MIT researchers claim to have built a laboratory proof-of-concept version of the thinnest, lightest solar cells for powering the next generation of portable electronic devices. The key for their innovation is to have the solar cell, the substrate that supports it, and a protective overcoating to shield it from the environment, all made in one growth process step.
“The innovative step is the realization that you can grow the substrate at the same time as you grow the device,” said MIT professor Vladimir Bulović. 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.
Unlike conventional solarcell manufacturing, which requires high temperatures and harsh chemicals, the new process takes place entirely in a vacuum chamber at room temperature, without the use of any solvents. Both the substrate and the solar cell are “grown” using established vapor deposition techniques.
The research team used a common flexible parylene polymer as both the substrate and the overcoating, and a DBP organic material as the primary light-absorbing layer. Parylene, a commercially available plastic coating, is widely used to protect implanted biomedical devices and printed circuit boards from environmental damage.
According to the researchers, different materials could be used for the substrate and encapsulation layers. Different types of thin-film solar cell materials, including quantum dots or perovskites, could also be substituted for the organic layers used in initial tests.
Parylene films with a thicknesses of up to 80 microns can be deposited easily using commercial equipment, without losing the other benefits of in-line substrate formation, the researchers said. Fabricating the cell entailed first depositing flexible parylene film one-tenth as thick as kitchen cling-wrap on a sturdier carrier material – in this case, glass.
The researchers lifted the entire parylene-solar cell-parylene stack off the carrier after the fabrication process was completed, using a frame made of flexible film. The final ultra-thin, flexible solar cells, which include substrate and overcoating are about two micrometers thick and convert sunlight into electricity just as efficiently as their glass-based counterparts, according to the researchers.
Whereas a typical silicon-based solar module, whose weight is dominated by a glass cover, may produce about 15 watts of power per kilogram of weight, the much lighter cells have already demonstrated an output of 6 watts per gram — about 400 times higher. “It could be so light that you don’t even know it’s there, on your shirt or on your notebook,” said Bulović. “These cells could simply be an add-on to existing structures.”
The new process is described in a paper in the journal Organic Electronics.