Published on July 3rd, 2015 | by Tina Casey28
Perovskites Will Power New Low-Cost & Highly Efficient Solar Cells
July 3rd, 2015 by Tina Casey
Since we’re celebrating Independence Day this weekend over here in the USA, we’re sharing this fireworksy image of perovskite crystals emailed to us by the folks at Los Alamos National Laboratory. Better known for its work on nukes, the lab has been hot on the trail of next-generation, super-efficient solar cells, and it looks like perovskite is the name of the game, partly because they are “more than a thousand times” less expensive than those fancy multi-junction solar cells.
First, The Bad News About Perovskite Solar Cells
For those of you new to the topic, perovskites refer to a class of earth-hued minerals first discovered in the 19th century in the Ural Mountains by Gustav Rose and named after the Russian mineralogist Lev Perovsky, which accounts for the Russian sounding name.
Perovskites are easily synthesized, and their distinctive crystalline structure makes them a perfect match for the development of efficient solar cells that can beat the current gold standard, which is silicon.
Perovskites may also play a role in next-generation electric vehicle batteries, according to some interesting maneuvers recently undertaken by Volkswagen.
Where were we, though? Oh, right, efficient solar cells. Perovskites look good as far as efficiency goes, but they tend to burn the candle at both ends. In other words, they are unstable. Like the rest of us, perovskites can take the heat but not the humidity, and they tend to fall apart in damp conditions.
In addition, until recently, perovskites were considered more expensive than other materials for commercial solar cells.
The Good News About Perovskite Solar Cells
Aside from being easily synthesized, perovskites are known to be easy to work with (that’s probably a dig at graphene, but whatever).
More to the point, despite the humidity thing, the research is rapidly advancing toward the design of a perovskite-based solar cell that provides stability with efficiency, as well as low cost.
One such advance consists of ditching lead, a toxic material used in conventional perovskite solar cells, and substituting low-cost, non-toxic materials. Alternatively, lead-based perovskite solar cells could provide a safe way to re-use lead from spent lead-acid batteries….
Coming up with a low-cost, low-energy manufacturing process is also critical for commercialization.
Combining perovskite technology with silicon is another path to next-generation efficient solar cells.
Even Better News
You can see elements of these approaches, and more, coming together in the perovskite research being conducted at Los Alamos National Laboratory (LANL), so if you’re in the mood for a long-form article, we do encourage you to check out the lab’s “Perovskite Power” article, published just last week.
The lab has come up with a reliable “recipe” for producing perovskite crystals that approach silicon in terms of solar conversion efficiency.
By reliable, the lab doesn’t mean defect-free, and that’s a critical point.
At first glance, perovskite crystals are inferior to silicon because of their relatively wide band gap (band gap is shorthand for how far electrons have to travel). However, LANL put that inferior characteristic to work, and developed a solar cell in which electrons bounce back and forth multiple times in a perfectly formed area, with only an extremely rare chance of venturing into an area of defect.
Here’s the happy recap from LANL:
As a result, the perovskite, while slightly worse than silicon in terms of its natural band gap, can be much more cheaply manufactured with excellent crystal purity.
The LANL secret sauce is a “hot casting” manufacturing process, in which a substrate is first heated, then coated with a solution containing perovskite crystals. While the process does require some energy input, it is a big improvement over conventional high-heat methods:
Unlike the complex crystal-growth methodologies used to make conventional, state-of-the-art semiconductor solar cells, solution processing is both fast and flexible. Fast means inexpensive, and the flexibility of liquid solution-based processing means the perovskite can be applied in convenient ways, such as spraying or painting the photoelectric layer directly onto a surface, opening the door to numerous new applications.
As for performance, in just six months, the lab has achieved an average of 15% conversion efficiency for its perovskite solar cells, topping out at 18%.
In contrast, LANL notes that after literally decades of research, conventional silicon solar cells in commercial use have reached about 20% conversion efficiency compared to the theoretical maximum of 33%. Multi-junction solar cells (multi-junction is fancyspeak for the use of multiple materials layered on top of each other) can reach 40%, but — here’s that money quote — perovskites are “more than a thousand times less expensive.”
Next steps for LANL include concentrating on beating silicon solar cell efficiency by subbing in a more tailored form of perovskite for the “generic” form used in the research, fine-tuning the manufacturing process, and developing more effective materials for the electrodes.
The big hitch is the aforementioned stability issue, and if LANL can’t quite crack that nut on its own, other up-and-coming perovskite research (here’s another example) indicates that solutions are close at hand.
Image: High efficiency perovskite crystals courtesy of LANL.
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