Self-assembling nanoparticles could help scale solar energy harvesters

It has a high absorbance and low emissivity and does not need nanofabrication.
Ameya Paleja
Thermal collector
Thermal collector


A collaborative effort from researchers at universities in China and Singapore has resulted in the production of a solar harvester that not only uses nanoparticles but can also assemble by itself. The technology could help harvest solar energy in an environmentally friendly way and help solve the fossil fuel crisis, a press release said.

Solar thermal technology is an upcoming method of harvesting the sun's energy which converts the incident light into thermal energy. The major challenge in its adoption is the dissipation of energy while also maintaining high absorption. Current methods of energy harvesting rely on micro or nano-engineering.

Solar energy is transferred as an electromagnetic wave within a broad frequency range. “A good solar-thermal harvester should be able to absorb the wave and get hot, thereby converting solar energy into thermal energy," said Ying Li of Zhejiang University, who was involved in the research. "The process requires a high absorbance (100 percent 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 do so, current methods design a harvester with a periodic nanophotonic structure. The rigidity of the pattern and high fabrication costs, though, have led to the flexibility and scalability of these modules.

Self-assembling nanoparticles

The research collaboration designed a device that uses a quasiperiodic nanoscale pattern. In this pattern, the molecules are largely arranged in an alternating and consistent pattern, while some regions contain random defects. These defects, however, do not have an impact on the performance of the harvester. Instead, since the design requirements are not that strict, it provides an advantage when it comes to scalability.

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The fabrication process uses self-assembling iron oxide (Fe3O4) nanoparticles which can interact with nearby particles to organize into the material structure without any external instruction.

Self-assembling nanoparticles could help scale solar energy harvesters
The device’s solar-thermal conversion (left) and solar thermoelectric harvesting (right).

The quasiperiodic nanophotonic structure demonstrated a high absorbance (greater than 94 percent) under normal solar illumination with highly suppressed emissivity (less than 0.2). These features enabled the absorber to demonstrate a fast and significant temperature rise greater than 176 Fahrenheit (80 degrees Celsius).

This thermal energy harvested by the device can also be converted into electricity using thermoelectric materials. The researchers built a flexible planar solar thermoelectric harvester using the nanoparticles that reached a sustaining voltage of over 20 millivolts per square centimeter. This energy would be sufficient to power 20 LEDs per square meter of solar irradiation, the press release said.

"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,” Li added.

The research findings were published today in the journal APL Photonics.

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