Scientists from Sandia National Laboratories have developed tiny, glitter-sized photovoltaic cells that are ten times thinner than conventional solar cells and could one day be used in a variety of applications – from satellites and remote-sensing, to tents and perhaps even clothing. Yep, these cells could turn the average Joe into a walking solar-battery charger.

The Sandia research team identified over 20 benefits of scale for these tiny cells over traditional solar cells, including better performance, more efficiencies and possibly reduced costs. Sandia lead investigator, Greg Nielson said, “Eventually units could be mass-produced and wrapped around unusual shapes for building-integrated solar, tents and maybe even clothing,” he said. This would make it possible for hunters, hikers or military personnel in the field to recharge batteries for phones, cameras and other electronic devices as they walk or rest.”

While solar-charged clothing is not a particularly new concept, these solar particles - made from crystalline silicon – are expected to have more applications, be less expensive and have greater efficiencies than the photovoltaic cells made from six-inch square solar cells. In addition, the team believes that the modules made from the photovoltaic cells could have intelligent controls, inverters and storage integrated at the chip level. An integrated module such as this could reduce problems such as cumbersome design and grid integration processes currently experienced by solar technical assistance teams.

Cheap as chips

The cost reduction is due partly to the fact the microcells don’t need a lot of material to become highly efficient and well-controlled devices. They are just 14 to 20 micrometers thick - a human hair is approximately 70 micrometers thick – and are ten times thinner than a conventional 6 x 6 inch solar cell, however they are capable of being used in large-scale power production. This could mean a reduction in the manufacturing and installation costs when compared to current photovoltaic techniques.

Sandia researcher, Murat Okandan, said, “So they use 100 times less silicon to generate the same amount of electricity. Since they are much smaller and have fewer mechanical deformations for a given environment than the conventional cells, they may also be more reliable over the long term.”

Using a commercial machine called a pick-and-place, up to 130,000 pieces of glitter can be placed per hour at electrical contact points pre-established on the substrate. The cost is estimated at one-tenth of a cent per piece and it is expected each module will contain 10,000 to 50,000 cells per meter – depending on the level of optical concentration required.

Low cost solar concentrators can be placed over each cell which will increase the number of photons being converted into electrons via the photovoltaic effect. And although the cells are small they have a high voltage output which will reduce the costs associated with wiring.

Smaller can sometimes be better

As the cells are so small, they can be manufactured from commercial wafers of any size and if one cell is defunct, it can simply be replaced rather than having to replace an entire brick-sized unit. These small cells have individualized wiring, eliminating the need for thicker power lines to cope with the increased power. There is also less of an issue with shading from overhead obstructions. “The shade tolerance of our units to overhead obstructions is better than conventional PV panels,” said Nielson, “because portions of our units not in shade will keep sending out electricity where a partially shaded conventional panel may turn off entirely.”

Change is good

Although there is a huge change from manufacturing conventional silicon wafers to manufacturing microscale PV cells, the team believes the process would be relatively straightforward because they would use the techniques used in microelectromechanical systems (MEMS), electronics and LED industries.

The cells will be formed on silicon wafers, etched and produced in a hexagonal shape with electrical contacts contained on each shape. At this stage, electricity can be harvested at a rate of 14.9 percent efficiency from the cells – this compares favorably with commercial modules which have a range of 13 to 20 percent efficiency.

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