Spray-on solar power

Ilan Kramer shows off his spray-on solar cell kit.
PHOTO: UNIVERSITY OF TORONTO

Ilan Kramer hopes powering your tablet will be as simple as wrapping it in cling wrap.

The post-doctoral fellow, his colleagues at the Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto and IBM Canada’s Research and Development Centre have invented a way to spray solar cells onto flexible surfaces, a major step toward making spray-on solar cells easy and cheap to manufacture.

Light-sensitive materials called colloidal quantum dots (CQDs) printed onto a flexible film would coat weirdly shaped surfaces, such as patio furniture or an airplane’s wing.

A surface the size of your car’s roof wrapped with CQD-coated film would produce enough energy to power three 100-watt light bulbs, or 24 compact fluorescents.

Kramer’s sprayLD system – a play on the manufacturing process called ALD (atomic layer deposition) – involves materials that are laid down on a surface one atom-thickness at a time.

Until now, it was only possible to incorporate light-sensitive CQDs onto surfaces through batch processing, which is an inefficient, slow and expensive assembly-line approach to chemical coating.

SprayLD blasts a liquid containing CQDs directly onto flexible surfaces, such as film or plastic, like printing a newspaper by applying ink onto a roll of paper. This roll-to-roll coating method makes incorporating solar cells into existing manufacturing processes much simpler.

No-compromise solution
Kramer built his sprayLD device using parts that are readily available and rather affordable, sourcing a spray nozzle used in steel mills to cool steel with a fine mist of water, and a few regular airbrushes from an art store.

“This is something you can build in a Junkyard Wars fashion, which is basically how we did it,” says Kramer. “We think of this as a no-compromise solution for shifting from batch processing to roll-to-roll.”

In two recent research papers in Advanced Materials and Applied Physics Letters, Kramer showed that the sprayLD method can be used on flexible materials without any major loss in solar-cell efficiency.

A third paper in the journal ACS Nano demonstrated how Kramer and his colleagues used IBM’s BlueGeneQ supercomputer to model how and why the sprayed CQDs perform just as well as – and in some cases better than – their batch-processed counterparts.
And he has ambitious plans for his technology.

“My dream is that one day you’ll have two technicians with Ghostbusters backpacks come to your house and spray your roof.”

This article appears in the Jan./Feb. 2015 issue of PLANT.