Perovskite semiconductors for solar photovoltaic cells

[Astronuc]

I heard this while driving the other day.

Progress On Perovskite Solar Cells | Earth Wise with Randy Simon​

https://earthwiseradio.org/podcast/progress-on-perovskite-solar-cells/

Perovskites are semiconductors with a specific crystal structure. Their properties make them well suited for making solar cells. They can be manufactured at room temperature, using much less energy than it takes to make the silicon-based solar cells widely used today. As a result, perovskite solar panels would be cheaper and more sustainable to produce. Manufacturing silicon solar cells takes a lot of energy because silicon is forged at around 3000 degrees Fahrenheit. In addition, perovskites can be made flexible and transparent, making it possible to use them in ways unavailable with silicon solar technology.​

But unlike silicon, perovskites are very fragile. The early solar cells made from perovskites in 2009 and 2012 lasted for only minutes. Lots of potential, but little practicality.

Recently, Princeton Engineering researchers have developed the first perovskite solar cell with a commercially viable lifetime, which is a major breakthrough.

I wanted to check this out. Si melts at about 2,570°F (1,410°C). I'm not sure about 3000°F (1649°C), which incidentally is a temperature at which we have tested stainless steel in order to understand its mechanical behavior under a hypothetical accident. Above melting, one does not forge - one pours, or grows a crystal from a liquid pool. But I digress.

Of more interest - Princeton Engineering researchers have developed the first perovskite solar cell with a commercially viable lifetime, marking a major milestone for an emerging class of renewable energy technology. The team projects their device can perform above industry standards for around 30 years, far more than the 20 years used as a threshold for viability for solar cells.
https://engineering.princeton.edu/news/2022/06/13/loo-30-year-perovskite-solar-cell

Paper - Accelerated aging of all-inorganic, interface-stabilized perovskite solar cells
https://www.science.org/doi/10.1126/science.abn5679

 

[berkeman]

A couple questions...

** Where does the name Perovskite come from?

** I only skimmed the popular article, but what was the breakthrough that made the fabricated solar cells so much more robust compared to the initial ones that were so fragile?

Thanks.

 

[Astronuc]

** Where does the name Perovskite come from?

"Perovskite is a naturally occurring mineral of calcium titanate with a chemical formula of CaTiO₃. This mineral was first discovered by German mineralogist Gustav Rose in 1839 and was named in honor of the Russian mineralogist Lev Perovski (1792–1856)."
Ref: Suneth C. Watthage, Zhaoning Song, Adam B.Phillips, Michael J.Heben, "Evolution of Perovskite Solar Cells," in Perovskite Photovoltaics: Basic to Advanced Concepts and Implementation, Sabu Thomas
and Aparna Thankappan, Eds., Elsevier/Academic Press, 2018
https://www.sciencedirect.com/science/article/pii/B9780128129159000034
https://www.sciencedirect.com/book/9780128129159/perovskite-photovoltaics#book-description

Another author, P.C. Reshmi Varma, in the same text indicates, "The discovery of calcium titanate (CaTiO₃) in 1839 by a Russian mineralogist Perovski was considered to be the origin of perovskite, and materials with the same type of crystal structure as that of CaTiO₃ were known as the perovskite materials (structure)."
https://www.sciencedirect.com/science/article/pii/B9780128129159000071

Some introductory summaries on perovskites can be found here -
https://www.sciencedirect.com/topics/earth-and-planetary-sciences/perovskites

what was the breakthrough that made the fabricated solar cells so much more robust compared to the initial ones that were so fragile?

According to the Earthwise summary, "The research team has developed an ultra-thin capping layer between two of the layers of a perovskite solar cell. The layer is just few atoms thick but has been demonstrated to dramatically increase the durability of the device."

From the engineering.princeton.edu article:

Xiaoming Zhao, a postdoctoral researcher in Loo’s lab in the Andlinger Center for Energy and the Environment, had been working on a number of designs with colleagues. The efforts layered different materials in order to optimize light absorption while protecting the most fragile areas from exposure. They developed an ultra-thin capping layer between two crucial components: the absorbing perovskite layer and a charge-carrying layer made from cupric salt and other substances. The goal was to keep the perovskite semiconductor from burning out in a matter of weeks or months, the norm at that time.

It’s hard to comprehend how thin this capping layer is. Scientists use the term 2D to describe it, meaning two dimensions, as in something that has no thickness at all. In reality, it’s merely a few atoms thick — more than a million times smaller than the smallest thing a human eye can see. While the idea of a 2D capping layer isn’t new, it is still considered a promising, emerging technique. Scientists at NREL have shown that 2D layers can greatly improve long-haul performance, but no one had developed a device that pushed perovskites anywhere close to the commercial threshold of a 20-year lifetime.

Zhao and his colleagues went through scores of permutations of these designs, shifting minute details in the geometry, varying the number of layers, and trying out dozens of material combinations. Each design went into the light box, where they could irradiate the sensitive devices in relentless bright light and measure their drop in performance over time.

In the Science article, one finds the statement "Zhao et al. found that for all-inorganic cesium lead triiodide (CsPbI₃) solar cells (perovskite), a two-dimensional Cs₂PbI₂Cl₂ capping layer stabilized the interface between the CsPbI₃ absorber and the copper thiocyanate hole-transporter layer and boosted its power conversion efficiency to 17.4%."

 

[Tom.G]

That Science article (which I happened to read about the same time @Astronuc did) also pointed out that the life tests were indeed lab tests and that the 'real world' usage environment has many other degrading factors in its toolbox.

" It is worth highlighting that real-world operating conditions vary by geographic location and mounting conditions. For example, a module may occassionally experience 85°C in Saudi Arabia, with a time-averaged temperature of up to 55°C, whereas the climate conditions will be much more benign in temperate regions such as Germany, where there are fewer extreme temperature spikes and an average temperature well below 35°C."

The encapsualtion approach is definitely good news, just how good will take some weeks to determine.

"...onward and upward till the goal ye win."
(Frances Anne Kembel, addressing the Young Gentlemen leaving the Lenox Academy, Massachusetts, about 150yrs ago)

 

[Astronuc]

I'm used to thinking of perovskites as M₁M₂O₃, e.g., (CaTiO₃), as opposed to the more general M₁M₂X₃, where M₁ is a metal, usually group 2 (alkaline earth), M₂ is a transition metal, and X would be anything from group IVA (14) to group VIIA (18). I'm more familiar with X = O.

https://www.sciencedirect.com/science/article/pii/B9780081029084001855
From John F.W. Bowles, Oxides, in Encyclopedia of Geology (Second Edition), 2021

Perovskite (CaTiO₃) has an orthorhombic structure (space group Pbnm). A large number of compounds with the general formula ABO₃ have the perovskite structure; in many of these, as in perovskite, A is divalent and B is tetravalent so that Ca can be partially or totally replaced by Na, Mn, Ce, Sr, Pb and Ti by Fe, Nb, Zr and Mg with the valency accommodated by paired substitution such as Fe³⁺ + Nb⁵⁺ replacing Ti³⁺.