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No-Gold Perovskite Solar Cells Aim A Dagger At The Heart Of Fossil Fuels

The research activity around perovskite solar cells tells a story with quite an unhappy ending for coal, oil, and natural gas.

Fossil fuel stakeholders are already shivering in their boots over the low cost of wind and solar energy, and now here comes yet another dose of stone cold reality. In a new report, a research team in Italy suggests that perovskite solar cells are set for another steep drop in costs. Perovskite has great promise as a low-cost material for super cheap solar cells, so how much lower can perovskite solar cells go?

perovskite solar cell conversion efficiency

Perovskite solar cells have come a long way since the 1970s (via NREL).

Perovskite Solar Cells Have A Gold Problem

Perovskite solar cells haven’t hit the mass market yet, but the research has come a long way in recent years.

Perovskites are lab-grown crystalline materials that resemble the naturally occurring mineral perovskite. They have strong optical properties and they are relatively cheap and easy to produce at scale, which means they should replace pricier materials like silicon.

They should, but haven’t.

So, what’s holding things up?

One of the early problems was that synthetic perovskites don’t like moisture. That’s not a particularly big obstacle now that researchers have developed various types of hybrid perovskite solar cells that are more durable.

Other challenges still remain, though. One of them, identified by the Italian researchers Lucia Fagiolari and  Federico Bella of the Politecnico di Torino, is the continued use of expensive materials in perovskite solar cells.

In their new study, Fagiolari and Bella zero in on the cost of gold and other precious metals that are typically used in the back electrode of the solar cell (the front electrode is typically made of relatively inexpensive conductive glass).

They write that perovskite solar cells have “reached silicon performance” and “can accelerate the energy transition,” except that the cost of gold and other noble metals remains a stumbling block.

The high cost of the material is just part of the problem. Fagiolari and Bella also note that the method for depositing gold on the back electrode involves an “energy-consuming vacuum evaporation method.”

In addition, they take note of performance deterioration related to the use of gold and other precious metals.

A New Pathway For Perovskite Solar Cell Research

That’s the bad news.

The good news can be found in the new study, titled (spoiler alert!) “Carbon-based materials for stable, cheaper and large-scale processable perovskite solar cells,” which appears in the journal Energy & Environmental Science of the Royal Society of Chemistry.

In the study, Fagiolari and Bella undertake an intensive review of recent research activity. They conclude that carbon-based materials (surprise!) could replace gold for the back electrode in perovskite solar cells.

Specifically, they highlight graphite/amorphous carbon, graphene, and carbon nanotubes.

Aside from low cost and ease of fabrication, Fagiolari and Bella note that these materials are “highly hydrophobic.” In other words, they help solve perovskite’s moisture problem while sparing the expense of building extra moisture-proofing into the solar cell.

Fabiolari and Bella do take stock of several issues that carbon-based materials need to overcome. Nevertheless, they propose that back electrodes made with graphite and carbon black have a good chance to beat gold at its own game.

As for why they are so confident, that’s a good question. They followed the research activity and noted that before 2012, every article on perovskite solar cells dealt with liquid electrolytes. The carbon angle began to pop up after 2012, when solid-state technology made an appearance.

Meanwhile, Over At NREL

If the carbon angle doesn’t work out, fossil fuel stakeholders still have plenty to worry about. Over here in the US, the Department of Energy is a longtime fan of perovskites and its scientists are among those pursuing other promising pathways that help increase efficiency while lowering costs.

In one of the lab’s latest findings on perovskites, last April an NREL research team working with lead-based perovskite solar cells found that they could boost efficiency by replacing some of the lead atoms with atoms from tin.

The tin-perovskite angle has been tried before with limited success, but this time around there seems to be a breakthrough.

The solution involved creating a tandem solar cell and bringing guanidinium thiocyanate into the mix (tandem refers to a solar cell composed of more than one type of solar conversion material).

The guanidium compound — which by the way is also used to protect nucleic acid when removing DNA or RNA from cells — turned out to be a win-win. It nullified most of the ill effects of tin while also enabling electrons to maintain an excited state 5 times longer than shown in earlier trials.

That means the excited state lasted for just a little over one microsecond, which doesn’t sound like much, but it is a big deal. The new tandem solar cell achieved an impressive 23.1% conversion efficiency with two terminals and performed even better, at 25%, with four terminals.

NREL is riding hell for leather with a 2020 goal of achieving solar cells that cost just 6 cents per kilowatt hour in its pocket, and that’s just one example of the different avenues of pursuit the lab is pursuing.

CleanTechnica is reaching out to NREL for its insights into the area of carbon research, so stay tuned for more on that.

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Chart: Perovskite solar cell conversion efficiency via NREL.

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Written By

Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.


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