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Usable Quantum Dot Solar Cells Finally Produced at NREL

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A new type of solar cell developed by a team of researchers from the National Renewable Energy Laboratory in Golden, Colorado, is able to harvest the energy that photovoltaic cells usually lose as heat. Although the efficiency is for now only 5 percent, the process could be improved in the future.

The researchers led by Arthur Nozik has created the first “MEG” (Multiple Exciton Generation) solar cell after learning from other scientists’ successes and failures. Until now, this type of cell existed only on paper and in partially complete projects, and made use of nanometer-sized particles called “quantum dots.”

The interesting fact about quantum dots is that, when hit by light, they can displace a number of electrons greater than the number of photons that hit them, thus making the photon-electron conversion more efficient.

Quantum dots can make use of the higher-frequency and higher-energy parts of the light spectrum, such as violets and ultraviolets. Because they carry too much power for a normal solar cell to convert efficiently, they usually just dissipate as heat. The heat usually gets discarded or converted to electricity through classic methods, such as steam turbines or newer thermoelectric materials, but the equipment used to do that tends to be expensive and bulky.

Nozik’s team treated the quantum dots with two colorless liquids: hydrazine and 1,2-ethanedithiol, which made electrical charges move more freely, resulting in a 5 percent conversion efficiency.

Today’s silicon solar cells, however, feature 20+ percent efficiency, but the quantum dots approach will get better when the researchers will find ways to make the dots more sensitive to light.

Ultimately, quantum dot solar cells will probably become, in a few years from now, what dye-sensitized cells have become since the beginning of the 90s, when they had been invented, and the solar technology will hit new territories and new boundaries that nobody thought existed before.

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