Femtosecond Laser Breaks the Lattice Symmetry and Induces Broadband Second Harmonic Generation in 3D Halide Perovskites

Abstract

3D halide perovskites have shown exceptional promise not only in photovoltaic and optoelectronic applications but also in nonlinear optics such as second harmonic generation (SHG). However, their efficiency in SHG is limited by the centrosymmetric nature of their crystal structures, and thus achieving SHG from 3D perovskites by breaking their inversion symmetry remains a formidable challenge. In this work, the precision and versatility of the femtosecond (fs) pulse laser writing technique are leveraged to fabricate microstructures of hybrid and inorganic perovskites with non‐centrosymmetric. These microstructures exhibit a strong SHG signal across a broad wavelength range (790–1210 nm), while the pristine 3D perovskites do not show any SHG. The enhanced SHG response is attributed to the laser‐induced modifications of the A‐site cations (MA, Cs) and halide defects in the pristine 3D perovskites, which disrupt the inversion symmetry. Furthermore, the potential of using non‐centrosymmetric microstructures of perovskites for ultrafast pulse characterization via the Frequency‐Resolved Optical Gating technique is demonstrated. These findings highlight the precise control of non‐centrosymmetric states using fs lasers, paving the way for the design and utilization of perovskites in advanced nonlinear optical and photonic applications.