Solar cells are getting seriously light

Researchers continue to break new ground with advances in solar cell technology that uses organic polymer material rather than silicon as the light absorbing layer.

Last month, Cosmos reported on a German team’s success producing power in space with a new design for hybrid perovskite and organic solar cells.

Now, a team from Saudi Arabia’s King Abdullah University of Science and Technology reports that it has used inkjet printing to create organic cells so light and flexible they can rest on a soap bubble.

Solar cells are typically made by spin-coating or thermal evaporation, which involves using a transparent and conductive material called indium tin oxide (ITO) as an electrode.

However, ITO is brittle and inflexible so the technique isn’t scalable, says Eloïse Bihar, lead author of a paper in the journal Advanced Materials.

That’s where inkjet printing comes into play.

Bihar and colleagues printed a transparent, conductive polymer called PEDOT:PSS. The electrode layers sandwiched a light-capturing organic photovoltaic material. The entire device could then be sealed in a flexible and waterproof protective coating of a polymer named parylene.

Inkjet printing is commonplace, but the challenge was to develop a functional ink that could be used on such tiny panels.

“Inkjet printing is a science on its own,” says co-author Daniel Corzo. “The intermolecular forces within the cartridge and the ink need to be overcome to eject very fine droplets from the very small nozzle.

“Solvents also play an important role once the ink is deposited because the drying behaviour affects the film quality.”

After optimising the ink composition for each layer of the device, the solar cells were printed onto glass to test their performance.

The researchers say they achieved a power conversion efficiency (PCE) of 4.73%, beating the previous record of 4.1% for a fully printed cell. They also showed they could print a cell onto an ultrathin flexible substrate, reaching a PCE of 3.6%.