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Recently, there have been intensive and extensive research works on perovskites because of their excellent electrical and optical properties. This review is focused on their multiphoton absorption (MPA) and applications. All the MPA coefficients or cross‐sections reported in the literature are summarized. Many experimental data show that the MPA strengths of nanoscale perovskites are several orders of magnitude greater than their bulk counterparts. The second‐ and third‐order quantum perturbation theories predict that, while the two‐band transitions play a significant role in 3D crystals of perovskites, the exciton‐light interactions dominate in the case of 2D perovskites. Other influencing factors on the MPA magnitudes are also discussed. Their potential applications are also highlighted in laser‐frequency upconversion and sub‐bandgap photodetection. [ABSTRACT FROM AUTHOR]

Multiphoton absorption may find many technological applications, such as enhancing the conversion efficiency of solar cells by the utilization of sub‐band‐energy photons, below‐bandgap photodetection through the simultaneous absorption of several infrared photons for photocurrent generation, or light frequency upconversion for high‐resolution, 3D imaging. To enhance multiphoton absorption in semiconducting materials, one of the strategies is to explore low‐dimensional excitons. Here, a quantum perturbation theory on a giant enhancement in three‐photon absorption (3PA) arising from 2D excitons in multilayered crystals of organic–inorganic hybrid perovskites is presented. The maximal 3PA coefficient is predicted to be in the range of 2–7 cm3 GW−2 at 1100 nm, the largest values reported so far for any 2D and bulk semiconductors at room temperature. Excellent agreement between theory and the experimental findings unambiguously demonstrates a pivotal role in the enhancement of 3PA played by 2D excitons. The theory predicts that the resonant 3PA coefficient should be enhanced further by at least two orders of magnitude with very low temperature. The findings are essential for understanding giant 3PA arising from 2D excitons in layered hybrid perovskites and may open new pathways for highly efficient conversion from infrared light energy to either electrical energy or higher‐frequency light emission/lasing. Here, a giant enhancement in three‐photon absorption (3PA) arising from two‐dimensional (2D) excitons is theoretically predicted and experimentally observed in multi‐layered crystals of organic–inorganic hybrid perovskites. This finding is essential for understanding 3PA in layered hybrid perovskites and may open new pathways for highly‐efficient conversion from infrared light energy to either electrical energy or higher‐frequency light emission/lasing. [ABSTRACT FROM AUTHOR]