Using Nanotechnology to Make Solar Cells Cheaper and More Efficient

The US solar industry has seen advances in solar cell technology in recent years. In the race to make solar cells cheaper and more efficient, researchers are betting on new designs that exploit nanostructures—materials engineered on the scale of a billionth of a meter. Using nanotechnology, researchers can experiment with and control how a material generates, captures, transports and stores free electrons—properties that are important for the conversion of sunlight into electricity.

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Inexpensive thin-film cells are crucial to meet the need for cheap solar cells using nanotechnology. Thin film cells use a polycrystalline silicon layer 1-2 micrometers in thickness compared to the conventional, expensive crystalline silicon wafers with a thickness of 200-300 micrometers.

How Nanotechnology Improves Solar Cells

Using nanoparticles in solar cell production has several benefits such as reduction in manufacturing costs due to the low temperature process compared to the high temperature vacuum deposition used to make conventional solar cells. Lower installation costs can be achieved by using flexible thin films instead of rigid crystalline panels. Solar cells produced using quantum dot deposition have higher efficiency than conventional solar panels.

Nanotech Methods that Show Promise

Two nanotech methods have shown particular promise for engineering solar cell materials. One uses thin films of metal oxide nanoparticles, such as titanium dioxide, doped with other elements, such as nitrogen. Another strategy employs quantum dots (nano-size crystals) that strongly absorb visible light. These tiny semiconductors inject electrons into a metal oxide film, or "sensitize" it, to increase solar energy conversion. Both doping and quantum dot sensitization extend the visible light absorption of the metal oxide materials.

However, combining the first two approaches appears to yield better solar cell materials than either does alone. A thin film doped with nitrogen and sensitized with quantum dots performed better than the sum of its two individual components.

The hybrid material offered a number of advantages. Nitrogen doping allowed the material to absorb a broad range of light energy, including energy from the visible region of the electromagnetic spectrum. The quantum dots also enhanced visible light absorption and boosted the photocurrent and power conversion of the material.

Compared with materials doped only with nitrogen or only embedded with cadmium selenide quantum dots, the nanocomposite showed higher performance, as measured by the "incident photon to current conversion efficiency" (IPCE). The nanocomposite's IPCE was about three times greater than the sum of the IPCEs for the two other materials.

In addition to these processes, a method called Aerotaxy is also becoming popular to grow semiconducting nanowires on gold nanoparticles. Self assembly techniques can be used to align the nanowires on a substrate in order to form a solar cell. Another method uses a combination of silver nanocubes scattered over a thin layer of gold to lower losses due to reflection.

Nanocomposites’ Role in Other Energy Technologies

Nanocomposite materials could be used to not only enhance solar cells, but also in other energy industries. Combining a highly efficient solar cell with a state-of-the-art photoelectrochemical cell can result in a device that could, in theory, use energy generated from sunlight to split water and produce hydrogen fuel. The nanocomposite material could also potentially be useful in devices that convert carbon dioxide into hydrocarbon fuels such as methane.

These materials can be manipulated in such a way that when sunlight strikes them the free electrons generated can easily move from one energy level to another—or jump across the different materials—and be efficiently converted to electricity.

Nanotech Research Related to Solar Cells

In 2012, MIT researchers developed a solar cell using graphene coated with ZnO nanowires, a method that is believed to enable production of low cost, flexible solar cells with reasonable efficiency. Researchers are also very close to making solar cells using single molecule thick graphene sheets, which could generate about 1000 times more power than conventional solar cells.

In 2013, Michigan Technological University researchers developed a honeycomb like 3D graphene structure that has graphene sheets held by lithium carbonate. This nanostructure was able to achieve 7.8% conversion of light to electricity.

More recently in 2018, Niels Bohr Institute researchers found that sunlight can be concentrated in nanowires, thanks to a resonance effect. This can be used to produce more efficient solar cells by harvesting more sunlight and converting it to electricity. Also, researchers at Los Alamos National Lab made a solar cell using a copper indium selenide sulfide quantum dots, which are both low cost and nontoxic, unlike lead or cadmium quantum dots.

References and Further Reading

  • New nanostructured thin film shows promise for efficient solar energy conversion - Nanotech Now
  • Nanotechnology to make inexpensive solar cells more efficient - Foresight
  • Nanotechnology in Solar Cells - Understanding Nano

Acknowledgment

Sources of funding for this research included the U.S. Department of Energy, the National Science Foundation of China, and the University of California Institute for Mexico and the United States (UC-MEXUS).

Research collaborators included Abraham Wolcott, Li-ping Xu and Shaowei Chen at UCSC; Zhenhai Wen and Jinghong Li at Tsinghua University in Beijing, China; and Elder De La Rosa of the Centro de Investigaciones en Optica, A.C., in Leon, Guanajuato, Mexico.

Source: UC Santa Cruz
Last Update 10th January 2008

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