Weren’t we just saying that perovskite solar cells are the next big thing? Well, make that tin perovskite solar cells. Tin perovskite solar cells are suddenly a thing this week, with not one but two major new research announcements coming out of the US and the UK.
The significance is not so much in the tin perovskite cells’ conversion efficiency, which is laughably low compared to other solar hot rods on the market. It’s their potential for commercializing super cheap solar cells. Tin is an inexpensive, abundant material and its use in solar cells would drive costs down while alleviating the kind of geopolitical supply chain issues that bedevil other solar cell materials.
Tin also has the advantage of being easier on public health and the environment than lead, which is the conventional alternative for perovskite solar cells.
Tin Perovskite Solar Cells From The US
Perovskite solar cells just sailed across CleanTechnica’s radar a couple of weeks ago. Perovskite refers to a mineral composed mainly of calcium titanate. Perovskite has a particular crystalline structure that lends itself to solar conversion, which can be adapted to modify other materials for use in solar cells.
The problem is that earlier perovskite solar cell research was focused on lead, which is toxic, which explains why the latest news just came out yesterday from Northwestern University under the header “Taking the lead out of a promising solar cell.”
If Northwestern’s research translates into the commercial market the impact will be significant.
The new cell gets a commercial market threefer: using materials that are low cost, non-hazardous, and adaptable to a standard manufacturing process.
Northwestern hit upon the lead substitution partly because tin is in the same group in the periodic table.
The new solar cell is composed of five layers. The first two, a layer of conducting glass and a layer of titanium dioxide form the front contact. Not for nothing but titanium dioxide should ring some bells — before there was Django Unchained we had Titanium Dioxide, Unchained!.
The tricky part is the third layer, the tin perovskite in the form of methylammonium tin iodide. Methylammonium tin iodideoxidizes in contact with air, so that part of the process had to be done in a sealed environment (a nitrogen glove box, to be specific), along with the next step since the top of the tin was still exposed at this point.
The next layer is the one that closes the electrical circuit, and this part was also tricky because the team had to find something that would not eat away at the tin, which entailed a lot of digging around into the perovskite structure in order to understand its reactivity.
The final layer is a gold cap, forming the back contact electrode of the cell.
According to Northwestern, lead perovskite has about 15 percent solar conversion efficiency, and the research team anticipates that the new cell could surpass that, although right now it’s hovering at around 5.73 percent (we warned you — don’t laugh!).
Tin Perovskite Solar Cells From The UK
The UK tin perskovite solar cell announcement came out from Oxford University, a few days before the Northwestern announcement. The team’s figure for the best lead perskovite efficiency is 17 percent and their tin version came in around the same as Northwestern’s, at six percent. Like Northwestern, the Oxford team anticipates bettering the record for lead, reaching up to 20 percent or more.
The Oxford team focused on a similar problem, the degradation of the tin layer when exposed to air and moisture, and ended up with a similar solution: a sealed nitrogen fabrication environment.
Coal-Killing Solar Cells!
As for solar’s ability to compete in the electricity market with coal and other fossil fuels, the true cost of coal is finally being exposed including regional air quality and ash disposal issues on top of its contribution to global warming, and solar is already competitive with diesel in some global markets.
In the US, cheap shale gas has been pushing coal out of the electricity market and there are already indications that industries are beginning to prepare for the day when solar and other renewables push shale gas out of the energy market, by shifting into higher value products.
Exxon, for example, is looking to expand its gigantic Baytown, Texas refinery to include a gas-to-plastics operation, and the German chemical company BASF is exploring the possibility of making its largest single-site investment ever, by building a shale gas-to-plastics facility on the Gulf Coast.
By the way, we’re not exactly giving up our crushing on graphene, but you can expect to hear a lot more about perovskite from CleanTechnica from now on.
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