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Giant Nonlinear Optical Response in Triple Cation Halide Mixed Perovskite Films

The versatility of perovskites through chemical composition modification is critical for enhancing performance of a range of potential applications such as light emitters and integrated photovoltaics. However, a systematic study on the nonlinear optical (NLO) responses of these perovskites is still lacking. Here, for the first time, the NLO properties of triple cation mixed halide perovskite (TCMHP) films, (Cs0.06FA0.79MA0.15)Pb (I0.85Br0.15)3, using Z‐scan and time‐resolved spectroscopy, are investigated. It is found that TCMHP film shows strong saturable absorption at 395 nm, reverse saturable absorption such as two‐ and three‐photon absorption (2PA, 3PA) at 790 nm (near the bandgap), and 3PA at 1200 nm. The 3PA phenomena at 790 nm are attributed to the phonon‐assisted anti‐Stokes process. The 2PA and 3PA coefficients are estimated to be ≈2.1 cm MW−1 and ≈900 cm3 GW−2, respectively, which are an order of magnitude larger than those of MAPbI3 and other perovskites. Moreover, it is demonstrated that these giant 2PA and 3PA coefficients of TCMHP can be used to realize optical stabilization. The observed strong multiphoton absorption response will enable TCMHP materials to be suitable for various nonlinear optical applications such as multiphoton‐based imaging, optical modulator, and all‐optical switching devices.