Record Second‐Harmonic Generation in a Lead‐Free 2D Hybrid Halide Perovskite

Abstract Hybrid halide perovskites (HHPs) have garnered significant attention among researchers exploring nonlinear optical (NLO) materials due to their robust structural designability and impressive photophysical characteristics. Despite considerable efforts in optimizing their chemical compositions and structural dimensions, the role of large distorted [AgX 6 ] 5− octahedra in double perovskites on the design of HHPs materials with strong second harmonic generation (SHG) effect is underestimated or even overlooked. In the study, a double perovskite structure (DFPD) 4 AgBiBr 8 ·H 2 O (DFPD = 3,3‐difluoropiperidinium), is obtained with significant polar distortion of [AgBr 6 ] 5− octahedra, which shows a remarkable SHG intensity of 13.0 × KDP, a moderate birefringence of 0.095@532 nm, a high laser‐induced damage threshold (LIDT) value of 241.3 MW cm −2 , and an ultra‐long structural stability (>12 months) at 60% relative humidity air atmosphere. The research underscores the advantages of utilizing double perovskites with highly distorted [AgBr 6 ] 5− octahedra in the development of HHPs with excellent SHG response, and provides a novel insight into the design of advanced NLO materials.