Solar
energy and ambient heat are two inexhaustible energy sources for addressing the
global challenge of energy and sustainability. Solar thermal battery based on molecular
switches that can store solar energy and release it as heat has recently attracted
great interest, but its development is severely limited by both low energy
density and short storage stability. On the other hand, the efficient recovery
and upgrading of low-grade heat, especially that of the ambient heat, has been
a great challenge. Here we report that solar energy and ambient heat can be
simultaneously harvested and stored, which is enabled by room-temperature
photochemical crystal-to-liquid transitions of small-molecule photoswitches.
The two forms of energy are released together to produce high-temperature heat during
the reverse photochemical phase change. This strategy, combined with molecular
design, provides high energy density of 320-370 J/g and long-term storage
stability (half-life of about 3 months). On this basis, we fabricate
high-performance, flexible film devices of solar thermal battery, which can be
readily recharged at room temperature with good cycling ability, show fast rate
of heat release, and produce high-temperature heat that is >20<sup> o</sup>C
higher than the ambient temperature. Our work opens up a new avenue to harvest ambient
heat, and demonstrate a feasible strategy to develop high-performance solar
thermal battery.
