The cell phones in our pockets and hundreds of other devices rely on semiconductors embedded in electronic circuits. Silicon is a common semiconductor material that is also used in photovoltaic (PV) solar panels that convert the sun’s energy into useful electricity.
One of Nikolai Kouklin’s research goals is to find viable alternatives to silicon for solar cells and other nanotechnology applications. These alternative materials may be less efficient individually, but have an improved cost-to-efficiency ratio.
Kouklin, professor, electrical engineering, whose experimental work has been mainly funded by the National Science Foundation, is especially excited about so-called gapless Dirac semimetals. An example of these is cadmium arsenide, a recently re-discovered bulk material with properties similar to graphene.
“Graphene, which consists of a single layer of carbon atoms, can be now synthesized cost-effectively, but the high variability of its properties makes its commercial adaptation difficult,” Kouklin says. “My lab has recently developed a fast and low-temperature fabrication process for electronic-grade cadmium arsenide bulk crystals. That makes cadmium arsenide a very promising next-generation material with potential for application beyond electronics.”
Backing up that claim, Kouklin has shown that the room-temperature ZT value for cadmium arsenide, which describes its thermal-to-electrical power converting ability, exceeds that of commercial thermoelectric materials by a factor greater than three.
Kouklin also uses carbon nanotubes to build a new class of junctionless photothermovoltaic (PTV) cells. When light excites the familiar PV cell, it generates a voltage difference and thus electrical current. But when photons excite a PTV cell, the temperature on the light-absorbing side increases significantly. The temperature difference between the cell’s cold and hot sides induces the voltage difference, a phenomenon known as the Seebeck effect. As carbon nanotubes can be metallic, in principle, almost all sun wavelengths can be harvested, whereas only roughly half of solar radiation can be tapped by Si-PV cells.
With Konstantin Sobolev, professor, civil & environmental engineering, Kouklin has explored yet another type of solar energy harvesting in a pioneering proof-of-concept study
of concrete-embedded dye-sensitized solar cells (DSCCs). Originally invented in Switzerland, they are made by attaching organic dye to titanium dioxide nanoparticles embedded into the surface of carbon nanotube-modified concrete.
“Having concrete structures, such as buildings and roads, generate on-site electricity would be of great interest in urban settings,” Kouklin says. “But in order to advance beyond proof-of-concept, we still need to improve the efficiency of this new type of DSCC to make them commercially attractive.”
Beyond solar cells, Kouklin also develops advanced self-powered nano-photodetectors for infrared light—the invisible wavelength that we feel as heat—for applications that range from military surveillance to deep tissue medical imaging and the fingerprinting of biological molecules.