A research team from Tel Aviv University is working on a solar panel composed of nano-antennas instead of semiconductors. By adapting classic metallic antennas to absorb light waves at optical frequencies, a much higher conversion rate from light into useable energy can be achieved.
Such efficiency, combined with a lower material cost, would mean a cost-effective way to harvest and utilize the energy. The team consists of professors Koby Scheuer, Yael Hanin, and Amir Boag of the university's Department of Physical Electronics.
Both radio and optical waves are electromagnetic energy, Scheuer explains. When these waves are harvested, electrons are generated that can be converted into electric current. Traditionally, detectors based on semiconducting materials like silicon are used to interface with light, while radio waves are captured by antenna.
For optimal absorption, the antenna dimensions must correspond to the light's very short wavelength. To test the efficacy of their antennas, Scheuer and his team measured their ability to absorb and remit energy. "In order to function, an antenna must form a circuit, receiving and transmitting," says Scheuer, who points to the example of a cell phone, whose small, hidden antenna both receives and transmits radio waves in order to complete a call or send a message.
By illuminating the antennas, the researchers were able to measure the antennas' ability to re-emit radiation efficiently, and determine how much power is lost in the circuit. Initial tests indicate that 95 percent of the wattage going into the antenna comes out, meaning that only five percent is wasted.
According to Scheuer, these antennas also have greater potential for solar energy because they can collect wavelengths across a much broader spectrum of light. The solar spectrum has UV or infrared rays ranging from ten microns to less than two hundred nanometers. No semiconductor can handle this broad a spectrum, and they absorb only a fraction of the available energy. A group of antennas, however, can be manufactured in different lengths with the same materials and process, exploiting the entire available spectrum of light.
When finished, the team's new solar panels will be large sheets of plastic which, with the use of a nano-imprinting lithography machine, will be imprinted with varying lengths and shapes of metallic antennas.