Thinnest, lightest solar cells ever made

Thinnest, lightest solar cells ever made

Researchers at MIT have demonstrated a technology of making thin solar cells that can be placed on a hat, a shirt and more. Though it may take years to develop into a commercial product, the laboratory proof-of-concept shows a new approach to making solar cells that could help power the next generation of portable electronic devices.

The new process is described in a paper by MIT professor Vladimir Bulovi, research scientist Annie Wang, and doctoral student Joel Jean, in the journal Organic Electronics.

MIT had earlier made an attempt to develop thin solar panels. Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering at MIT, stated earlier that the previous approach pushed towards the ultimate power conversion possible from a material for solar power. It s 20 to 50 times thinner than the thinnest solar cell that can be made today, Grossman adds. You couldn t make a solar cell any thinner. This slenderness is not only advantageous in shipping, but also in ease of mounting solar panels.

Bulovi, MIT's associate dean for innovation and the Fariborz Maseeh (1990) Professor of Emerging Technology, says the key to the new approach is to make the solar cell, the substrate that supports it, and a protective overcoating to shield it from the environment, all in one process. The substrate is made in place and never needs to be handled, cleaned, or removed from the vacuum during fabrication, thus minimizing exposure to dust or other contaminants that could degrade the cell's performance.

In this initial proof-of-concept experiment, the team used a common flexible polymer called parylene as both the substrate and the overcoating, and an organic material called DBP as the primary light-absorbing layer.

Parylene is a commercially available plastic coating used widely to protect implanted biomedical devices and printed circuit boards from environmental damage. The entire process takes place in a vacuum chamber at room temperature and without the use of any solvents, unlike conventional solar-cell manufacturing, which requires high temperatures and harsh chemicals. In this case, both the substrate and the solar cell are grown using established vapor deposition techniques.

The team emphasizes that these particular choices of materials were just examples, and that it is the in-line substrate manufacturing process that is the key innovation. Different materials could be used for the substrate and encapsulation layers, and different types of thin-film solar cell materials, including quantum dots or perovskites, could be substituted for the organic layers used in initial tests.

But already, the team has achieved the thinnest and lightest complete solar cells ever made, they say. To demonstrate just how thin and lightweight the cells are, the researchers draped a working cell on top of a soap bubble, without popping the bubble. The researchers acknowledge that this cell may be too thin to be practical -- If you breathe too hard, you might blow it away, says Jean -- but parylene films of thicknesses of up to 80 microns can be deposited easily using commercial equipment, without losing the other benefits of in-line substrate formation.

A flexible parylene film, similar to kitchen cling-wrap but only one-tenth as thick, is first deposited on a sturdier carrier material - in this case, glass.

We put our carrier in a vacuum system, then we deposit everything else on top of it, and then peel the whole thing off, explains Wang. Bulovi says that like most new inventions, it all sounds very simple -- once it's been done. But actually developing the techniques to make the process work required years of effort.

While the solar cell in this demonstration device is not especially efficient, because of its low weight, its power-to-weight ratio is among the highest ever achieved.

It could be so light that you don't even know it's there, on your shirt or on your notebook, Bulovi says. These cells could simply be an add-on to existing structures.

Still, this is early, laboratory-scale work, and developing it into a manufacturable product will take time, the team says.

Thinnest, lightest solar cells ever made