1D Diisopropylammonium Lead Iodide Perovskite Shows Exceptional Optical Stability and Third‐Order Nonlinearity

Abstract Low‐dimensional lead‐halide perovskites show wide structural and compositional diversity. Multiple functionalities can be introduced in these materials for diverse linear and nonlinear optical applications. Nonlinear optical (NLO) processes depend on material polarizability, crystal symmetry, and processibility. The flexibility of choosing organic cations in lead‐halide perovskites provides an opportunity for enhanced NLO responses by enhancing the overall system polarizability. A highly polarizable diisopropylammonium [Dipa; ((CH₃)₂CH)₂NH₂⁺] is used as an A‐site cation to synthesize one‐dimensional (1D) lead‐iodide (DipaPbI₃) perovskite single crystals and the third‐harmonic generation (THG) in the excitation wavelength range of 1200–1600 nm is explored. DipaPbI₃ single crystals exhibit exceptionally efficient resonance‐enhanced THG, amazing optical stability, and a high polarization ratio due to enhanced bulk‐polarization. The THG efficiency (χ⁽³⁾ ≈ 4 × 10⁻¹⁸ m² V⁻²) and laser‐induced damage threshold (LIDT, 144 GW cm⁻²) are an order of magnitude higher than the reported perovskites explored as THG materials. Density functional theory calculations show a significantly higher polarizability for Dipa cation, asserting the influence of the cation polarizability on the NLO efficiency of the perovskite. The stability of these single crystals in ambient conditions for an extended period adds to their potential for commercial application in the near future.