Toward strong nonlinear optical absorption properties of perovskite films via porphyrin axial passivation

Defects within perovskite layers are considered to be a primary factor that inhibits nonlinear optical (NLO) performance, and mitigating or eliminating them is indispensable for the implementation of high-performance perovskite-based photonic and energy devices. Herein, we propose a novel defect modulation strategy through binding the functional groups at the axial positions of porphyrins with the defects of perovskites. Two axially-coordinated porphyrin molecules (TiOPr and SnOHPr) were utilized as effective functional additives to passivate the defects and control perovskite crystallization, while the role of axial functional groups of porphyrins has been systematically studied. Z-scan measurement results demonstrate that porphyrin-treated perovskite films exhibit prominently enhanced optical absorption nonlinearities under ultrafast femtosecond (fs) laser excitation at 800 nm in comparison to the MAPbI₃ perovskite film, the NLO absorption coefficient (β) values for the modified films are approximately one or two orders of magnitudes superior to that of the pristine film. This significant improvement in NLO performance likely stems from the increased photoinduced ground-state dipole moment of the perovskite film treated by porphyrin during the process of two-photon absorption (TPA), and their photoinduced charge/energy transfer between perovskite and porphyrin. Particularly, the MAPbI₃/SnOHPr film displays the largest β values (636.92–6621.42 cm GW⁻¹) among all measured samples at different irradiation energies and a low optical limiting threshold of 5 mJ cm⁻², which may profit from the dual-functional passivation effect of SnOHPr onto perovskite, suggesting its great potential as optical limiters. These observations strongly indicate that porphyrin-axial passivated perovskite films are outstanding material candidates for optical limiting applications towards ultrafast fs laser pulses in the near-infrared region. Our work affords a feasible paradigm for constructing high-performance NLO perovskite materials through porphyrin-axial passivation of defects.