices. The low-cost and solution-processed fabrications as well as the alternative organic spacer cations endue 2D hybrid perovskites with flexible layer distances, number of layers, and variable lattice distortion, leading to effectuate the adjustable frameworks as well as higher tunability in optical and photonic applications. In particular, they also demonstrate distinguished and appealing nonlinear optical (NLO) characters whether in the second-order, third-order NLOs or the higher-order NLOs such as second-harmonic generation (SHG), terahertz generation, two-photon absorption (2PA), and saturable absorption (SA), three-photon absorption (3PA), etc., under the excitation of laser pulses. Here, we discuss on the construction of the various 2D hybrid perovskites with different structural features. Furthermore, some representative properties and applications of these 2D hybrid perovskites are discussed in both linear and nonlinear optical regimes. Lastly, the status quo and challenge of 2D hybrid perovskites are elevated, and the future developments of 2D hybrid perovskites is prospected.