Second harmonic generation in iodine quasi-2D halide perovskite crystals

Layered quasi-two-dimensional halide perovskites have attracted significant attention as exceptional materials for nonlinear optics and photonics applications due to their remarkable photophysical properties. The incorporation of quasi-2D spacer ligands into the halide perovskite framework induces alterations in the crystal structure and leads to changing its properties due to quantum confinement effects. Notably, certain crystal structures may exhibit a lack of center symmetry, facilitating the observation of second harmonic generation. Furthermore, the optical properties of halide perovskite crystals can vary dramatically based on the composition of the quasi-2D spacers. In this study, we investigate the second harmonic generation signal of two compositions: PEA2MAPb2I7 and a novel methyl-substituted PEA derivative, MePEA2MAPb2I7. Our results reveal distinct second-harmonic generation characteristics for both compositions and demonstrate enhanced stability in MePEA-based crystals. This work contributes to the understanding of the relationship between crystal composition and nonlinear optical behavior in quasi-2D perovskites, paving the way for future advancements in photonic applications.