A narrow-bandgap photothermal material based on a donor–acceptor structure for the solar–thermal conversion application

Abstract

Organic photothermal materials can effectively convert solar energy into thermal energy in an environmentally friendly manner and have great potential for applications such as desalination and thermoelectric power generation. However, some organic photothermal materials have low photothermal conversion efficiency and a narrow range of solar absorption, limiting the improvement of photothermal performance. In this contribution, to achieve a lower energy gap and high photothermal conversion efficiency, a strong acceptor benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole) (BBT) and the electron donor thiophene unit were introduced to synthesize a donor–acceptor (D–A) type organic conjugated molecule 4,8-bis(3-(2-ethylhexyl)-[2,2′-bithiophen]-5-yl)benzo[1,2-c:4,5-c′]bis([1,2,5]thiadiazole) (2TP-BBT). The atoms of C, N and S in BBT are essentially coplanar, attributed to the N atoms with higher electronegativity and CN groups with a lower-energy π-orbital, and benzothiadiazole exhibits strong electron-withdrawing properties. The 2TP-BBT solid shows a broad absorption spectrum ranging from 300 to 1400 nm. The 2TP-BBT solid has a high photothermal conversion efficiency of 22.38% under 1.0 kW m⁻² simulated solar irradiation, and under laser irradiation at 980 nm, the solid photothermal conversion efficiency of the 2TP-BBT molecule reached 43.32%. Additionally, the 2TP-BBT/non-woven fabric is applied in solar-driven water evaporation with a water evaporation rate up to 1.35 kg m⁻² h⁻¹ under 1.0 kW m⁻² simulated solar irradiation and a vapour conversion efficiency of 94.3%, which show superior water evaporation performance. The waste heat generated during solar water evaporation can be effectively used for synergistic thermoelectric power generation. This study demonstrates the application of photothermal D–A organic molecules in water purification and water–electric cogeneration application, therefore providing a valuable prospect of utilization in efficient solar thermal energy conversion.