So…now that the US has busted out of the Paris climate accord, what comes next for the US Energy Department? Despite President Trump’s pro-coal rhetoric, Energy Secretary Rick Perry has spent his tenure pitching wind and solar like it’s going out of business — and that could happen to his agency if the President’s proposed budget cuts go through.
In the meantime, let’s see if Perry can keep the stream of good news humming along, Paris or not. So far so good: yesterday the Energy Department’s Ames National Laboratory had some good news to report about one of CleanTechnica’s favorite topics, “coal killing” organometal halide perovskite solar cells.
Coal-Killing Perovskite Solar Cells
For those of you new to the topic, perovskites belong to a class of synthetic crystals based on the structure of naturally occurring perovskite.
When used in solar cells, perovskites are combined with carbon-based molecules, a metal (typically lead, though some researchers are exploring tin), and a halide (iodide is one example), thus the name organometal halide perovskites.
Perovskites popped up in the photovoltaic research field just a few years ago, but they have lit a fire under scientists all over the globe because they promise high efficiency at low cost.
Coal is already under siege from cheap natural gas, and the cost of renewable energy is sinking rapidly. Researchers have high expectations that perovskites will be the game-changer that pushes the cost of solar off a cliff, putting even more pressure on the beleaguered coal industry.
The Energy Department’s National Renewable Energy has charted the progress of perovskite research and it’s on the fast track. According to NREL, researchers teased an initial conversion efficiency of 3.8% up to more than 16% in just five years, from 2009 to 2014.
New research shows the trend continuing, with a record of 22.1% conversion efficiency cited in a study published last March.
The catch — and there is always a catch — is that perovskites are unstable outside of the laboratory. Compared to the quarter-century of life expected from silicon solar cells, perovskite solar cells only last a few months.
Understanding how and why perovskites do what they do is a fundamental first step toward deploying the material in the real world, and it looks like Ames has hit a breakthrough with its new perovskite research.
Caught In The Act
In their new study, the Ames team aimed to define the pivotal process involved in solar energy conversion, namely, how pairs of electrons and “holes” called excitons form and un-form, and how to define the event in terms of time lapse and quantum pathways.
Here’s Ames scientist Jigang Wang enthusing over the implications for catapulting perovskite research into the commercial sphere:
“If you look at the natural process, in photosynthesis, it’s an extremely efficient process in some biological molecules, so it’s also very coherent…If we can measure such a memory in the charge transport and energy migration in these materials, we can understand and control it, and have the potential to improve them by learning from Mother Nature.”
Conventional measurement devices don’t work at the scale needed for the Ames research, so they deployed this:
Ultrafast terahertz spectroscopy techniques provided a contactless probe that was able to follow their internal structures, and quantify the photon-to-exciton event with time resolution better than one trillionth of a second.
You can get all the details from the study “Ultrafast terahertz snapshots of excitonic Rydberg states and electronic coherence in an organometal halide perovskite” in the journal Nature Communications.
For those of you on the go, here’s a snippet from the abstract that defines the unique characteristics of perovskites compared to other solar cell materials:
The nearly ∼1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ∼13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors.
Got all that?
Why A National Laboratory
Considering that the Energy Department is fighting for its life, the folks at Ames did not pass up a chance to make a pitch for survival.
In the press release announcing the new research, Wang noted that the effort was a collaborative one drawing from multiple specialists at the lab, with resources that would be difficult if not impossible for the private sector to assemble:
“This was only possible with the collaboration of experts in material design and fabrication, computational theory, and spectroscopy…Having those capabilities in one place is what makes Ames Laboratory one of the most forward looking places in this kind of photonic materials research.”
As for whether or not anybody is listening over there at 1600 Pennsylvania Avenue, the Paris debacle indicates not.
Nevertheless, in the spirit of collaboration here’s a shoutout to the authors of the new perovskite study, Liang Luo, Long Men, Zhaoyu Liu, Yaroslav Mudryk, Xin Zhao, Yongxin Yao, Joong M. Park, Ruth Shinar, Joseph Shinar, Kai-Ming Ho, Ilias E. Perakis, and Javier Vela along with Jigang Wang.
Image: via Ames National Laboratory, “(a) The THz response functions (red dots) measured under 790 nm wavelength and 550 μJ cm−2 fluence, at T=8 K and pump probe delay Δt=60 ps…” (full caption available via Nature Communications).