Researchers at Rice University in Texas developed a nano-antenna that, when attached to silicon used for solar cells, enables the semiconductor material to detect infrared light. One-third of solar energy that comes to the Earth is infrared, but majority of solar panels cannot use that wavelength. The researchers thus tried to combine the metallic nanoscale antenna optics with semiconductor electronics to allow for the detection of the infrared wavelength.
“There’s no practical way to directly detect infrared light with silicon, but we’ve shown that it is possible if you marry the semiconductor to a nano-antenna,” said the lead researcher Naomi Halas.
“We expect this technique will be used in new scientific instruments for infrared light detection and for higher-efficiency solar cells,” she added.
Semiconductors, like silicon, have a band gap that can only detect certain frequencies of light. These frequencies do not include infrared.
The new metal nano-antenna’s structure is a highly compact, wavelength-resonant and polarization-specific light detector. These features enable it to extend its response to energies below the semiconductor band edge, thereby enabling it to detect infrared.
Generating current
To generate an electrical current from infrared, the research team used the hot electrons that resulted from decaying plasmons, waves of energy created when infrared light hit the antenna.
Where the metallic nano-antenna and the semiconductor material join, a barrier known as the “Schottky barrier” is created.
The researchers showed that the infrared light striking the antenna would result in a hot electron that can jump this barrier and create an electric current.
“The nano-antenna-diodes we created to detect plasmon-generated hot electrons are already pretty good at harvesting infrared light and turning it directly into electricity,” said Mark Knight, lead author on the paper.
“We are eager to see whether this expansion of light-harvesting to infrared frequencies will directly result in higher-efficiency solar cells,” Mr. Knight noted.
Infrared wavelength for solar cells has been studied by different institutions to develop solar panel light conversion efficiency.
Xiamen University in China and the University of North Carolina had developed a device to absorb infrared light. They used a nanowire made from zinc selenide to form a material structure known as a type-II heterojunction. When used in an array, the design can absorb light from the visible and near-infrared wavelengths.
Meanwhile, the Massachusetts Institute of Technology was able to develop a transparent photovoltaic solar cell that can only harvest infrared light for energy. Their transparent PV solar cell currently has an efficiency of 1.7 percent which they expect to reach 12 percent with further development.
