The solar cell created is actually a hybrid, comprised of tiny nanorods dispersed in an organic polymer or plastic. A layer only 200 nanometers thick is sandwiched between electrodes and can produce at present about .7 volts. The electrode layers and nanorods /polymer layers could be applied in separate coats, making production fairly easy. And unlike today’s semiconductor-based photovoltaic devices, plastic solar cells can be manufactured in solution in a beaker without the need for clean rooms or vacuum chambers.
The technology takes advantage of recent advances in nanotechnology specifically the production of nanocrystals and nanorods. These are chemically pure clusters of 100 to 100000 atoms with dimensions of the order of a nanometer, or a billionth of a meter. Because of their small size, they exhibit unusual and interesting properties governed by quantum mechanics, such as the absorption of different colors of light depending upon their size. Nanorods were made of a reliable size out of cadmium selenide, a semi conducting material.
Nanorods are manufactured in a beaker containing cadmium selenide, aiming for rods of diameter-7 nanometers to absorb as much sunlight as possible. The length of the nanorods may be approximately 60nanometers.Then the nanorods are mixed with a plastic semiconductor called p3ht-poly-(3-hexylthiophene) a transparent electrode is coated with the mixture.
The thickness, 200 nanometers-a thousandth the thickness of a human hair-is a factor of 10 less than the micron-thickness of semiconductor solar cells. An aluminium coating acting as the back electrode completed the device. The nanorods act like wires. When they absorb light of a specific wavelength, they generate an electron plus an electron hole-a vacancy in the crystal that moves around just like an electron. The electron travels the length of the rod until it is collected by aluminium electrode. The hole is transferred to the plastic, which is known as a hole-carrier, and conveyed to the electrode, creating a current.
Some of the obvious improvements include better light collection and concentration, which already are employed in commercial solar cells. Significant improvements can be made in the plastic, nanorods mix, too, ideally packing the nanorods closer together, perpendicular to the electrodes, using minimal polymer, or even none-the nanorods would transfer their electrons more directly to the electrode. In their first-generation solar cells, the nanorods are jumbled up in the polymer, leading to losses of current via electron-hole recombination and thus lower efficiency.
They also hope to tune the nanorods to absorb different colors to span the spectrum of sunlight. An eventual solar cell has three layers each made of nanorods that absorb at different wavelength.
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