By Tina Casey in Clean Technica, 17 April 2017
Thin Film Solar Cells Are Coming On Strong
Thin film solar cells are generally not as efficient as conventional silicon solar cells, but they do possess several key advantages that can counterbalance that shortcoming. Thin film solar cells can be manufactured at high speed and at high volume, using roll-to-roll processes similar those used in industry for decades.
They are also relatively lightweight and flexible, which means they don’t have to be planted on a rooftop or stuck on a pole out in a field to be useful. Thin film solar cells can be integrated into building elements and moving vehicles, among many other applications.
The Perovskite Problem
To amp up the cost advantage of thin film, researchers have been checking out a class of low cost, synthetic crystalline material called perovskites.
Perovskites are based on the natural mineral perovskite. They burst on the scene just a few years ago when researchers discovered their solar-friendly properties. Since, then labs around the world have coaxed the efficiency level of perovskite solar cells up at an exponential rate.
NREL is one of those labs focusing on perovskites, and it has been working through several pesky problems that blocked the material from commercial application.
The new perovskite research tackles an issue relating to the potential for high volume, thin film perovskite solar cell production.
The conventional method for creating perovskite solar cells in the lab is to “grow” the crystalline structure, using a process called spin coating. Spin coating yields a high quality product, but it does not lend itself to the kind of scaled-up activity required for low cost manufacturing.
Spin coating is a complex process and NREL researchers spotted one especially weak link:
One extremely critical stage requires the addition of an antisolvent that extracts the precursor chemicals, and thus create crystals of good quality. The window for this step opens and closes within seconds, which is detrimental for manufacturing due to the precision required to make this time window.
Solving The Perovskite Problem
The NREL team figured out a way to pry that “window” open wide enough to allow for a high volume manufacturing process.
Since the March for Science is coming up soon let’s give them all a shoutout:
Kai Zhu, a senior scientist in NREL’s Chemistry and Nanoscience Center, is lead author. The co-authors are Mengjin Yang, Zhen Li, Matthew Reese, Obadiah Reid, Dong Hoe Kim, Sebastian Siol, Talysa Klein, Joseph Berry, and Michael van Hest from NREL, and Yanfa Yan from the University of Toledo.
You can get all the details from the journal Nature under the title, “Perovskite ink with wide processing window for scalable high-efficiency solar cells.”
Here’s a juicy bit from the abstract:
Here we demonstrate a chlorine-containing methylammonium lead iodide precursor formulation along with solvent tuning to enable a wide precursor-processing window (up to ∼8 min) and a rapid grain growth rate (as short as ∼1 min).
Did you get all that?
According to the team, the same formula performed equally well regardless of whether it was applied using spin coating or blade coating (blade coating is the one that enables high volume production).
The team reports a conversion efficiency of 13.3 percent for a four-cell module.
The whole module was less than 13 square centimeters so it looks like there’s a way to go before the new solar cell comes to a rooftop near you, but if Perry can convince the Trump Administration to spare the Energy Department from the budget axe, the team will get a chance to refine their work.
The new perovskite research is just one example of low cost solar research coming your way under the Trump Administration. Last alone year the Energy Department funded 10 innovative projects aimed at undercutting the fossil fuel market with new high performance, low cost solar cells.
Good luck with that budget thing, Rick Perry!
Photo (cropped): solar cells “grown” from perovskite ink by Dennis Schroeder.