Cocrystal Engineering: toward Solution‐Processed Near‐Infrared 2D Organic Cocrystals for Broadband Photodetection

Two-dimensional (2D) cocrystals open a new way to get 2D functional materials via crystal engineering instead of molecular engineering. Here, large-area 2D cocrystals with length reaching several millimeters with strong near-infrared (NIR) absorption have been successfully designed and prepared. Driven by the intermolecular charge-transfer (CT) interactions, zinc tetraphenylporphyrin (donor) and C 60 (acceptor) self-assemble into a NIR cocrystals with absorption wavelength up to 1080 nm. By tailoring the growth solvents and processes, the cocrystal morphologies can be tuned from 1D nanowires, 2D nanosheets to large-area 2D cocrystal films with length reaching several millimeters. Impressively, due to the highly ordered donor-acceptor arrangement, the CT absorption in the 2D cocrystals is significantly enhanced and becomes comparable to singlet absorption. The uniform 2D cocrystals, with enhanced CT absorption in the NIR region, displays a high responsivity of 2424 mA/W to NIR light and a fast response time of 0.6 s. The excellent device performance can be attributed to the generation of long-lived free charge carriers as revealed by transient absorption spectroscopy and the optimization of device configuration. This work shows an example of controlled growth of 2D cocrystals for broadband photodetectors, which reveals the brilliant future of cocrystal films for high-performance electronics and paves their way towards large-scale, integrated, flexible, practical applications.