New method lights a path for solar cells
1
New method lights a path for solar cells Using a technique in which chemical ingredients assemble themselves, a re- search team has developed a potentially inexpensive way of making solar cells. So far, high cost has hampered the largescale use of solar energy systems. Solar cells, also known as photovoltaic cells, transform photons into electric cur- rent without producing pollution. Com- mercially available solar cells already con- vert sunlight efficientlyenough for certain applications, such as satellites, notes J. Devin MacKenzie of the University of Cambridge in England. The widespread use of solar power has been elusive because it can be difficult and costly to manufacture the commercial photovoltaic cells, which are made of inor- ganic crystals such as silicon, MacKenzie says. Some researchers have tried to circum- vent this problem by creating photovolta- ic cells from organic components that they can process as easily as plastics. Some of these cells remain in various stages of development,but none are close to becoming commerciallysuccessful. In the Aug. 10 SCIENCE, MacKenzie and his colleagues report a development that they say could develop into a particularly simple way of making organic solar cells. Their new cell-which they claim is nearly as efficient as the best organic solar cells already made-contains a liquid crystal called peri-hexabenzocoronene and an organic dye called perylene. When poured onto a flat surface, the ingredients arrange themselves into a two-layered film with an internal structure that promotes electron flow. This simple self-assembly offers a PO- tential new route toward low-cost, mass production of organic solar cells, com- ments Jenny Nelson of Imperial College in London. Other organic solar cells current- ly operate a bit more efficiently, she says, but “potentially, [the new technique] could lead to better performance.” “This is a beautiful example of combin- ing molecular engineering with nanoscale self-assembly,” adds Alan J. Heeger of the University of California, Santa Barbara and a recent Nobel laureate for his work on conductive polymers (SN 10/14/00, p. 247). “They have made an important step forward toward the goal of low-cost, high- efficiency, organic photovoltaic cells.” In general, organic cells offer certain benefits over inorganic ones, Nelson says. For example, organic cells might be made in different colors and be flexible enough to use on window blinds, walls, and other materials in buildings. This provides de- sign options that could lower the cost of Fighter-pilot dogfights no longer blaze across the night skies of Europe, but other fliers may still duel to the death up there. Researchers in Spain propose that bats hunt down migrating birds in midair. The biggest bat in Europe, the greater noctule, or Nyctalus lasiopterus, eats many birds during the spring and fall mi- grations, says Javier Juste of Doiiana Bi- ological Station in Seville. He and his col- leagues reached that conclusion after analyzing 14,000 bat droppings during the course of a year. “It’s the only bat known to get the profit of migrating birds,” Juste says. Birds by the millions stream over Eu- rope between winter havens in Africa and northerly breeding grounds. For a predator, the mass of birds is “a big, big chocolate bar coming by,”Juste says. Most of the world’s bats dine on in- sects or fruit. Yet a handful can take on bigger and livelier prey, swooping down to pluck fish out of the water, silence a frog in midcroak, or grab a lizard off a wall. Around a dozen bat species, most- ly in the tropics, snatch roosting birds from their perches, says Juste. He suspects that the greater noctule doesn’t wait for its meal to come home to roost. Several lines of evidence sug- Bat bites bird .. in migration attacks gest that this bat attacks birds on the wing, say Juste, his Doiiana colleague Carlos Ib&iez, and their coauthors in the Aug. 14 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. Three noctule populations take ad- vantage of birds’ seasonal migrations, the researchers report. As many as 45 percent of the analyzed droppings car- ried feathers during the March-to-May and August-teNovember runs. On two occasions, researchers found bats with, or near, identifiable bits from a Euro- pean robin or a warbler. In June and Ju- ly, the bats went back to eating insects, and barely 1 percent of bat droppings had feathers. Several traits suggest that the greater noctule specializes in long-range hunt- ing, the researchers find. The bat spreads long, relatively narrow wings built more for speed than for close- range maneuverability in forests. Also, the echolocation calls that the team recorded are typical of those used by open-air species. Though low for a bat, the calls are still too high in pitch for birds to hear, Juste adds. As he pictures it, the bats “take ad- vantage of millions of birds flying at night, tired, blind, probably flying me- chanically,trying to get to Africa.” 86 SCIENCE NEWS, VOL. 160 I - I A new organic film for making solar cells. Atomic-forcemicroscopy shows it at two magnifications. using the cells. High hurdles remain, however. For one, the efficiency of organic solar cells doesn’t approach that of the harder-to-make inor- ganic ones. The best organic cells convert a little more than 2 percent of sunlight into electric current, while commercial inor- ganic cells reach efficiencies of 20 percent, Nelson says. It remains to be seen whether the new technique, others in development, or a completely unforeseen one will eventually win out, says Nelson. -.I Gorman Juste speculates that a bat swoops onto an unsuspecting bird and must dis- able it before plummeting to the ground. “The bat has very strong neck muscles and formidable teeth,” he says, so he suspects that a few bites do the job. The bats may even eat the birds in midair, according to Juste. The team found no heaps of bird leftovers under the bats’ roosts. After considering how bats eat large, airborne beetles, Juste suspects that the greater noctules strip off a bird’s wings. “They take a couple of big bites of the breast and then throw the bird away,” he suggests. Bat researcher Richard Lava1 in Mon- teverde, Costa Rica, calls the suggestion of airborne hunts “fascinating.”The pa- per presents “amazing data,” though the question of how the bat catches the bird remains open, he says. Kent Rylander of Texas Tech Universi- ty in Lubbock adds, “I’m a little sur- prised that the scientific community has been so long in discovering this obvious niche for nocturnal bats.” He calls the team’s arguments “convincing.” Juste recognizes the difficulties of making the case by indirect evidence. For skeptical researchers, he says, “we have plenty of bat droppings, and they are more than welcome to look at them.” 4. Milius AUGUST 11 2001
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Transcript of New method lights a path for solar cells
New method lights a path for solar cells Using a technique in which chemical
ingredients assemble themselves, a re- search team has developed a potentially inexpensive way of making solar cells. So far, high cost has hampered the largescale use of solar energy systems.
Solar cells, also known as photovoltaic cells, transform photons into electric cur- rent without producing pollution. Com- mercially available solar cells already con- vert sunlight efficiently enough for certain applications, such as satellites, notes J. Devin MacKenzie of the University of Cambridge in England.
The widespread use of solar power has been elusive because it can be difficult and costly to manufacture the commercial photovoltaic cells, which are made of inor- ganic crystals such as silicon, MacKenzie says.
Some researchers have tried to circum- vent this problem by creating photovolta- ic cells from organic components that they can process as easily as plastics. Some of these cells remain in various stages of development, but none are close to becoming commercially successful.
In the Aug. 10 SCIENCE, MacKenzie and his colleagues report a development that they say could develop into a particularly simple way of making organic solar cells. Their new cell-which they claim is nearly
as efficient as the best organic solar cells already made-contains a liquid crystal called peri-hexabenzocoronene and an organic dye called perylene. When poured onto a flat surface, the ingredients arrange themselves into a two-layered film with an internal structure that promotes electron flow.
This simple self-assembly offers a PO- tential new route toward low-cost, mass production of organic solar cells, com- ments Jenny Nelson of Imperial College in London. Other organic solar cells current- ly operate a bit more efficiently, she says, but “potentially, [the new technique] could lead to better performance.”
“This is a beautiful example of combin- ing molecular engineering with nanoscale self-assembly,” adds Alan J. Heeger of the University of California, Santa Barbara and a recent Nobel laureate for his work on conductive polymers (SN 10/14/00, p. 247). “They have made an important step forward toward the goal of low-cost, high- efficiency, organic photovoltaic cells.”
In general, organic cells offer certain benefits over inorganic ones, Nelson says. For example, organic cells might be made in different colors and be flexible enough to use on window blinds, walls, and other materials in buildings. This provides de- sign options that could lower the cost of
Fighter-pilot dogfights no longer blaze across the night skies of Europe, but other fliers may still duel to the death up there. Researchers in Spain propose that bats hunt down migrating birds in midair.
The biggest bat in Europe, the greater noctule, or Nyctalus lasiopterus, eats many birds during the spring and fall mi- grations, says Javier Juste of Doiiana Bi- ological Station in Seville. He and his col- leagues reached that conclusion after analyzing 14,000 bat droppings during the course of a year.
“It’s the only bat known to get the profit of migrating birds,” Juste says. Birds by the millions stream over Eu- rope between winter havens in Africa and northerly breeding grounds. For a predator, the mass of birds is “a big, big chocolate bar coming by,” Juste says.
Most of the world’s bats dine on in- sects or fruit. Yet a handful can take on bigger and livelier prey, swooping down to pluck fish out of the water, silence a frog in midcroak, or grab a lizard off a wall. Around a dozen bat species, most- ly in the tropics, snatch roosting birds from their perches, says Juste.
He suspects that the greater noctule doesn’t wait for its meal to come home to roost. Several lines of evidence sug-
Bat bites bird . . in migration attacks gest that this bat attacks birds on the wing, say Juste, his Doiiana colleague Carlos Ib&iez, and their coauthors in the Aug. 14 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES.
Three noctule populations take ad- vantage of birds’ seasonal migrations, the researchers report. As many as 45 percent of the analyzed droppings car- ried feathers during the March-to-May and August-teNovember runs. On two occasions, researchers found bats with, or near, identifiable bits from a Euro- pean robin or a warbler. In June and Ju- ly, the bats went back to eating insects, and barely 1 percent of bat droppings had feathers.
Several traits suggest that the greater noctule specializes in long-range hunt- ing, the researchers find. The bat spreads long, relatively narrow wings built more for speed than for close- range maneuverability in forests. Also, the echolocation calls that the team recorded are typical of those used by open-air species.
Though low for a bat, the calls are still too high in pitch for birds to hear, Juste adds. As he pictures it, the bats “take ad- vantage of millions of birds flying at night, tired, blind, probably flying me- chanically, trying to get to Africa.”
86 SCIENCE NEWS, VOL. 160
I- I A new organic film for making solar cells. Atomic-force microscopy shows it at two magnifications.
using the cells. High hurdles remain, however. For one,
the efficiency of organic solar cells doesn’t approach that of the harder-to-make inor- ganic ones. The best organic cells convert a little more than 2 percent of sunlight into electric current, while commercial inor- ganic cells reach efficiencies of 20 percent, Nelson says.
It remains to be seen whether the new technique, others in development, or a completely unforeseen one will eventually win out, says Nelson. -.I Gorman
Juste speculates that a bat swoops onto an unsuspecting bird and must dis- able it before plummeting to the ground. “The bat has very strong neck muscles and formidable teeth,” he says, so he suspects that a few bites do the job.
The bats may even eat the birds in midair, according to Juste. The team found no heaps of bird leftovers under the bats’ roosts.
After considering how bats eat large, airborne beetles, Juste suspects that the greater noctules strip off a bird’s wings. “They take a couple of big bites of the breast and then throw the bird away,” he suggests.
Bat researcher Richard Lava1 in Mon- teverde, Costa Rica, calls the suggestion of airborne hunts “fascinating.” The pa- per presents “amazing data,” though the question of how the bat catches the bird remains open, he says.
Kent Rylander of Texas Tech Universi- ty in Lubbock adds, “I’m a little sur- prised that the scientific community has been so long in discovering this obvious niche for nocturnal bats.” He calls the team’s arguments “convincing.”
Juste recognizes the difficulties of making the case by indirect evidence. For skeptical researchers, he says, “we have plenty of bat droppings, and they are more than welcome to look at them.”
4. Milius
AUGUST 11 2001
