Microwave-engineered, defect-regulated HEA-rGO heterointerfaces for broadband solar photothermal conversion

Efficient solar photothermal conversion requires broadband light absorption and rapid nonradiative energy dissipation. Here, we report a microwave-assisted strategy to simultaneously deoxygenate graphene oxide, reconstruct defect states, and induce in situ formation of AlCoCrFeNi high-entropy alloy nanoparticles on reduced graphene oxide, forming strongly coupled HEA–rGO heterointerfaces. Time-resolved structural analysis identifies a narrow kinetic window of 15–20 s at 900 W, where oxygen removal, sp²-network restoration, HEA nucleation, and interfacial anchoring occur concurrently. Spectroscopic analyses show that microwave treatment reconstructs rather than simply removes defects, transforming oxygen-associated localized states into partially delocalized electronic states coupled with the π-conjugated carbon network and HEA–rGO interfaces. This electronic rearrangement lowers the apparent optical transition energy from 1.58 eV for pristine GO to 0.86–0.92 eV for the microwave-treated HEA–rGO samples while retaining substantial defect-related states. Consequently, the optimized HEA–rGO composite shows enhanced and flattened absorption across 300–800 nm, suppressed radiative recombination, faster heating rates, and higher steady-state temperatures under 1–3 sun irradiation. Machine-learning-assisted descriptor analysis and first-principles calculations further reveal coupled defect-tail-state regulation, interfacial charge redistribution, near-Fermi-level state enrichment, and d–p orbital coupling. This work establishes a processing–structure–electronic-state–performance relationship for microwave-engineered HEA–rGO photothermal composites.