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

Abstract

The organic photothermal materials provides a valid way to convert solar energy directly into thermal energy with non-pollution, safety and adaptability.However, the limitations of narrow absorption spectra, low molar absorption coefficients in the NIR region, and insufficient nonradiative decay, impair photothermal conversion efficiency (PCE) and hamper their potential applications. Herein, we present an effective strategy of "simultaneous donor engineering and boroncomplexation" to enhance photothermal conversion capability. Specifically, following the optimization of donor from phenyl-, thienyl-to triphenylamine (TPA) and modulating aggregated architecture through boron-complexation, six donor-acceptortype molecules (Ph-H, Ph-BF 2 , Th-H, Th-BF 2 , TPA-H and TPA-BF 2 ) were designed and synthesized. The single-crystal structures of TPA-H and TPA-BF 2 unveiled the regulatory principle of the coordination structure on aggregates and packing modes.The loose and zigzag arrangement of TPA-H dimers turned into the tight molecular packing of TPA-BF 2 dimers, facilitating the improvement of PCE by simultaneous broadening absorption spectra, high molar absorption coefficients in UV-vis-NIR region, and sufficient nonradiative decay. It is demonstrated that the PCE can be effectively tuned from 8.4% (Ph-BF 2 ) to 26.4% (TPA-BF 2 ). As a consequence, upon under 1 sun (1.0 kW cm -2 ) exposure, the water evaporation rate, solar-to-vapor efficiency and voltage output of TPA-BF 2 are improved to 1.43, 1.44, and 1.45 times to those of Ph-BF 2 . Among them, TPA-BF 2 enabled outstanding water evaporation rate of 1.321 kg m⁻² h⁻¹, a high solar-to-vapor efficiency of 90.5%, and high-voltage output (198 mV) in solar thermoelectric generator under 1 sun irradiation. The practical purification ability of seawater was also investigated. This study provides a guideline for the rational design of high-performance organic photothermal materials.