How Low Can Solar Cells Go? Perovskite Researchers Say Down, Down, Down

February 21st, 2020 by Tina Casey

The cost of solar power is sinking practically by the day, and the next new “hot” solar cell material — perovskite — will push costs down even more. So far you can’t get perovskite solar cells in stores but this year will bring a trickle into the market, and a batch of new research suggests that the trickle will become a flood. When that happens, look out. The thermal coal market is already in the toaster and perovskite could fry it to a crisp while also dragging natural gas down along, too.

Perovskite For More & Cheaper Solar Cells

Perovskite is a naturally occurring mineral (aka calcium titanate) that has been known to science since its discovery in the Ural mountains in 1839.

Science may have known perovskite, but researchers didn’t fully cotton on to its photovoltaic properties until the 1950s.

Synthetic perovskite is relatively inexpensive and easy to make, which brings up the prospect of using it as a substitute for silicon, the main ingredient in today’s solar cells. Silicon is efficient but pricey, and the hunt has been on for substitutes.

That brings us up to today, when researchers have figured out how to resolve the Achilles’ heel of perovskite, which is its tendency to fall apart in humid conditions. One solution, for example, is to add a dose of graphene to the mix.

NREL To The Rescue With Sealed-In Perovskite Solar Cells

Another piece of the puzzle is the use of lead in perovskite solar cells. According to our friends over at the National Renewable Energy Laboratory, adding lead in minute quantities can ramp the efficiency of perovskite solar cells close to the 25% range. Without that assist, efficiency is cut in half.

The problem is that lead is toxic in the environment, and the form of lead used in perovskite cells dissolves in water. That’s actually not a problem if the cell is just sitting there undisturbed, but lead could be exposed if the cell is damaged.

A team of researchers from NREL has figured out a way to practically eliminate that risk. Their solution is to coat both sides of the cell with a durable lead-absorbing film.

How durable? Check into the journal Nature and get all the details from their paper, “On-Device Lead Sequestration for Perovskite Solar Cells,” which describes tests that involved hammers, knives, and acid, among other stressors.

A Market-Ready Perovskite Cell From Panasonic

Meanwhile, Panasonic and NEDO (Japan’s New Energy and Industrial Technology Development Organization) have been working on bringing manufacturing costs down for perovskite solar cell modules.

In the latest development, the collaboration has resulted in a 16.09% efficient PV cell that can be fabricated by deploying a high volume, high throughput process similar to inkjet printing.

Aside from bringing down costs, the lightweight cell can operate efficiently in applications where silicon solar cells are impractical, such as windows and building facades.

A conversion efficiency of 16.09% is pretty decent for that type of cell, but the partners plan on tweaking their perovskite formula for future improvements. In any case, the lower efficiency is balanced out by the potential for covering larger areas at less expense.

Perovskite & Silicon Together

On the higher end of the efficiency scale is the strategy of combining perovskite with silicon in a single tandem solar cell. The latest development on that score comes from a research team at the Kaunas University of Technology, in Lithuania.

Their new perovskite-silicon tandem cell has been Fraunhofer-certified at 29.15% efficiency, a record-breaker for that type of cell.

The basic idea is to use low-cost perovskite a a means of stretching out the more expensive silicon.

According to the researchers, one gram of silicon is only good for producing a few square centimeters of solar material. Their tandem material can cover up to 1,000 square meters.

On the manufacturing side, costs are lowered by deploying a self-assembly process. Here’s the explainer from the school:

“The self-assembled monolayers (SAMs) are as thin as 1-2 nm, covering all the surface; the molecules are deposited on the surface by dipping it into a diluted solution. The molecules are based on carbazole head groups with phosphonic acid anchoring groups and can form SAMs on various oxides.”

Got all that? A company called Tokyo Chemical Industry Co. certainly did. The Japanese company has already purchased a license to produce the tandem material.

Meanwhile, other researchers have been tackling the lead issue by exploring tin as an alternative material.

As for when those new perovskite PV cells will hit the shelves of your local hardware store, CleanTechnica has reached out to the UK company Oxford PV for an update on its timeline for 2020, so stay tuned for more on that.

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Photo: Perovskite solar cell via Panasonic.









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