Self‐Assembly Morphology Manipulation by Side‐chain Engineering of Quinoxaline‐Substituted Organic Photothermal Molecules for Efficient Solar‐Thermal Conversion and Application

Organic photothermal materials have attracted more and more attention due to the structural diversity, flexibility, and compatibility. However, the energy conversion efficiency is limited due to the narrow absorption spectrum, strong reflection/transmittance and insufficient non‐radiative decay. Herein, we synthesized two quinoxaline‐based D‐A‐D‐A‐D type molecules with ethyl (BQE) or carboxylate (BQC) substitutes. The strong intramolecular charge transfer endow both molecules broad absorption ranging from 350–1000 nm. Besides, the high reorganization energy and weak molecular packing of BQE yield efficient non‐radiative decay. More importantly, the self‐assembly of BQE leads to textured surface and enhances the light‐trapping efficiency with dramatically reduced light reflection/transmittance. Consequently, BQE achieved impressive solar‐thermal conversion efficiency of 18.16% under 1.0 kW m−2 irradiation with good photobleaching resistance. Inspired by this, the water evaporation rate attained to 1.2 kg m−2 h−1 with efficiency of 83% for BQE based interfacial evaporation device under 1.0 kW m−2 simulated sunlight. Eventually, synergetic integration of solar‐steam and thermoelectric co‐generation device based on BQE is realized without sacrificing solar‐steam efficiency significantly, highlighting the practical application toward impactful photothermal exploitation. This work provides new insights of molecular design for enhancing light‐trapping management by molecular self‐assembly, which paves the way of photothermal‐driven application of organic photothermal materials.