Published on March 10th, 2017 | by Tina Casey0
Surprise! New 2-D Perovskite Solar Cell Exceeds Expectations For Solar Cell Efficiency
March 10th, 2017 by Tina Casey
The folks over at Los Alamos National Laboratory are taking a close look at Ruddlesden-Popper thin films for the next generation of low cost solar cells. Ruddlesden-Popper sounds like a character from a Monty Python skit, right? It refers to a 2-D, layered form of the crystalline material perovskite, which has become the focus of much excitement in the solar cell research field.
Ruddlesden-Popper thin films aren’t exactly spring chickens — they were first defined in 1957 — but the recent surge of interest in their application to the field of photovoltaics could be the final nail in the coffin for coal.
How Low Can Solar Go?
Researchers are excited about perovskites because they are relatively cheap and easy to manufacture, and they offer a relatively high conversion efficiency for the price (perovskites are synthetic versions of the naturally occurring mineral perovskite).
The cost of solar power is already down to parity with fossil fuels in some markets, and mass-produced perovskite photovoltaic cells could accelerate the downward trend.
Perovskites aren’t quite ready for their commercial closeup — they tend to fall apart in humid conditions, for one thing — but that hasn’t stopped researchers from exploring their game-changing potential.
“The 2D Hybrid Perovskites Continue To Surprise”
In the latest such development, the Los Alamos team practically ran out of words trying to describe the significance of their Ruddleson-Popper photovoltaic study. Here’s team member Mercouri Kanatzidis of Northwestern University enthusing over the results:
“The 2D hybrid perovskites continue to surprise. When we first designed these materials we were hoping that high quality samples of them would exhibit novel optoelectronic properties…Well, they have done so and then some. They have exceeded our expectations and are proving to be truly amazing systems. We have only scratched the surface of what is there—sorry for the pun—in this 2D family and we anticipate continued excitement going forward.”
If you are wondering what’s up with that pun about scratching the surface, Kanatzidis is referring to the focal point of the study.
One drawback of layered perovskites and similar photovoltaic materials is that their efficiency tends to degrade at edges and surfaces.
The Los Alamos team was able to show that such materials can be tweaked to avoid that problem.
The solution was to insert organic (think: plastic) layers between the perovskite layers.
Here’s a nifty schematic showing what’s at work:
And, here’s the explainer from Los Alamos. The yellow beam represents sunlight:
…Edge-states at the edges of the 2D perovskite layers lead to dissociation of electron-hole pairs (excitons) to free carriers for efficient photovoltaics of more than 12 percent (left). Dissociated carriers captured and located at the edge-states live longer while being protected from loss mechanisms (right), which results in efficient fluorescence of a few tens of percent applicable to next-generation LEDs. (top) Material structure sketching the stacking of nanometer-thick layers of 2D perovskite and organic spacing layers.
Let’s Hear It For The Free Flow Of Ideas
Considering the upheaval over US immigration and travel policy under the Trump Administration, it’s worth noting that the Los Alamos team is based partly in France. Along with the US Department of Energy (still alive and kicking!), France’s Cellule Energie du CNRS and University of Rennes also supported the project.
Here’s the rundown from Los Alamos on the team members (guess which ones can trace their US roots back to the Mayflower):
J.-C. Blancon, W. Nie, S. Tretiak, J. J. Crochet and A. D. Mohite of Los Alamos National Laboratory; H. Tsai and P. M. Ajayan of Rice University, Houston, Texas; C. C. Stoumpos, C. M. M. Soe, and M. G. Kanatzidis of Northwestern University, Evanston, Illinois; L. Pedesseau and J. Even of Fonctions Optiques pour les Technologies de l’Information (FOTON), INSA de Rennes, France; C. Katan and M. Kepenekian of Institut des Sciences Chimiques de Rennes (ISCR), Université de Rennes, France; K. Appavoo and M. Y. Sfeir of Brookhaven National Laboratory, Upton, New York.
Clock Running Down On Oil…And Natural Gas, Too
You can get the full rundown on the new perovskite research from the journal Science under the title, “Extremely efficient internal exciton dissociation through edge states in layered 2D perovskites.“
For those of you on the go, the takeaway is that the new research provides a precise definition of the forces at play in 2-D photovoltaics. That, in turn, provides the photovoltaic field with more efficient pathway for designing low cost, high efficiency solar cells.
That’s not particularly great news for oil companies like ExxonMobil. As with other major oil producers, ExxonMobil has been ramping up its natural gas operations as it pivots into out of petroleum dependency and into a more diverse energy portfolio.
ExxonMobil and other oil-dependent energy companies have seen the writing on the wall. Low cost solar and other renewables are bottling up the potential for future oil growth in some important markets, including the diesel generator field. Oil is especially vulnerable when it comes to the wide-open off grid market in Africa and other emerging economies.
So, oil companies are looking to their natural gas operations for long term market growth. That’s been the main driver forcing coal out of the power generating market in the US and elsewhere.
That long term outlook could turn into short term. If perovskite researchers can resolve some shortcomings with the finicky material, natural gas will be next on the fossil fuel chopping block.
Other factors tamping down the demand for oil and natural gas are rapid growth in the EV market, the advent of “green chemicals” (sustainable alternatives to petrochemicals) and the emergence of renewable sources for hydrogen fuel.
These forces will continue to gain strength as the age of fossil fuels draws to a close, hopefully sooner rather than later.
Images: via Los Alamos National Laboratory.