Published on September 22nd, 2016 | by Tina Casey0
Columbia Scientists Unlock Big Perovskite Solar Cell Mystery
September 22nd, 2016 by Tina Casey
Perovskites have been tapped as the new “superstar” material in the race for more efficient, less expensive solar cells, and a team of researchers at Columbia University has just figured out why they perform so well. The discovery could also help overcome a major hurdle between perovskite solar cells and the mass market.
What’s So Great About Perovskite Solar Cells?
The new Columbia study has to do with a class of solar cell materials called hybrid organic inorganic perovskites (HOIPs). The research team calls attention to something that caught the CleanTechnica eye a couple of years ago (and our sister site PlanetSave, which is the astonishing pace of improvement in perovskite solar cell technology within just the past few years (perovskites are a class of synthetic materials based on the structure of naturally occurring mineral perovskite).
The perovskite track record is particularly impressive when compared to the rate of improvement for silicon, which is the current gold standard for solar cell technology. This is how the Columbia researchers describe it:
Over the last seven years, scientists have managed to increase the efficiency with which HOIPs can convert solar energy into electricity, to 22 percent from 4 percent. By contrast, it took researchers more than six decades to create silicon cells and bring them to their current level, and even now silicon cells can convert no more than about 25 percent of the sun’s energy into electrical current.
Don’t just take their word for it. The National Renewable Energy Laboratory is also impressed with the pace of perovskite solar cell research. The lab had this to say back in 2014:
A new solar material that has the same crystal structure as a mineral first found in the Ural Mountains in 1839 is shooting up the efficiency charts faster than almost anything researchers have seen before—and it is generating optimism that a less expensive way of using sunlight to generate electricity may be in our planet’s future.
The Perovskite Solar Cell Mystery
One key obstacle to low-cost silicon solar cells is the fact that silicon needs to be practically flawless in order to function efficiently. Nanoscale defects at the ion level can make sunlight dissipate before it is transformed into a current.
In contrast, perovskites can operate at a high level of efficiency even with numerous defects. That’s a good thing to have when you’re gunning for a high throughput, low cost manufacturing process.
So, for example, you could potentially come up with a reasonably efficient perovskite solar cell by using established, room temperature solution-based processes.
The question, until now, is why can perovskite crystals still perform well, even when loaded with defects.
The answer, according to the Columbia research team, is that the rate of energy loss is reduced by more than three orders of magnitude in HOIPs. In effect, electrons “avoid bumping into” the numerous defects that occur in perovskite solar cells that are made using relatively inexpensive methods.
Getting The Lead Out
The Columbia study could also help to chart a path toward overcoming one very concerning characteristic of perovskite solar cells, namely, their reliance on lead.
Now that the mechanism behind the high efficiency/low cost equation has been explained, it is possible to mimic those characteristics using non-toxic materials.
Columbia professor Xiaoyang Zhu, who leads the research team, foresees a collaboration with his colleagues on designing and fabricating just such materials, so stay tuned for that.
Image: Perovskite solar cell material by Nicoletta Barolini via Columbia University.