Nano-crystals stake claim in solar panel research

Cheap and easy to make

Researchers in the US have developed ultra-thin solar cells made entirely of inorganic nano-crystals. The team says it is the first time something like this has been accomplished, and hints that it is the first step towards cheap and efficient solar paneling.

The new material can't yet convert sunlight into electricity as efficiently as traditional silicon solar cells, but it is an easy match for the organic alternative. In addition, their efficiency seems to improve over time, the Berkeley Lab researchers say, rather than degrading, as with plastic photo-cells.

The nano-crystals are also as cheap and easy to make as plastic solar cells but have the added advantage of being stable in air, the researchers say.

Writing in the journal Science, the team describes the fabrication technique they developed.

They separately synthesized rod-shaped nanometre scale crystal of two semi-conductors: cadmium selenide and cadmium telluride. The crystals were then dissolved in solution and spin-cast on to a conductive glass substrate.

This process produces films that are around a thousand times thinner than a human hair capable of converting sunlight to electricity with around a three per cent efficiency rate. Silicon photovolatics, by contrast, have an efficiency of between eight and 13 per cent, depending on the design.

"We obviously still have a long way to go in terms of energy conversion efficiency," said Ilan Gur, co-author on the paper. "But our dual nano-crystal solar cells are ultra-thin and solution-processed, which means they retain the cost-reduction potential that has made organic cells so attractive vis-a-vis their conventional semiconductor counterparts."

Paul Alivisatos, Chancellor's Professor of Chemistry and Materials Science at UC Berkeley notes: "A solar cell that relies exclusively on colloidal nano-crystals has been anticipated theoretically in recent years. We've now demonstrated such a device and have presented a mechanism for its operation." ®

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