November 11th, 2016 by Tina Casey
Unless President-elect Donald Trump shuts down all solar cell research programs everywhere, solar power is poised to inflict real pain on the fossil fuel industry. A case in point is the emerging field of perovskite solar cells, which are getting cheaper and more efficient practically by the minute.
In the latest development, a research team at the University of California – Berkeley has come up with a two-in-one perovskite solar cell that could push the efficiency envelope beyond anything on the market.
To be clear, there are no perovskite solar cells in commercial use today, but there will be, soon.
Perovskite refers to a class of synthetic materials that share the same crystalline structure as naturally occurring perovskite. They are cheap and easy to make, and they could offer a low-cost substitute for silicon in solar cells.
Here’s an explainer from Argonne National Laboratory:
…for technology made with perovskites — a class of materials causing quite a buzz in the solar research community — the energy payback time could be as quick as two to three months.
By this metric, perovskite modules are better than any solar technology that is commercially available today.
Argonne contrasts the 2-3 month turnaround with the 2-year payback typical of silicon solar cells.
Perovskite is also a hot topic because of the quick pace of improvement in solar conversion efficiency. Solar researchers have only been working on the material for a few years, and it’s already shot into the double-digit range.
That compares favorably with the decades-long process typical of other solar materials.
Of course, there is a hitch. Perovskites are notoriously unstable when exposed to water or humidity. In other words, they can’t be used outdoors — where solar cells need to be — until researchers come up with a way to shield them.
The UC-Berkeley Perovskite Solution
The UC-Berkeley team has come up with a double whammy. According to their calculations the new solar cell peaks out at an impressive 26% conversion efficiency, with a high of 21.7% and an average steady-state that clocks in at 18.4%.
That figure of 21.7% beats anything else in the perovskite field according to the Berkeley team. It also tops the efficiency of silicon devices currently on the market for home use and electronic devices.
The new solar cell is made like a “sandwich” with two different forms of perovskite interspersed among other layers. In previous attempts, two forms of perovskite have degraded each others’ performance, so the Berkeley team had to find a combo that works well together.
Here’s a schematic of the new solar cell:
And, here’s an explainer from the senior author of the study, UC physics professor Alex Zettl:
“Our architecture is a bit like building a quality automobile roadway. The graphene aerogel acts like the firm, crushed rock bottom layer or foundation, the two perovskite layers are like finer gravel and sand layers deposited on top of that, with the hexagonal boron nitride layer acting like a thin-sheet membrane between the gravel and sand that keeps the sand from diffusing into or mixing too much with the finer gravel. The gallium nitride layer serves as the top asphalt layer.”
The result is a solar cell that can harvest energy from the full solar spectrum, including invisible infrared light.
As for the moisture problem, the team has that covered:
“The perovskite/boron nitride sandwich is placed atop a lightweight aerogel of graphene that promotes the growth of finer-grained perovskite crystals, serves as a moisture barrier and helps stabilize charge transport though the solar cell.”
For more details check out the study in the journal Nature Materials.
Solar (And Shale Gas) Vs. Coal
Fossil industry stakeholders have blamed the US coal industry’s woes on the rise of solar and wind power under favorable Obama Administration policies. However, industry analysts agree that cheap natural gas has been the main factor pushing coal out of the marketplace.
That natural gas pressure is likely to continue increasing under President-elect Donald Trump. His leading advisor on energy policy is shale oil-and-gas tycoon Harold Hamm, who is rumored to be in line for the post of Energy Secretary.
The ongoing downward trend in solar (and wind) costs means that cheap renewables will become a threat to coal in their own right.
The Trump Administration could try to prop coal up by increasing subsidies, but that is highly unlikely. In addition to the Hamm factor, ExxonMobil has maneuvered itself into a prime position for leveraging the Paris climate agreement in favor of its recent shale gas investments.