These images show the solar-thermal conversion (left) and solar thermoelectric harvesting (right) conducted by the novel solar harvester. Image: Zifu Xu.
These images show the solar-thermal conversion (left) and solar thermoelectric harvesting (right) conducted by the novel solar harvester. Image: Zifu Xu.

Solar-thermal technology is a promising, environmentally friendly energy-harvesting method with a potential role to play in solving the fossil fuel energy crisis.

The technology transforms sunlight into thermal energy, but suppressing energy dissipation while maintaining high absorption has proved challenging. Existing solar-energy harvesters that rely on micro- or nanoengineering don’t have sufficient scalability and flexibility, and so a novel strategy is required for efficiently capturing solar light while simultaneously simplifying the fabrication process and reducing costs.

Now, in a paper in APL Photonics, researchers from Harbin University, Zhejiang University and Changchun Institute of Optics, all in China, and the National University of Singapore report their design for a novel solar harvester with enhanced energy conversion capabilities.

“Solar energy is transferred as an electromagnetic wave within a broad frequency range,” explained Ying Li from Zhejiang University. “A good solar-thermal harvester should be able to absorb the wave and get hot, thereby converting solar energy into thermal energy. The process requires a high absorbance (100% is perfect), and a solar harvester should also suppress its thermal radiation to preserve the thermal energy, which requires a low thermal emissivity (zero means no radiation).”

To achieve these goals, a solar harvester usually comprises a system with a periodic nanophotonic structure. But the flexibility and scalability of these modules can be limited due to the rigidity of the pattern and high fabrication costs.

In contrast, the researchers designed a solar harvester that employs a quasiperiodic nanoscale pattern – meaning most of it comprises an alternating and consistent pattern, while the remaining portion contains random defects that do not affect the performance. It turns out that loosening the strict requirements on the periodicity of the pattern significantly increases the device’s scalability.

The fabrication process makes use of self-assembling nanoparticles, which form an organized material structure based on their interactions with nearby particles without any external instructions. The thermal energy harvested by the device can then be transformed into electricity using thermoelectric materials.

“Unlike previous strategies, our quasiperiodic nanophotonic structure is self-assembled by iron oxide (Fe3O4) nanoparticles, rather than cumbersome and costly nanofabrication,” said Li.

Their quasiperiodic nanophotonic structure can achieve high absorbance (greater than 94%) with suppressed thermal emissivity (less than 0.2). This means that, under natural solar illumination, the absorber can experience a fast and significant temperature rise (greater than 80°C).

Based on the absorber, the team built a flexible planar solar thermoelectric harvester. This was able to produce a significant sustaining voltage of over 20 millivolts per square centimeter, allowing it to power 20 light-emitting diodes per square meter of solar irradiation. This strategy could serve low-power-density applications for more flexible and scalable engineering of solar-energy harvesting.

“We hope our quasiperiodic nanophotonic structure will inspire other work,” said Li. “This highly versatile structure and our fundamental research can be used to explore the upper limit of solar-energy harvesting, such as flexible scalable solar thermoelectric generators, which can serve as an assistant solar harvesting component to increase the total efficiency of photovoltaic architectures.”

This story is adapted from material from the American Institute of Physics, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.