MIT researchers report fabricating one of the thinnest and lightest complete solar cells ever produced. To demonstrate how lightweight the cells are, a working cell was draped on top of a soap bubble.

MIT researchers place a lightweight solar cell on top of a soap bubble. Image source: Joel Jean and Anna Osherov.

A single process is used to manufacture the solar cell, the supporting substrate and a protective coating to shield it from the environment. The polymer parylene served as both the substrate and the coating in the proof-of-concept experiment. An organic material called DBP (tetraphenyldibenzoperiflanthene) was used as the primary light-absorbing layer. Parylene is a commercially available plastic coating commonly used 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 solvents. Established vapor deposition methods are applied to solar cell and substrate development.

The final solar cells, including substrate and coating, are one-fiftieth the thickness of a human hair and one-thousandth the thickness of equivalent cells on glass substrates — about two micrometers thick. Even so, they convert sunlight into electricity as efficiently as their glass-based counterparts, the researchers say.

The cells’ power-to-weight ratio is also claimed to rank among the highest ever achieved. A typical silicon-based solar module, whose weight is dominated by a glass cover, may produce about 15 W/kg of weight. The new cells have demonstrated an output of 6 W/g.

The cell may be too thin to be practical, the researchers say. But parylene films of thicknesses of up to 80 microns can be deposited using commercial equipment without losing the other benefits of in-line substrate formation.