Sol Voltaics and a group of scientists from Lund University believe that semiconductor nanowires are the way forward for a world with better solar cells. With their patented Aerotaxy process, they aim to manufacture low-cost gallium arsenide solar cells.
But first, what are solar cells and how do they work? Solar cells essentially harvest energy from the Sun or other light sources and turn it into electrical energy. In simple terms, light hits the solar cell and knocks electrons out which can then flow as a current. The effect of knocking electrons out of a substance with light is known as the photoelectric effect and was the reason why Einstein thought that light could be described as quanta (discrete packets) of energy. This was described in his 1905 paper which won him a Nobel Prize in Physics in 1921.
Solar cells are semiconductors which exhibit the photoelectric effect when light is incident on them. A semiconductor is a material that has a conductivity in the middle of an insulator and conductor. You can think of semiconductors as diodes, they only allow current to flow in one direction. They have a p-n junction which consists of a p-type material and an n-type material. N-type materials are electron rich and p-type materials are electron deficit. When these materials are put in contact, the region between them is known as the p-n junction and no current flows across this junction. This region is normally known as the depletion region and is neutral overall. Since, current cannot flow over this region, the electrons can only move via an external path, much like a diode.
Instead of using a planar material, like in most semiconductors, the team of scientists have found that using a periodic nanowire array produces the same amount of current but with significantly less material. They produced gallium arsenide nanowires using their Aerotaxy system which will be able to offer a module efficiency of larger than 27% which is a 50% improvement than current solar panels .
The system involves using an aerosol generator to produce catalytic seed particles where growth reactor is added to promote growth of nanowires. Extremely high growth rates are achieved without the need for a substrate. The team were the first to prove that p-n junctions with excellent diode characteristics could be created in this way. This technique is appealing since it is low-cost and can be used to mass-produce solar cells. Their work was published in the latest issue of Nano Letters. Nanowires are perfect for solar cells as they guide the light onto the solar cells without the need for optical or mechanical aid.
Industrial-scale production of nanowire-based solar cells could be the way forward for solar cell technology. So watch this space for new nanowire-based solar cells.
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