Lead halide perovskites provide a test bed for exploring nonlinear optical properties. Although the underlying centrosymmetric crystal structure of 3D lead halide perovskites precludes the phenomenon of second harmonic generation, the third and higher-order harmonic generation are allowed. The third harmonic generation (THG) from CsPbBr₃ NCs with Ruddlesden–Popper planar faults (RP-CsPbBr₃), formed via post-synthetic fusion-growth is enhanced with an effective third-order susceptibility of the order of 10^–18 m² V^–2 .

The application of an electric field is an effective mechanism for breaking the symmetry in otherwise symmetric molecular or other systems. Electric-field induced second harmonic generation (EFISHG) provides a tool for investigating chromophore orientation in nonlinear optical materials and understanding transport at the semiconductor-dielectric interface in thin film transistors.