Published on January 18th, 2018 | by Tina Casey0
New Perovskite Solar Cell Breakthrough Funded By Texas Oilman’s Legacy
January 18th, 2018 by Tina Casey
The cost of solar power has been shooting downward with no end in sight, and a good deal of the excitement moving forward has to do with perovskite. The material is super efficient from a solar energy conversion point of view, and it’s super cheap to make, but it is also super allergic to life. Researchers have been going nuts trying to figure out how to keep perovskite from degrading in real world conditions, and now a US team has a bead on the solution.
No, Really, How Low Can Solar Go?
CleanTechnica has spilled a lot of ink on the downward spiral of costs in the solar power field. “Soft” costs like zoning and permitting factor in heavily, but from a technology perspective the exciting stuff inhabits the realm of hard costs, namely, squeezing the maximum conversion efficiency out of the least expensive materials.
Perovskite certainly fits the bill. Naturally occurring perovskite was discovered in the Ural mountains in the 19th century. More recently, photovoltaic researchers discovered that its unique crystalline structure could be easily — and inexpensively — replicated in the lab.
Getting the stuff to behave is a whole ‘nother can of worms, and that’s where the new research comes in.
A Carrot For The Perovskite Solar Cell Unicorn
Here in the US, the National Renewable Energy Laboratory has emerged as perovskite cheerleader #1. They are really enthused about their latest research, conducted with the University of Texas at Austin.
The new perovskite research pinpoints, for the first time, exactly where the degradation process kicks off — and it’s not the usual suspect.
Until now, the finger of blame was pointing at something called grain boundaries. Here’s the explainer from NREL:
Perovskite solar cells possess a polycrystalline structure with individual crystals grains. These grains are adjacent to other crystals and the area where the crystals touch is known as a grain boundary.
In other words, previous research seemed to show that the visible boundaries between grains were at fault. The NREL research revealed that the surface of each grain is the real culprit.
The team deployed a new super power/new piece of equipment called light-stimulated microwave impedance microscopy to map the conversion efficiency of solar cells on the nanoscale.
The rest sounds easy enough. Working with two samples, the team tracked the loss of conversion efficiency over a period of one week. The samples were coated with an acrylic glass (like Plexiglas), which protected them from ambient humidity for the first few days.
After the humidity penetrated the coating, the conversion efficiency went down. Here’s another NREL explainer:
The drop in the photoconductivity emerged from the disintegration of the grains and not from the grain boundaries, the research found. In this instance, the scientists noted, the grain boundaries “are relatively benign” and determined perovskite films with better crystallinity should be a direction of future research for improving perovskite solar cell performance and durability.
That’s “better” as in bigger crystals. Of the two samples used in the study, one had smaller grains and a conversion efficiency of 15%, and the other had larger grains and a conversion efficiency of 18%.
Here’s a snippet from the study:
Surprisingly, the GBs [grain boundaries] exhibit photo-responses comparable to the grains, and they are not the nucleation centers for the degradation process. Our results highlight the unique defect structures responsible for the remarkable performance of PSC devices, and address the significance of crystallinity to further improve their energy conversion efficiency.
Want more? Check out “Impact of Grain Boundaries on Efficiency and Stability of Organic-Inorganic Trihalide Perovskites” in the journal Nature Communications.
The research is also important because it validates the use of light-stimulated microwave impedance microscopy in solar cell research.
Shoutout to study co-authors and researchers Zhaodong Chu, Mengjin Yang, Philip Schulz, Di Wu, Xin Ma, Edward Seifert, Liuyang Sun, Xiaoqin Li, Kai Zhu, and Keji Lai.
What Is The Welch Foundation?
So, here’s where it gets interesting. The research was partly funded by the US Department of Energy (group hug, taxpayers!), the National Science Foundation, and the Welch Foundation, which is this:
The Welch Foundation, based in Houston, Texas, is one of the United States’ largest private funding sources for basic chemical research.
Ya don’t say? The Welch Foundation was established in 1954 through the beneficence of Robert Alonzo Welch, who is described as “a self-made man with a strong sense of responsibility to humankind, an enthusiastic respect for chemistry and a deep love for his adopted state of Texas.”
Welch worked up a fortune in oil and minerals, and the Foundation is focused on supporting Texas-based scientists, so it’s not surprising that the petrochemical industry has been a focus of the largess.
One recent example is a $4 million grant awarded to the University of Houston in 2013, to foster development of the gas-to-plastics industry. The grant was made in light of the US shale gas boom, so there’s that.
On the other hand, the Foundation has been moving into the decarbonization area.
This fall, for example, there is the 2018 Welch Conference on Chemical Research,”Water: Science and Technology.” The conference includes a session on sustainability:
We have many pressing global problems involving water, from water availability and treatment for personal use and agriculture, to the need for carbon-neutral energy sources. Speakers in this session will discuss water-related catalysis for solar fuels, and separation science.
The Welch Foundation is also behind a 2012 Rice University study on carbon nanotubes, a 2014 Rice University study on “black silicon” photovoltaic cells aimed at driving costs down, and a 2014 solar cell study at the University of Houston that charts a path for developing more efficient solar conversion materials.
The oil industry (well, with one notable exception) is finally beginning to pivot out of carbon and into renewable energy and electric vehicles, so stay tuned for more news on that score from private funding sources like the Welch Foundation.
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Image (screenshot): “Illustration shows the microwave impedance microscopy technique illuminating the solar cell from below”via University of Texas at Austin.
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