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"This structure is something known as a perovskite crystal"
A New Solar Material Shows Its Potential
A new material described in Nature adds to the momentum suggesting a new path to high-efficiency, inexpensive solar cells.
By Kevin Bullis on November 10, 2013
...A new solar cell material has properties that might lead to solar cells more than twice as efficient as the best on the market today. An article this week in the journal Nature describes the materials—a modified form of a class of compounds called perovskites, which have a particular crystalline structure.
The researchers haven’t yet demonstrated a high efficiency solar cell with the material. But their work adds to a growing body of evidence suggesting perovskite materials could change the face of solar power. Researchers are making new perovskites using combinations of elements and molecules not seen in nature; many researchers see the materials as the next great hope for making solar power cheap enough to compete with fossil fuels.
Perovskite-based solar cells have been improving at a remarkable pace. It took a decade or more for the major solar cell materials used today—silicon and cadmium telluride—to reach efficiency levels that have been demonstrated with perovskites in just four years. The rapid success of the material has impressed even veteran solar researchers who have learned to be cautious about new materials after seeing many promising ones come to nothing (see “A Material that Could Make Solar Power ‘Dirt Cheap’”).
The perovskite material described in Nature has properties that could lead to solar cells that can convert over half of the energy in sunlight directly into electricity, says Andrew Rappe, co-director of Pennergy, a center for energy innovation at the University of Pennsylvania, and one of the new report’s authors. That’s more than twice as efficient as conventional solar cells. Such high efficiency would cut in half the number of solar cells needed to produce a given amount of power. Besides reducing the cost of solar panels, this would greatly reduce installation costs, which now account for most of the cost of a new solar system.
Unlike conventional solar cell materials, the new material doesn’t require an electric field to produce an electrical current...
A new material described in Nature adds to the momentum suggesting a new path to high-efficiency, inexpensive solar cells.
By Kevin Bullis on November 10, 2013
...A new solar cell material has properties that might lead to solar cells more than twice as efficient as the best on the market today. An article this week in the journal Nature describes the materials—a modified form of a class of compounds called perovskites, which have a particular crystalline structure.
The researchers haven’t yet demonstrated a high efficiency solar cell with the material. But their work adds to a growing body of evidence suggesting perovskite materials could change the face of solar power. Researchers are making new perovskites using combinations of elements and molecules not seen in nature; many researchers see the materials as the next great hope for making solar power cheap enough to compete with fossil fuels.
Perovskite-based solar cells have been improving at a remarkable pace. It took a decade or more for the major solar cell materials used today—silicon and cadmium telluride—to reach efficiency levels that have been demonstrated with perovskites in just four years. The rapid success of the material has impressed even veteran solar researchers who have learned to be cautious about new materials after seeing many promising ones come to nothing (see “A Material that Could Make Solar Power ‘Dirt Cheap’”).
The perovskite material described in Nature has properties that could lead to solar cells that can convert over half of the energy in sunlight directly into electricity, says Andrew Rappe, co-director of Pennergy, a center for energy innovation at the University of Pennsylvania, and one of the new report’s authors. That’s more than twice as efficient as conventional solar cells. Such high efficiency would cut in half the number of solar cells needed to produce a given amount of power. Besides reducing the cost of solar panels, this would greatly reduce installation costs, which now account for most of the cost of a new solar system.
Unlike conventional solar cell materials, the new material doesn’t require an electric field to produce an electrical current...
http://www.technologyreview.com/news/521491/a-new-solar-material-shows-its-potential/
This next piece is based on the same Nature article, but it spends some effort to explain the nature of the two relevant "paradigms". The thread title if a line from below.
New paradigm for solar cell construction demonstrated
(Phys.org)...
...Existing solar cells all work in the same fundamental way: they absorb light, which excites electrons and causes them to flow in a certain direction. This flow of electrons is electric current. But to establish a consistent direction of their movement, or polarity, solar cells need to be made of two materials. Once an excited electron crosses over the interface from the material that absorbs the light to the material that will conduct the current, it can't cross back, giving it a direction.
"There's a small category of materials, however, that when you shine light on them, the electron takes off in one particular direction without having to cross from one material to another," Rappe said. "We call this the 'bulk' photovoltaic effect, rather than the 'interface' effect that happens in existing solar cells. This phenomenon has been known since the 1970s, but we don't make solar cells this way because they have only been demonstrated with ultraviolet light, and most of the energy from the sun is in the visible and infrared spectrum."
<snip>
Starting more than five years ago, the team began theoretical work, plotting the properties of hypothetical new compounds that would have a mix of these traits. Each compound began with a "parent" material that would impart the final material with the polar aspect of the bulk photovoltaic effect. To the parent, a material that would lower the compound's bandgap would be added in different percentages. These two materials would be ground into fine powders, mixed together and then heated in an oven until they reacted together. The resulting crystal would ideally have the structure of the parent but with elements from the second material in key locations, enabling it to absorb visible light.
"The design challenge," Davies said, "was to identify materials that could retain their polar properties while simultaneously absorbing visible light. The theoretical calculations pointed to new families of materials where this often mutually exclusive combination of properties could in fact be stabilized."
<snip>
(Phys.org)...
...Existing solar cells all work in the same fundamental way: they absorb light, which excites electrons and causes them to flow in a certain direction. This flow of electrons is electric current. But to establish a consistent direction of their movement, or polarity, solar cells need to be made of two materials. Once an excited electron crosses over the interface from the material that absorbs the light to the material that will conduct the current, it can't cross back, giving it a direction.
"There's a small category of materials, however, that when you shine light on them, the electron takes off in one particular direction without having to cross from one material to another," Rappe said. "We call this the 'bulk' photovoltaic effect, rather than the 'interface' effect that happens in existing solar cells. This phenomenon has been known since the 1970s, but we don't make solar cells this way because they have only been demonstrated with ultraviolet light, and most of the energy from the sun is in the visible and infrared spectrum."
<snip>
Starting more than five years ago, the team began theoretical work, plotting the properties of hypothetical new compounds that would have a mix of these traits. Each compound began with a "parent" material that would impart the final material with the polar aspect of the bulk photovoltaic effect. To the parent, a material that would lower the compound's bandgap would be added in different percentages. These two materials would be ground into fine powders, mixed together and then heated in an oven until they reacted together. The resulting crystal would ideally have the structure of the parent but with elements from the second material in key locations, enabling it to absorb visible light.
"The design challenge," Davies said, "was to identify materials that could retain their polar properties while simultaneously absorbing visible light. The theoretical calculations pointed to new families of materials where this often mutually exclusive combination of properties could in fact be stabilized."
<snip>
Read more at: http://phys.org/news/2013-11-paradigm-solar-cell.html#jCp
