Multiphoton Absorption Coefficients of Organic–Inorganic Lead Halide Perovskites CH₃NH₃PbX₃ (X = Cl, Br, I) Single Crystals

Hybrid organic–inorganic lead halide perovskites have recorded unprecedented improvement in efficiency as fourth-generation photovoltaic materials. Recently, they have attracted enormous interest in nonlinear optics stemming basically from their excellent optoelectronic properties. Here, we investigate multiphoton absorption (MPA) in high-quality MAPbX₃ (MA = CH₃NH₃ and X = Cl, Br, I) bulk single crystals synthesized by an inverse-temperature crystallization (ITC) method. The two-photon absorption (2PA) coefficients under picosecond pulse excitation are determined to be β = 23 ± 2 cm/GW and 9 ± 1 cm/GW for MAPbI₃ and MAPbBr₃ at λ = 1064 nm, and 13 ± 2 cm/GW for MAPbCl₃ at λ = 532 nm. The 2PA coefficients are comparable to those of conventional semiconductors having similar bandgaps and can be explained by a two-band model. Furthermore, we characterize the three-photon absorption behavior of MAPbCl₃ at λ = 1064 nm, yielding γ = 0.05 ± 0.01 cm³/GW². The polarization dependence of MPA is also probed to experimentally estimate the degree of anisotropy. The hybrid perovskites are promising materials for nonlinear optical applications due to polarization-dependent MPA response and subsequent strong photoluminescence emission, especially for the Br- and I-containing compounds