Boosting photothermal conversion through a simultaneous donor engineering and boron complexation strategy for solar-driven applications

Abstract

Organic photothermal materials facilitate the direct conversion of solar energy into thermal energy via a method that is safe and adaptable and generates no pollution. However, their limitations, including narrow absorption spectra, low molar absorption coefficients in the NIR region, and insufficient nonradiative decay, impair the photothermal conversion efficiency (PCE) and hamper their potential applications. Herein, we present an effective strategy, “simultaneous donor engineering and boron complexation”, to enhance the photothermal conversion capability. Specifically, following the optimization of the donor from phenyl- to thienyl- and to triphenyl-amine (TPA) and modulating the aggregated architecture through boron complexation, six donor–acceptor-type molecules (Ph-H, Ph-BF₂, Th-H, Th-BF₂, TPA-H and TPA-BF₂) were designed and synthesized. The single-crystal structures of TPA-H and TPA-BF₂ unveiled the regulatory effect of the coordination structure on their aggregates and packing modes. The loose and zigzag arrangement of the TPA-H dimers turned into the tight molecular packing of the TPA-BF₂ dimers, facilitating an improvement in PCE by simultaneously broadening their absorption spectra, increasing their molar absorption coefficients in the UV-vis-NIR region, and enhancing nonradiative decay. It is demonstrated that the PCE can be effectively tuned from 8.4% (Ph-BF₂) to 26.4% (TPA-BF₂). As a consequence, under 1 sun (1.0 kW m⁻²) exposure, the water evaporation rate, solar-to-vapor efficiency and voltage output of TPA-BF₂ improved by 1.43, 1.44, and 1.45 times those of Ph-BF₂, respectively. Among them, TPA-BF₂ exhibited an outstanding water evaporation rate of 1.321 kg m⁻² h⁻¹, a high solar-to-vapor efficiency of 90.5%, and a high voltage output (198 mV) in a solar thermoelectric generator under 1 sun irradiation. The practical purification ability of seawater was also investigated. This study provides guidelines for the rational design of high-performance organic photothermal materials.