Solar cells convert light into electricity. While the sun is one source of light, the burning of natural resources like oil and natural gas can also be harnessed.
However, solar cells do not convert all light to power equally, which has inspired a joint industry-academia effort to develop a potentially game-changing solution.
“Current solar cells are not good at converting visible light to electrical power. The best efficiency is only around 20%,” explains Kyoto University’s Takashi Asano, who uses optical technologies to improve energy production.
Higher temperatures emit light at shorter wavelengths, which is why the flame of a gas burner will shift from red to blue as the heat increases. The higher heat offers more energy, making short wavelengths an important target in the design of solar cells.
“The problem,” continues Asano, “is that heat dissipates light of all wavelengths, but a solar cell will only work in a narrow range.
“To solve this, we built a new nano-sized semiconductor that narrows the wavelength bandwidth to concentrate the energy.”
Previously, Asano and colleagues of the Susumu Noda lab had taken a different approach. “Our first device worked at high wavelengths, but to narrow output for visible light required a new strategy, which is why we shifted to intrinsic silicon in this current collaboration with Osaka Gas,” says Asano.
To emit visible wavelengths, a temperature of 1000?C was needed, but conveniently silicon has a melting temperature of over 1400?C. The scientists etched silicon plates to have a large number of identical and equidistantly-spaced rods, the height, radii, and spacing of which was optimized for the target bandwidth.
According to Asano, “the cylinders determined the emissivity,” describing the wavelengths emitted by the heated device.
Using this material, the team has shown in Science Advances that their nanoscale semiconductor raises the energy conversion rate of solar cells to at least 40%.
“Our technology has two important benefits,” adds lab head Noda. “First is energy efficiency: we can convert heat into electricity much more efficiently than before. Secondly is design. We can now create much smaller and more robust transducers, which will be beneficial in a wide range of applications.”
Learn more: A big nano boost for solar cells
An international research team is developing nanotechnology-based applications of hexanal, a natural plant extract that extends the storage life of harvested fruit.
Bananas, mangoes and papayas: these tender tropical fruits are in high demand in export markets and an important livelihood source for producers. But freshness is key because these fruits spoil quickly and damage easily. The challenge is especially daunting where refrigeration is lacking. Estimates suggest that up to 40% of produce in tropical countries is lost in post-harvest handling.
Breakthrough research by Canadian, Indian, and Sri Lankan partners points to a promising innovation: nanotech applications of a natural plant extract called hexanal can be used to delay fruit ripening. Hexanal inhibits a plant enzyme that is responsible for breaking cell membranes during a fruit’s ripening process.
In initial research in India and Sri Lanka, scientists used a hexanal-impregnated formula to test the product on mangoes. Spraying orchards with a low concentration of the compound slowed fruit ripening by three weeks. The team is also developing “smart packaging” systems, made from materials such as banana fibre, that slowly release hexanal to extend storage life after fruit is harvested.
These applications can boost farmers’ incomes. “Let’s say a mango farmer sprays half or one third of the orchard with the formulation,” explains Jay Subramanian, a professor at Canada’s University of Guelph. “He gets that same mango production but spread out over a three- to four-week window instead of just one week, which causes a major rush and a glut in the market, leading to low prices.”
In field trials, farmers were able to earn up to 15% more for their crop. Once harvested, the sprayed mangoes remained fresh for up to 26 days in cold storage and 17 days at room temperature.