Narrow-Bandgap Donor-Acceptor Polymers for Efficient Solar Water Evaporation and Thermoelectric Power Generation

Organic photothermal materials have garnered significant interest due to their structural diversity, tunability, and favorable compatibility. However, their narrow absorption spectra often restrict further enhancement of energy conversion efficiency. In this work, we designed and synthesized two donor-acceptor (D-A) alternating copolymers, TTQT and TTQP. The polymer TTQT incorporates benzo[2,1-b:3,4-b']dithiophene as the A unit, whereas TTQP employs a phenanthrene-substituted [1,2,5]thiadiazolo[3,4-g]quinoxaline unit. Both polymers feature thieno[3,2-b]thiophene as the D unit, linked via thiophene π bridge. The D-A alternating structure promotes an extended conjugation plane along the polymer backbone and facilitates strong intramolecular charge transfer, resulting in a narrowed bandgap and notable far-infrared absorption. Under one sun illumination, TTQP and TTQT achieve solar-thermal conversion efficiencies of 21.3% and 28.4%, respectively. An interfacial evaporator fabricated with TTQT demonstrates an energy conversion efficiency of 86.5%. Moreover, by coupling the TTQT-based solar evaporator with a thermoelectric module, an integrated photothermal-thermoelectric system capable of concurrent steam and electricity generation without sacrificing solar evaporation performance was assembled. This work provides a novel strategy for the design of organic polymer photothermal materials by optimizing the structure of the quinoxaline unit, and offers feasible material support for the realization of photothermally driven water-electricity integrated systems.