Solar Thermal Storage and Room-Temperature Fast Release Using a Uniform Flexible Azobenzene-Grafted Polynorborene Film Enhanced by Stretching

Deformation-controlled solar thermal storage and release are important for thermal management of dynamic systems. However, few researchers have examined cyclic solid-state solar thermal utilization with different deformations. A uniform flexible stretchable solar thermal fuel film is presented using polynorbornene-templated azobenzene (PNB-Azo) with ring-opening metathesis polymerization and covalent grafting. This film has a high degree of isomerization and good storage stability compared to push–pull electronic interaction. At 20% strain rate, the film combines high-degree photocharging (85%), high energy density (49.0 Wh kg –1 ), and high rate of heat release induced by blue light (475 nm) at room temperature. Greater free volume improves isomerization and the first-order kinetic constant is increased by 1 order of magnitude. Reversible electric-driven dynamic stretching during charging and discharging enables PNB-Azo“fingers” to release heat more rapidly than static stretched film, resulting in a temperature increase of 1.5 °C. The result indicates that PNB-Azofilm can be used as a high-power dynamic solar heat source by controlling the deformation.