Solid-State Norbornadiene Photothermal Films for Efficient Solar Energy Storage

Abstract

A solid-state photothermal (PT) energy storage film based on norbornadiene (NBD) molecules has been developed, which converts solar energy into chemical energy through photoisomerization reactions and releases it as thermal energy upon heating. The optical absorption, energy storage properties, tensile strength, and thermal conductivity of the four NBD molecules are evaluated. Among them, the NBD4 film demonstrates the highest thermal storage capacity, reaching up to 202 J g⁻¹. In addition, the influence mechanism of different substituents and polystyrene (PS) concentrations on NBD is analyzed from a microscopic perspective. When integrated with photovoltaic (PV) cells, the solid-state PT energy storage films absorb UV light, lowering the PV cell temperature ≈5 °C while simultaneously storing UV photons as chemical energy. This results in ≈3% increase in overall system efficiency. After irradiation, the NBD film is additionally integrated with the thermoelectric generator (TEG). The stored energy is converted into electrical energy, enhancing thermoelectric conversion efficiency. The solid-state film proposed in this study effectively addresses the issues of poor thermal stability and leakage associated with liquid-based systems while remaining fully compatible with existing PV modules, thereby enhancing solar energy storage and heat release efficiency.