Roll-to-roll process improves viability of spray on solar cells

Illan Kramer and colleagues at the University of Toronto said they have made the breakthrough by devising a new way to spray solar cells onto flexible surfaces using miniscule, light-sensitive colloidal quantum dots (CQDs).

‘My dream is that one day you’ll have two technicians with Ghostbusters backpacks come to your house and spray your roof,’ said Kramer, a post-doctoral fellow with The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto and IBM Canada’s Research and Development Centre.

Solar-sensitive CQDs printed onto a flexible film could be used to coat many different surfaces. However, 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.

The SprayLD system sends 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.

According to the University, this roll-to-roll coating method makes incorporating solar cells into existing manufacturing processes much simpler. In two recent papers in the journals Advanced Materials and Applied Physics Letters, Kramer showed that the sprayLD method could be used on flexible materials without any major loss in solar-cell efficiency.

Kramer built his sprayLD device using parts that are readily available and affordable: he sourced a spray nozzle used in steel mills to cool steel with a fine mist of water, and a few regular air brushes from an art store.

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

‘As quantum dot solar technology advances rapidly in performance, it’s important to determine how to scale them and make this new class of solar technologies manufacturable,’ said Professor Ted Sargent, vice dean, research in the Faculty of Applied Science & Engineering at University of Toronto and Kramer’s supervisor. ‘We were thrilled when this attractively manufacturable spray-coating process also led to superior performance devices showing improved control and purity.’

In a third paper in the journal ACS Nano, 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.

The research was supported by the IBM Canada Research and Development Centre, and by King Abdullah University of Science and Technology.