Breakthrough in organic photothermal crystals powers next-gen solar thermoelectrics

Breakthrough in organic photothermal crystals powers next-gen solar thermoelectrics
by Simon Mansfield
Sydney, Australia (SPX) Apr 23, 2025

Researchers at Soochow University have achieved a major milestone in solar thermoelectric generator (STEG) technology, introducing an innovative organic radical photothermal cocrystal that significantly boosts efficiency in converting solar heat to electricity. The development could accelerate applications in wearable electronics, IoT devices, and thermally adaptive systems.

To improve STEG performance, scientists have explored diverse materials capable of maximizing photothermal conversion. Traditional candidates include carbon derivatives, metal oxides, and phase-change substances. However, the introduction of a new organic charge-transfer (CT) cocrystal marks a leap forward in material design. The cocrystal, composed of the electron acceptor 2,6-dibromonaphthalene-1,4,5,8-tetracarboxylic dianhydride (Br2NDA) and coronene (COR), delivers a record-breaking photothermal conversion efficiency (PCE) of 67.2% under near-infrared irradiation.

Engineered through a straightforward solution self-assembly process, the COR-Br2NDA (CBC) cocrystal forms crystalline microrods with high structural order. A suite of analytic techniques confirmed strong CT interaction between the donor and acceptor molecules. UV-Vis spectroscopy revealed an absorption range from 350 to 1100 nm with a redshift signaling enhanced charge transfer. Photoluminescence studies showed near-total quenching, indicating efficient nonradiative heat generation.

Additional structural and spectroscopic analyses, including ESR and solid-state NMR, confirmed the ground-state electron delocalization and thermal durability of the material. When irradiated with an 808 nm laser at 0.367 W cm-2, the CBC sample quickly reached 86oC, outperforming many conventional photothermal materials. Notably, its temperature response remained stable over repeated cycles.

To apply this photothermal material, the team embedded CBC crystals into a transparent resin to produce a functional ink. This ink was used to coat a thermoelectric generator, forming a composite solar thermoelectric device. Under simulated solar exposure equivalent to two suns, the coated generator reached 70.3oC and produced an output voltage of 209 mV - a 375% increase compared to an uncoated device.

Beyond power generation, the CBC-TEG composite also exhibited a dynamic response to modulated infrared light. By adjusting laser power and pulse duration, the device successfully encoded and transmitted Morse code signals. This demonstrates the system's potential not only in energy harvesting but also in secure, contactless communication.

This research lays a foundation for the scalable development of radical-activable photothermal cocrystals. It also introduces a dual-function platform for both high-efficiency solar-thermal conversion and intelligent signal processing, potentially impacting fields ranging from advanced electronics to energy-autonomous sensors.

Research Report:Radical-Activable Charge-Transfer Cocrystals for Solar Thermoelectric Generator toward Information Conversion