Inexpensive, Highly Efficient and Flexible Solar Cells Developed at Caltech

A team of scientists at the California Institute of technology (Caltech) have just published their research on solar cells that will be thinner, lighter, more flexible and cheaper than existing commercial solar cells.

Instead of using conventional sheets of silicon semiconductor the team created long thin silicon wires and embedded them in a polymer substrate - rather like spaghetti placed vertically inside a gelatine solution and left to set. Such a silicon-wire array has proved to be highly efficient at absorbing sunlight. Absorbing 85% of all collectible sunlight, it is the most efficient solar cell microstructure to date.

"These solar cells have, for the first time, surpassed the conventional light-trapping limit for absorbing materials," says Harry Atwater, professor and director of Caltech's Resnick Institute, which focuses on sustainability research.

One of the limitations of current solar cells is that some of the incident sunlight is scattered off the silicon wafer, essentially bouncing off the material rather than interacting with an electron inside. In this new silicon wire array much of the scattered light from one silicon strand is then absorbed by a nearby strand, hence the significant increase in absorption.

But the really important thing is that such absorbed light is actually useful in generating electricity. In order for that to happen a photon of light must interact with an electron thereby creating a charge carrier which is the source of an electric current. This array is able to convert a staggering 90-100% of incident photons into charge carriers.

"It's an important advance." says Atwater, modestly, and all the more impressive in that this is not the development of a new material as such but an ingenious use of existing materials into a novel structure. And, if being so highly efficient wasn't enough, these solar cells are also likely to be flexible and cheaper than existing flat solar cells. The polymer sheet makes the material flexible which means it can be manufactured as a huge roll, making it a much cheaper process than manufacturing brittle flat sheets.

It always seems as if solar power is about to become ubiquitous and yet it never quite happens. Hopefully, it won't be long before our buildings are gift-wrapped in a layer of super-efficient solar cells.
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