Researchers from China transformed balsa wood into an engineered material capable of capturing sunlight, storing 175 kilojoules per kilogram in the form of heat, achieving 91.27% photothermal efficiency, and even generating up to 0.65 volts even after sunset
Researchers from China transformed balsa wood into a multifunctional material capable of absorbing sunlight, storing it as heat, and generating electricity even after sunset. The proposal, detailed in an article published in the journal Advanced Energy Materials, seeks to overcome a limitation of solar energy: the interruption of generation when light disappears and the low efficiency in storing collected energy.
The solution was developed by internally re-engineering the wood at multiple scales, from nano to micro, to create a structure capable of capturing heat and later releasing it for energy use. When this stored heat is transferred to a thermoelectric device, the system can also produce electricity.
Wood redesigned to capture and store energy
The starting point was the removal of natural lignin from the wood, a substance that acts as a glue and holds the fibers together. With this, the researchers obtained a porous structure formed by tiny open channels inside the material.
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These channels were coated with ultrathin sheets of black phosphorene, a material that absorbs sunlight at various wavelengths and converts it into heat. Since phosphorene degrades quickly in air, the team applied a protective layer composed of tannic acid and iron ions.
In the next step, silver nanoparticles were added to enhance the sunlight absorption capacity. Then, the researchers included a water-repellent layer to keep the wood dry and more resistant to deterioration in different weather conditions.
Internal structure accelerates heat conduction
After preparing the balsa wood structure, the scientists filled the material with stearic acid, a bio-based wax used to store heat. This material melts when heated, stores energy, and upon cooling, solidifies and releases the accumulated heat.
One of the factors explaining the system’s thermal performance is the path taken by heat within the material. Instead of spreading across the surface, it propagates along the fibers, which accelerates the movement of energy towards an external generator.
This arrangement allows stored heat to be utilized more quickly for conversion into electricity. Thus, the modified wood simultaneously acts as a light collector, thermal energy storage, and support for subsequent electrical generation.
Tests show high photothermal efficiency
In tests conducted in a solar simulator, the material achieved a photothermal efficiency of 91.27%. This means that almost all incident light was converted into usable heat.
Furthermore, the material stored 175 kilojoules of energy per kilogram. When connected to a thermoelectric generator, the modified balsa wood-based system produced up to 0.65 volts.
Resistance to fire, bacteria, and fungi
The tests also evaluated the coating’s behavior against common risks in outdoor structures. The performance was considered positive against fire, bacteria, and fungi.
In the study, the authors reported that the hybrid coating reduced the heat release rate by 27.4% and the total heat release rate by 31.2%. The material also showed good performance against E. coli and S. aureus.
By combining light capture, thermal storage, electrical generation, and protection against deterioration, the team presented a platform described as scalable and environmentally friendly. With this configuration, wood is now used as a basis for advanced utilization of solar thermal energy even after sunset.

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