Atomically Thin, Flexible, And Transparent Solar Panels May Soon Cover Building Facades
The quest to discover thinner, lighter materials for scientific projects never ends. Just as the miracle material graphene was touted as the thinnest material to have special electronic properties, scientists have discovered another material as thin as graphene with even better photovoltaic properties, which can convert solar light into a direct current. Created by scientists from the Vienna University of Technology, the new material, tungsten diselenide, can be arranged in single or multiple atomic layers to create extremely thin, flexible solar cells, and mounted onto building facades.
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Isolating single-atom-thick graphene crystals from graphite was groundbreaking at the time, and it earned its creators a Nobel Prize in physics in 2010. Since then, the two dimensional allotrope of carbon has been used widely in electronics, water purifiers, semiconductors, electrodes, and solar cells, to name a few. Its potential uses in myriad applications have been recognized by innovators around the world, and in 2013 the EU approved a funding of one billion euros for grapheme-based research. Its ability to endure extreme mechanical strain makes it an ideal candidate for use in optoelectronic and nanoelectronic applications. Graphene, as a light sensor, can efficiently convert optical signals into electric pulses on short timescales.
But graphene has one shortcoming that prevents it from being ideal for use in solar cells.
"The electronic states in graphene are not very practical for creating photovoltaics," said
Professor Thomas Mueller, of the Photonics Institute at Vienna University, in a statement. Given this limitation, Mueller and his team were looking for an ultrathin material with photovoltaic properties. They zeroed in on tungsten diselenide, a compound consisting of one layer of tungsten atoms arranged in a hexagonal pattern, interconnected with multiple selenium atoms above and below it. It has excellent photovoltaic properties and can convert absorbed light into electric power.
As an extremely thin layer, tungsten diselenide absorbs only five percent of total light - the remaining 95 percent just passes through it. One-tenth of the absorbed light is converted into electrical power, giving it high internal efficiency. If several layers of the ultrathin material are stacked on top of each other, their rate of absorbing light would be higher, although the researchers say that the material's transparency could be useful. "We are envisioning solar cell layers on glass facades, which let part of the light into the building while at the same time creating electricity," Mueller said in the release.
Conventional solar cells made of silicon are bulky and inflexible. When they're made with organic material like conjugated polymers, they have a short shelf life. So the ultrathin tungsten diselenide offers an excellent replacement for the semiconductors used today. "A big advantage of two-dimensional structures of single atomic layers is their crystallinity. Crystal structures lend stability," Mueller said. Tungsten diselenide is fast becoming a go-to material choice for scientific applications, just like graphene did before it.
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