In the quest for low cost solar cells, researchers have been diving into some strange new territory. The latest development comes courtesy of the University of Toronto, where researchers have cobbled together a contraption for spraying out solar cells. We’ve heard of spray-on solar cells before but the team, headed up by researcher Illan Kramer, has developed a new twist on the emerging technology.
From Junkyard Wars To Low Cost Solar Cells
Kramer is not shy about attributing the bones of the new low cost solar approach to a mashup between steampunk sensibility and reality entertainment:
This is something you can build in a Junkyard Wars fashion, which is basically how we did it. We think of this as a no-compromise solution for shifting from batch processing to roll-to-roll.
Specifically, Kramer and the team assembled their spray-on device with a spray nozzle from a steel mill (well, he didn’t really filch it from a steel mill, but he got one — they’re used for misting cool water over hot steel), and standard artists’ air brushes.
The low cost angle comes in when you compare the spray-on approach with the industry standard, batch processing.
Batch processing uses an assembly line sequence, which slows things down to a relative crawl. The spray-on approach is compatible with low cost solar cells based on thin film, which can be processed continuously using existing roll-to-roll technology.
That roll-to-roll manufacturing thing is critical to reducing costs. In terms of solar conversion efficiency, thin film and spray-on technology don’t come close to the gold standard, silicon. However, they could make up for it at the manufacturing end (the Obama Administration has launched a whole initiative called SolarMat to tackle manufacturing costs, but we digress).
This Is Not Your Father’s Spray-On Low Cost Solar Cell
The Toronto team is taking it up to the next level by using colloidal quantum dots as the basis for their spray-on technology. CQDs are nanoscale light-sensitive materials that are coming into use as a promising material for spray-on solar cells.
In an earlier paper published in the journal ACS Nano, Kramer and his team identified a significant obstacle in the path of deploying CQDs for low cost solar cell technology, and described a way to overcome it:
We diagnose the principal phenomenon—electronic states within the CQD film band gap that limit both current and voltage in devices—that must be cured…We close with a prescription, expressed as bounds on the density and energy of electronic states within the CQD film band gap, that should allow device efficiencies to rise to those required for the future of the solar energy field.
Another other obstacle is in the manufacturing process. Until now, CQDs have now been applied using expensive batch processing, not low cost roll-to-roll.
The team’s steampunk contraption enables a nanoscale mist of CQDs to be blasted directly onto a film as thin as plastic wrap. They team envision coating a film as flexible as plastic wrap, which could be applied to just about any oddly shaped surface including airplane wings, car body parts (like this!), and lawn furniture.
In a paper published just last month in ACS Nano, the team described how they’ve overcome the CQD quality problem as part of the spray-on solar cell approach. The problem was that the method of joining the CQDs in a film was based on replacing long aliphatic ligands (fancyspeak for an open chain of carbon atoms) with shorter ones, leading to a loss of efficiency. After nailing that down, the study went on to show how the undesired side effects can be “washed away:”
…by adding an acidic treatment during film processing, we can break up and wash away these complexes, producing a higher quality CQD solid. The improved material leads to photovoltaic devices with reduced series resistance and enhanced fill factor relative to controls employing previously reported CQD solids.
The rubber hits the road in the results, and so far they’re looking pretty good. The team has IBM’s BlueGene/Q supercomputer to demonstrate that their method — dubbed SprayLD — achieves solar conversion efficiencies as good as, or better than, their batch-processed cousins.
Look Out, Here Come The Attorney Generals!
Not for nothing, but while our friends up north are busy working on bringing next-generation low cost clean technology to Canada, down here in the US The New York Times has identified “at least a dozen” state Attorney Generals who have been using their offices to promote fossil fuel interests at the expense of new clean energy standards.
We’re not stewpid — everybody knows that legislators listen to lobbyists all the time, especially when it comes to energy issues (ALEC, much?) — but the Attorney General thing is new, and they’re being extra cute about it. As in, passing off an accusatory industry-written letter to the EPA as your own words cute.
So, stay tuned.
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