MIT engineers build portable, paper-thin solar cells

These durable, flexible solar cells, are much thinner than a human hair but can generate 18 times more power per kilogram than a conventional solar panel. 

The cells are made from semiconducting inks that can be easily printed. They are then glued to a strong, lightweight fabric, making them easy to install on any fixed surface, providing energy on the go as a wearable power fabric or even being rapidly deployed in remote locations for assistance in emergencies.

From boats to drones and mountain tents, the cells developed at the MIT could power almost any device in any location, with minimal installation needs. 

"The metrics used to evaluate a new solar cell technology are typically limited to their power conversion efficiency and their cost in dollars-per-watt. Just as important is integrability – the ease with which the new technology can be adapted," said Vladimir Bulović, senior author of a new paper describing the work.

"The lightweight solar fabrics enable integrability, providing impetus for the current work. We strive to accelerate solar adoption, given the present urgent need to deploy new carbon-free sources of energy."

Traditional silicon solar cells are fragile, so they must be encased in glass and packaged in heavy, thick aluminium framing, which limits where and how they can be deployed.

In order to increase access to solar energy, the team at MIT set out to develop thin-film solar cells that are entirely printable, using ink-based materials and scalable fabrication techniques.

To produce the solar cells, the researchers used printable electronic inks, deposited onto a prepared, releasable substrate that is only 3 microns thick. Using screen printing, an electrode is deposited on the structure to complete the solar module.

The researchers can then peel the printed module, which is about 15 microns in thickness, off the plastic substrate, forming an ultralight solar device.

Afterwards, the cells are attached with UV-curable glue to a fabric known as Dyneema, which weights only 13 grams per square metre. This material is so strong that it was used to make the ropes used to lift the sunken cruise ship Costa Concordia from the bottom of the Mediterranean Sea.

"While it might appear simpler to just print the solar cells directly on the fabric, this would limit the selection of possible fabrics or other receiving surfaces to the ones that are chemically and thermally compatible with all the processing steps needed to make the devices," said Mayuran Saravanapavanantham, another of the paper's authors.

"Our approach decouples the solar cell manufacturing from its final integration," 

When they tested the device, the MIT researchers found it could generate 730 watts of power per kilogram when freestanding and about 370 watts per kilogram if deployed on the high-strength Dyneema fabric, which is about 18 times more power per kilogram than conventional solar cells.

"A typical rooftop solar installation in Massachusetts is about 8,000 watts. To generate that same amount of power, our fabric photovoltaics would only add about 20 kilograms (44 pounds) to the roof of a house," Saravanapavanantham said. 

The researchers also tested the durability of their devices and found that, even after rolling and unrolling a fabric solar panel more than 500 times, the cells still retained more than 90 per cent of their initial power generation capabilities.

At the moment, the researchers are working on developing a material to protect the cells from being damaged by the weather and environment when deployed. 

"Encasing these solar cells in heavy glass, as is standard with the traditional silicon solar cells, would minimise the value of the present advancement, so the team is currently developing ultrathin packaging solutions that would only fractionally increase the weight of the present ultralight devices," said Jeremiah Mwaura, a member of the research team. 

The findings of the investigation were recently published in an article in the journal Small Methods.