New Triple-Junction Tandem Perovskite Solar Cell Sets World Record – CleanTechnica

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Research activity in the perovskite solar cell field began to stir in the early 2000’s, with US scientists and innovators in the lead. Now all that hard work is about to pay off — in other nations, that is. The US isn’t entirely sidelined, but this year’s sharp U-turn in federal energy policy has sucked some air out of the room, giving other countries an opportunity to shine. The latest example comes from Australia, where a research team based at the University of Sydney has reported a new milestone for perovskite solar conversion efficiency and stability.

The Perovskite Solar Cell Difference

Perovskites are finicky crystalline materials based on the structure of the naturally occurring mineral perovskite. Applications to the field of photovoltaics lay dormant for about 160 years after perovskite was first unearthed in the Ural Mountains back in 1839. A team of researchers in Japan finally published the first known perovskite solar cell in 2009 and it was off to the races, with the US among those attracted by a low-cost material with superior optical properties (see more perovskite background here).

There being no such thing as a free lunch, ever since 2009, researchers have been hammering away at the downside of perovskites, which is their lack of durability. In recent years, the research field has coalesced around the idea of fabricating tandem solar cells consisting of perovskites and silicon, the more familiar foundation of conventional solar cells.

Silicon is durable but expensive, while perovskite is inexpensive and efficient at converting sunlight to electricity. Combine the two and you get a more efficient, less expensive solar cell than silicon alone, plus the durability.

Research Team Concocts A Tandem-Tandem Perovskite Solar Cell

Nobody ever said that a tandem perovskite solar cell has to use only one layer of perovskite, and that’s where the University of Sydney comes in.

Solving the durability issue with silicon is just half the battle. The other half is scaling up the new solar cell into a commercially deployable product. To address the scale issue, the researchers created a triple-junction solar cell architecture consisting of two layers of perovskite plus silicon.

The result, published in the journal Nature Nanotechnology, is a solar cell measuring 16 square centimeters (about 2.5 square inches). The new cell achieved a conversion efficiency of 23.3%, which according to the researchers is the highest reported so far for a device of this size.

The team also reported a record 27.06% conversion efficiency for its much smaller, 1 square centimeter “champion” cell.

Small Tandem Perovskite Solar Cell, Big Significance

Neither the larger nor the smaller version are anywhere near the size of a commercially available solar cell. These typically weigh in at 6×6 inches or thereabouts. Still, the Sydney results could have an outsized impact on developments in the solar marketplace if further scale-up is achievable.

As pointed out by the research team, the smaller cell set a new standard for thermal stability, meaning the ability of the device to withstand heat.

“In a global first, the 1 cm2 cell passed the International Electrotechnical Commission’s (IEC) Thermal Cycling test, which exposes devices to 200 cycles of extreme temperature swings between -40 and 85 degrees,” the researchers explained.

“This cell retained 95 percent of its efficiency after more than 400 hours of continuous operation under light,” they added.

The larger cell demonstrated the potential for linking thermal stability with high efficiency. “We improved both the performance and the resilience of these solar cells,” summarized research team leader Professor Anita Ho-Baillie, who holds the title of John Hooke Chair of Nanoscience at the University of Sydney Nano Institute and School of Physics.

“This not only demonstrates that large, stable perovskite devices are possible but also shows the enormous potential for further efficiency gains,” Professor Ho-Baillie noted.

“This is the largest triple-junction perovskite device yet demonstrated and it has been rigorously tested and certified by independent laboratories,” she emphasized. “That gives us further confidence that the technology can be scaled for practical use.”

How Did They Do It?

For those of you with time on your hands, the full study is available under the title “Tailoring nanoscale interfaces for perovskite–perovskite–silicon triple-junction solar cells.”

“Triple‐junction solar cells theoretically outperform their double-junction and single‐junction counterparts in power conversion efficiency, yet practical perovskite–perovskite–silicon devices have fallen short of both theoretical limits and commercial targets,” the researchers explain, by way of explaining the challenge.

The solution involved removing methylammonium (an acidic formulation of the industrial and pharmaceutical chemical methylamine), and replacing it with the element rubidium. Methylammonium is commonly used to improve the efficiency of perovskite solar cells, but it produces a perovskite lattice prone to defects and degradation.

The researchers also replaced lithium fluoride, another common but less stable perovskite surface treatment, with the chemical piperazinium dichloride, which also has pharmaceutical applications.

Solar Gold For A Gold Bug

The research team also developed a new architecture to connect the two perovskite junctions while maintaining conversion efficiency and durability. Their solution is one that could warm the heart of notable solar foe and US President Donald Trump because it deploys his favorite material, that being gold.

The team determined that the filmlike appearance of gold at the nanoscale is not a continuous film at all, but an arrangement of nanoparticles. With this new knowledge in hand, they engineered a gold junction connection with optimal electric charge and light absorption properties.

“It is an exciting time for solar research,” Ho-Baillie enthused in a press statement. “Perovskites are already showing us that we can push efficiencies beyond the limits of silicon alone. These advances mean we are moving closer to cheaper, more sustainable solar energy that will help power a low-carbon future.”

For the record, the new perovskite solar cell research was a collaborative effort that engaged partners from China, Germany, and Slovenia.

Meanwhile, Over In The USA

It may be somewhat of a surprise to see Slovenia emerging in the vanguard of advanced perovskite solar cell research. Slovenia is sometimes referred to as a former Eastern bloc state. However, the connection is a distant one. Slovenia broke away from Yugoslavia in 1991, more than 40 years after Yugoslavia separated itself from the USSR.

Besides all that, Slovenia is not the only nation in the eastern regions of Europe to dip its hand in the perovskite solar cell field. In another recent development, a research team at Kaunas University of Technology also drew upon international expertise to report a highly efficient, highly stable inorganic perovskite solar cell.

The researchers focused on a new passivation formula, with passivation referring to a surface layer that renders the cell chemically inactive, protecting it from degradation.

Interested? Check out their study under the title “Cation interdiffusion control for 2D/3D heterostructure formation and stabilization in inorganic perovskite solar modules” in the journal Nature Energy.

Photo (cropped): An international research team based at the University of Sydney in Australia has created a highly efficient, durable tandem perovskite solar cell, deploying two perovskite layers along with a silicon layer (courtesy of University of Sydney).