Chemists at the University of California, Santa Barbara have developed a new material capable of capturing and storing solar energy as heat, providing an alternative to traditional batteries and electrical grids. The findings were published in the journal Science by Associate Professor Grace Han and her research team.
The new material is a modified organic molecule known as pyrimidone. It absorbs sunlight, stores the energy within its chemical bonds, and releases it as heat when needed. This process is part of an emerging field called Molecular Solar Thermal (MOST) energy storage.
“The concept is reusable and recyclable,” said Han Nguyen, a doctoral student in the Han Group and lead author of the paper.
Nguyen compared the system to photochromic sunglasses: “Think of photochromic sunglasses. When you’re inside, they’re just clear lenses. You walk out into the sun, and they darken on their own. Come back inside, and the lenses become clear again,” Nguyen continued. “That kind of reversible change is what we’re interested in. Only instead of changing color, we want to use the same idea to store energy, release it when we need it, and then reuse the material over and over.”
The design for this molecule was inspired by DNA structures that can undergo reversible changes under ultraviolet light. By creating a synthetic version with computational modeling support from UCLA’s Ken Houk, the researchers ensured stability so that stored energy would not dissipate over years.
“We prioritized a lightweight, compact molecule design,” Nguyen said. “For this project, we cut everything we didn’t need. Anything that was unnecessary, we removed to make the molecule as compact as possible.”
Unlike conventional solar panels that convert light into electricity or other systems that convert light into chemical energy for storage elsewhere, this molecule directly stores sunlight as potential heat energy within itself—much like a mechanical spring under tension.
“We typically describe it as a rechargeable solar battery,” Nguyen said. “It stores sunlight, and it can be recharged.”
The new molecule has an energy density exceeding 1.6 megajoules per kilogram—about twice that of standard lithium-ion batteries—and surpasses previous optical switch technologies in capacity.
A significant achievement highlighted in their study was using stored heat from the material to boil water under ambient conditions—a result rarely achieved before in this area.
“Boiling water is an energy-intensive process,” Nguyen said. “The fact that we can boil water under ambient conditions is a big achievement.”
This technology could be used for applications such as off-grid heating during camping trips or residential water heating solutions. Because pyrimidone dissolves in water easily, it could be integrated into rooftop solar collectors to absorb sunlight during daylight hours before being stored for later use.
“With solar panels, you need an additional battery system to store the energy,” said co-author Benjamin Baker, also a doctoral student at UCSB’s Han Lab. “With molecular solar thermal energy storage, the material itself is able to store that energy from sunlight.”
The project received support through the Moore Inventor Fellowship awarded to Grace Han in 2025 for her work developing these “rechargeable sun batteries.”
