Anisotropic Organic Charge-Transfer Cocrystal-Based Near-Infrared Polarized Photodetectors

Polarization-sensitive photodetection in the second near-infrared (NIR-II) region is highly desirable for advanced optoelectronic and imaging applications. Organic semiconductors are attractive choices for polarized photodetectors for their intrinsically anisotropic optical responses arising from ordered molecular packing. However, most reported organic polarized photodetectors are restricted to wavelengths below 1000 nm, due to the absorption limitations of organic polarization-sensitive materials. Herein, we develop an organic single-crystalline charge-transfer (CT) cocrystal, BF₄NQ, by incorporating a highly electronegative acceptor to regulate intermolecular electronic coupling and crystal packing. Structural and photophysical studies indicate that the strong CT interaction not only enables NIR-II absorption but also contributes to highly anisotropic optical responses, facilitating polarization-sensitive photodetection. Benefiting from the synergistic effects of strong CT interaction and highly ordered crystal packing, BF₄NQ-based photodetectors exhibit outstanding polarization sensitivity with a photocurrent anisotropy ratio of 3.81 at 1064 nm and a high specific detectivity (D*) of 2.50 × 10¹⁴ Jones in the NIR-II window. This work extends the functionality of organic CT cocrystals from broadband NIR photodetection to polarization-sensitive NIR-II photodetection and highlights the potential of CT engineering for integrating narrow-bandgap photoresponse and polarization sensitivity within a single organic material.