Large-Area Flexible Organic Charge-Transfer Cocrystal Membranes for Photothermal and Photothermoelectric Conversion with Excellent Durability

Organic photothermal materials with superior capabilities in green and sustainable energy conversion have attracted significant attention due to their simple processability, flexibility, and good biocompatibility. Nevertheless, their practical applications are limited by complex synthesis and difficulties in forming large-area films. Here, we report a photothermal charge-transfer cocrystal composed of benzo[c]carbazole (BCZ) and tetracyanoquinodimethane (TCNQ), self-assembled via a simple solution-evaporation method. This cocrystal achieves a high photothermal conversion efficiency (PCE) of ∼71% under 808 nm irradiation. Furthermore, large-area BCZ-TCNQ membranes can be conformally coated onto various substrates using a bar-coating technique, serving as flexible heat sources with excellent durability. By integrating the organic cocrystal with thermoelectric devices under 1 sun irradiation, the photothermoelectric system produces an excellent output voltage of 0.22 V and a power density of 5.5 W m–2. This work demonstrates the potential of organic cocrystals for outdoor power generation through solar-thermal-electric energy conversion.