Researchers now understand how to increase efficiency of flexible solar cells

A team of researchers from MIT, with assistance from UC San Diego, have taken us one step closer to commercializing perovskite solar cells, a technology that is cheaper, more flexible, and easier to manufacture than crystalline solar cells used in conventional solar panels.

As reported by MIT News, the researchers found that by adding different metals to the mix, they can increase the efficiency of the solar cell. Adding just the right amounts, they found a ‘sweet spot’ where performance is enhanced, but found that adding too much can lead to degradation.

Perovskite solar cells aren’t actually made from the mineral perovskite. Instead, perovskite solar cells utilize a ‘perovskite structure’, wherein the solar cells are made up of three elements in a 1-1-3 structure.

The mineral perovskite is made up of 1 part calcium, 1 part titanium, and 3 parts oxygen (CaTiO3), and anything with this same ABX3 pattern is said to have a perovskite structure.

Perovskite solar cells use a complex mix of elements, but in that same structure. And it’s that crystal-like structure that allows perovskite solar cells to absorb light and transport electrical charge.

Degradation and efficiency are perovskite’s biggest challenges

Perovskite solar cells could be the next big thing for the solar industry, but there are a couple challenges researchers need to work out before that can happen.

In the lab perovskite cells work great. However, once in the real world, they quickly break down due to moisture, inclement weather, and extreme temperature. When perovskite solar cells are installed outdoors, most typically can only last a few months.

In comparison, manufacturers typically offer 25 year production guarantees for silicon-based solar panels. A research team from the Swiss École Polytechnique Fédérale de Lausanne designed an 11.2% efficient perovskite solar cell that lasted a full year without any efficiency loss, but that’s still just a fragment of conventional solar panel’s typical lifespan.

Researchers are also constantly working to increase perovskite solar efficiency, with great success. Efficiency is skyrocketing as research continues. Efficiency has jumped from about 14% in 2013 to 23% in 2018.

That might not seem too crazy, but a 23% efficient solar cell actually produces 164% more electricity than a 14% efficient solar cell (go ahead, do the math). On top of that, consider that the most efficient crystalline solar cells are 26% efficient – and they’ve been around for 60 years.

A research team from the same Swiss organization above found that they could increase cell efficiency by about 16% by adding alkali metals (which includes lithium, sodium, and caesium) to the perovskite mix. However, researchers didn’t quite know why adding these metals brought about an efficiency increase, until now.

MIT Researchers Find Path Forward for Perovskite Solar Cells

The MIT research group was able to peek into that perovskite/alkali metal mix with an ultra-small X-ray machine (about 1/1000 the width of a human hair) to watch what happens with those alkali metals in the perovskite.

They found that the metals help all the ingredients mix more smoothly together, so it’s easier for electricity to move through the material, leading to better efficiency. They also found that adding too much leads to the alkali metals clumping together, decreasing conductivity.

While the greater efficiency they saw in the lab is incredible, the real gain is finding a path forward for continuing research on perovskite solar cells. Report co-author Juan-Pablo Correa-Baena, now an assistant professor at Georgia Tech, said “The idea is that, based on these findings, we now know we should be looking into similar systems, in terms of adding alkali metals or other metals.”

This finding gives future researchers a new path to take towards increasing perovskite’s solar efficiency, hopefully leading to a faster commercialization.

Why are perovskite solar cells so promising?

Being so new, perovskite solar is still in the researching and testing phase, but the potential benefits over traditional silicon solar cells keep the solar industry continually engaged with the tech.

Compared to silicon solar cells, perovskite solar cells are easy and cheap to produce. With common crystalline silicon panels, the silicon needs to be extremely pure for max efficiency.

That ‘cleaning’ process needs expensive equipment, uses toxic chemicals, and needs temperatures up to 2,500 degrees F. On the other hand, perovskite doesn’t need any of these chemicals and can be processed in liquid close to room temperature, so manufacturing costs are much lower.

Secondly, perovskite cells also have a higher natural limit on their efficiency, or how much of the sunlight that falls on the solar cell that it can turn into electricity. While we’re currently seeing efficiency around 23%, perovskite’s theoretical limit is about 31% efficiency, according to Correa-Baena. That equates to about 30% more energy, so there’s quite a bit of room for further development.

Lastly, unlike silicon solar cells that are rigid and must be protected within heavy glass and aluminum frame, perovskite cells are actually flexible and can be supported with glass or flexible materials, so it’s much more adaptable to different situations and needs.

Many in the solar industry think perovskite solar cells are the next step in solar technology and, according to MIT, two companies are already building factories to commercialize the technology.

We’re still quite far from full-scale commercialization and deployment, though step-by-step we’re getting closer. Every year researchers find ways to increase both the lifespan and efficiency of perovskite, and hopefully soon they’ll be on-par with – or even outshine – the ubiquitous silicon solar panel.

Image Credit: CC license via Wikimedia

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