Researchers at the Technical University of Munich, the Max Planck Institute for Solid State Research, and the University of Stuttgart have developed a revolutionary material that can store energy from sunlight and release it as electricity for an extended period, even after sunset. This material, a two-dimensional covalent organic framework (COF) based on naphthalenediimide, acts as a solar reservoir, combining the functions of a solar cell and a battery into a single, lightweight, and sustainable system.
The COF framework absorbs sunlight and stabilizes the resulting photo-induced charges, enabling energy storage for more than 48 hours in aqueous environments. The stored charges can be actively discharged to power an external load, making it possible to supply electricity in the dark. The material’s performance exceeds that of many existing optoionic materials, and it does so without relying on metals or rare elements.
The researchers found that water plays a central role in stabilizing the stored charges, creating an energetic barrier that prevents recombination of the light-generated trapped charges. The material exhibits a charge storage capacity of 38 mAh/g, outperforming similar frameworks and other light-responsive materials. The theoretical mechanism behind this behavior was elucidated through extensive simulations, which evaluated various charge stabilization scenarios.
The team demonstrated excellent cycling stability, with over 90% capacity retention after multiple charging cycles, pointing to a powerful new platform for solar batteries. The innovative approach to solar batteries is being further researched at the recently founded MPG-TUM Solar Battery Center (SolBat). The researchers believe that this work highlights the potential of organic frameworks to be fine-tuned for advanced energy applications, using only organic building blocks and water.
The simplicity and robustness of the system are key to its success, with the material storing light-induced charges in a stable state, resulting from the unique interplay of molecular design, framework architecture, and environment. The researchers are excited about the potential of this material to provide sustainable, materials-driven energy storage solutions and off-grid applications. The development of this material marks a significant step towards creating a more sustainable and renewable energy future.