Circularly polarized light (CPL)-sensitive direct detection, which is able to distinguish the handedness of chiral light, has attracted extensive attention. However, current CPL-sensitive direct detection mainly focuses on a single mode. The visible–near-infrared (Vis–NIR) dual-modal detection, which is important for improving device sensitivity and night-vision performance, remains to be explored.

Two-photon absorption (TPA) characterized by simultaneous absorption of a pair of photons shows possibilities in Vis-NIR dual modal photodetection. Two-dimensional (2D) hybrid chiral perovskites combining excellent semiconducting properties, intrinsic chirality and superior TPA effect derived from the strong light-matter interaction of the multi-quantum-well structure present themselves as promising candidates for Vis-NIR dual modal CPL-sensitive direct detection.

In a study published in J. Am. Chem. Soc., the research group led by Prof. LUO Junhua from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences reported the first realization of Vis-NIR dual modal CPL-sensitive direct detection in a 2D chiral perovskite, (R-BPEA)₂PbI₄ (R-BPEA = (R)-1-(4-Bromophenyl)ethylammonium). 

The researchers unveiled the chiral optical properties of (R-BPEA)₂PbI₄ using the circular dichroism (CD) measurements. The CD and absorption spectra indicated that (R-BPEA)₂PbI₄ exhibits CD signals before the band edge cutoff (552 nm), and the maximum anisotropy of CD is 0.003 (at 476 nm). 

They then evaluated the two-photon absorption (TPA) coefficient of (R-BPEA)₂PbI₄ using the static intensity-dependent transmission measurement. The results indicated that (R-BPEA)₂PbI₄ shows a TPA coefficient of up to 55 cm/MW, benefiting from strong light–matter interaction of the layered structure. This value almost falls around the highest value of 2D hybrid perovskites. The TPA properties were further verified by power dependent photoluminescence upon 800 nm.  

Through temperature cooling process, the researchers obtained the bulk single crystals of 2D chiral perovskite (R-BPEA)₂PbI₄ with size up to 4 X 4X 2 mm³. 

Furthermore, they revealed the Vis-NIR dual modal CPL-sensitive direct photodetection of (R-BPEA)₂PbI₄ using the bulk-crystal-based lateral architecture devices. Using a 520 nm laser diode and a femtosecond pulsed laser system as the light sources, they found that under both visible light and near infrared light, (R-BPEA)₂PbI₄ exhibits superior CPL-sensitive direct photodetection properties with on/off ratios of higher than 10³, and anisotropy factors of higher than 0.1.

This study demonstrates that introducing TPA effect is an efficacious strategy for achieving high performance Vis-NIR dual modal CPL-sensitive direct photodetection.