2024 Perovskite Breakthroughs are the Future of Solar

Perovskites are often hailed as the next big thing for solar panels. They’re more efficient than silicon PVs could ever be, and they have higher yields. However, their fragility and short lifespans have relegated them to the lab…so far.

But 2024 is looking to be the year of the perovskite. The last few months have seen new perovskite researchers all over the world smashing records, including durability. Because of this, some of these new perovskites are even set to hit the market this year. Let’s check out some of the most exciting breakthroughs in the field and see for ourselves if perovskites are finally ready for their big debut. And why should you care?

Perovskite Recap

It truly feels like we’re at the beginning of a massive paradigm shift for solar. Researchers are breaking so many different perovskite records using such widely varied techniques within the last few months, it’s mind blowing. Some teams are coming at this from a chemistry angle, trying to engineer tougher perovskites. Others are looking at the very architecture of a perovskite PV, experimenting with under-studied cell blueprints and achieving surprising results. Then there’s those who are having those random “eureka” moments that make for great science stories, when making one little change causes everything to fall into place. There’s just so many wild advances all happening at once. With so many discoveries, it stands to reason that there’s hope for at least some of them to reach the market.

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Let’s back up first, though. What are perovskites? We’ve talked about them before on the channel, so here’s a quick TL;DR. They’re a family of crystalline materials with the same crystal structure as calcium titanate. Current silicon solar cells only capture around 20% of usable sunlight, meaning we’re leaving about 80% on the table. Perovskites have the potential to use more of that sunlight, and may easily break that 20% figure; they might be able to break silicon’s theoretical maximum efficiency of 29%.¹

Better yet, they can be “tuned” to capture light from parts of the spectrum that silicon PVs can’t touch. This is good on its own merits, and it also allows you to Voltron perovskite and silicon layers together to form “tandem” cells that capture much more light than either could on their own while sharing the same footprint.² To sweeten the deal even further, perovskites are also relatively easy to synthesize and produce.

To give you an idea of just how big of a deal increasing solar panel efficiency is, we can take a look at my own home as a point of comparison. I have REC 400 Watt panels on my house, which have a rated efficiency of about 21.6%. With four hours of sun a day, a single REC 400 panel would generate about 576 kWh/year. These are high level calculations and don’t take local conditions, inverter hardware, etc. into account. Upping that efficiency (with the same exact single panel footprint) to something like 25% may not sound like a big jump, but would produce about 682 kWh/year. That’s a 15% jump in output overall. That would mean instead of needing something like 30 REC panels to achieve my energy goals at 21.6% efficiency, I’d only need 25 panels at 25% efficiency.

So what’s the catch? Cost is usually the issue with these sorts of things, but not here. Believe it or not, perovskites aren’t prohibitively expensive. In fact, easy manufacturing techniques and widely available materials mean perovskites can be cheaper than silicon PVs.³⁴ That means that in my hypothetical example, I would not only need fewer panels to achieve my goals — they’d theoretically be cheaper per panel, too. No, the real issue is their durability.

While they’ve performed very well in lab conditions, perovskite cells degrade very quickly out in the real world. Some can see a capacity dip as large as 80% in two years or less.⁵ Compare that to my REC 400 panels with a 25 year warranty that guarantees only about an 8% dip by the end of the warranty. What’s killing perovskite cells so fast? Heat, moisture, oxygen, and even UV rays…y’know, all the things that a solar panel is going to have to face day in and day out.

We can’t slather our solar panels in a nice coat of sunscreen, so the benefits we mentioned a minute ago are effectively locked behind the durability problem. And that’s why finding a solution to it has become something like the holy grail of solar tech. That brings us to the big question: has anyone made any progress solving this problem, or are perovskites a dead end? And if they are, what other pathways are there to solar advancement?

New Developments

Well, good news. The UK-based company Oxford PV returns to this channel yet again. And this time, they’ve solved the perovskite durability issue! So what do you think? Jump in the comments and let me… no, no I’m kidding, don’t click off!

Now, it is true that Chris Case, Oxford PV’s Chief Technology Officer, told the Wall Street Journal that the company’s cells are designed to meet or beat a 25-year life span. Oxford PV says it’s proved this by studying full-size modules in outdoor environments for over three years, then used that data to predict long-term stability.⁶ These studies also show that its best tandem cells lose only about 1% efficiency in their first year of operation and have a very small rate of decline thereafter.¹ Frustratingly, these results have yet to be published, though this could be for proprietary reasons.⁶ After all, if you’re the only one who cracked the tough perovskite code, well, there’s going to be a lot of value in that.

That said, Oxford PV is making definite progress. It’s teamed up with the Fraunhofer Institute for Solar Energy Systems (FISES) in Germany, which recently used Oxford PV’s tandem cells to construct a working solar module. FISES just announced that this module achieved a record breaking 25% conversion efficiency.⁷⁸ Remember what that could mean based on my calculations earlier: about a 15% increase in power output over a year. Now that the efficiency is confirmed, FISES and Oxford PV are working towards certifying that all-important longevity stat. To this end, they’re putting the module through a battery of intensive long-term stability tests.⁸ And while it pays to be skeptical about these sort of breakthroughs, I should note that Oxford PV’s factory in Brandenburg, Germany, is set to begin commercial production of their tandem solar cells later this year.⁸ So, if all goes according to plan, we won’t have to wait long to put them to the test.

In other developments, an international group of scientists led by the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia are taking a different approach to perovskites. Rather than focusing on making better materials, they’re optimizing how we assemble those materials for maximum energy generation and efficiency.⁹

You see, one of the main limiters of solar cell efficiency is the mobility of its charge carriers. Charge carriers are the electrons and “holes” knocked free from their homes inside the cell by incoming solar energy. The movement of electrons is, by definition, electrical current. “Holes” are places where an electron could go, so their “movement” is really the movement of electrons as well. It’s actually these charge carriers that we use to create the flow of electricity, not the sunlight itself. That’s an oversimplification in the interest of time, so if you want to know more check out some of my other solar panel videos.

Anyway, part of what makes perovskites so efficient is that they allow those charge carriers more mobility than they get in a silicon cell. Even still, the majority of these carriers are usually “captured” by the material they’re conducting through, or defects within the cell, long before they can reach the electrodes to be used as electricity.¹⁰ Not great.

This has led some engineers to add an extra layer to the cells to help facilitate the capture of those charge carriers. Solar cells have a P-layer (home of holes) or the N-layer (home of electrons). The light capturing “I-layer” of perovskite sits between the two layers. This gives us two possible types of architecture depending on which layer you want the sunlight to touch first: the hole-layer (P-I-N) or the electron-layer (N-I-P).¹¹¹²

Each architectural style has its strengths and weaknesses, and explaining them all could be its own video. To keep it brief, the electron-first N-I-P style is physically easier to construct, which means it’s more common and better-studied. It also helps that most of the efficiency records are currently held by team N-I-P.¹¹ But recent research suggests that P-I-N variants are much more durable than their counterparts, and some can even match the N-I-P’s efficiency.

This is where the Saudi researchers are making progress. They’ve developed a novel P-I-N setup with enhanced ligands, that’s the stuff that bonds the perovskite to the other layers. It also acts as a kind of capstone or varnish on top of the perovskite layer to protect them.¹³ The result is a perovskite P-I-N cell with a very good power conversion efficiency of 25.63%. After 1,000 hours of testing in 85 C (about 185 F) temperatures, they only degraded by 5%.⁹¹⁴

In yet another recent efficiency and durability breakthrough, a team led by scientists from the Korea Institute of Energy Research (KIER) have broken records for semi-transparent perovskite PVs.¹⁵ They focused on semi-transparent perovskite cells, because they show a lot of promise when used in windows and bifacial PVs. Why?

A solar cell requires electrodes. For mechanical reasons, these electrode layers are best positioned as the outer part of the cells. It’s like the bread of our solar sandwich. Of course, electrodes aren’t perfectly invisible, so they tend to block some of the light. As a result, they tend to only end up on one side of the cell. But what if we could make transparent electrodes? Well…we can. They’ve already been around for years.¹⁶ So why aren’t all PVs equipped with transparent electrodes? Why aren’t all our windows doubling as perovskite cells right now?

Here’s the thing: transparent electrodes cause PV cells to degrade much faster because they don’t screen out high-energy particles that damage the hole-transportation-slash-N-layer — all that stuff we talked about earlier. KIER scientists fixed it by adding a metal oxide layer to screen out those particles and they found… even more efficiency and fewer degradation issues?!¹⁷¹⁸

The Energy AI and Computational Science wing of the KIER team took a look at the data and discovered that the N-layer was reacting unexpectedly with the metal oxide. Normally, lithium is added to an N-layer to make it more conductive and improve efficiency. Turns out the lithium ions were diffusing into that metal oxide blocker and making them both less effective.

However, the KIER scientists found a pretty elegant solution. Lithium ions already oxidize into lithium oxide. Previously, the lithium oxide was assumed to be a harmless byproduct of this process. The KIER team deliberately converted the flighty lithium ions into stable lithium oxide, and voila, enhanced durability and efficiency. Their semi-transparent solar cells hit an efficiency of 21.68%, making them the most efficient among the transparent perovskites electrodes in the world. Better yet, they retained 99% of their initial efficiency after 240 hours of operation, and their stability rating remained at 99% for 400 hours.¹⁵¹⁷ If you’re curious about transparent solar cells, I’ve got a video that does a deeper dive on them that I’ll link to in the description.

But it’s not all good news. We need to talk…about CubicPV. The company is backed by Bill Gates, and given his greentech investing record, it’s up to you if that’s a good thing or not. Just days after my 2023 solar panel update video was released, CubicPV announced that, thanks to incentives in the Inflation Reduction Act (IRA), it was going to build a 10 GW conventional mono wafer factory.¹⁸ This was set to fill a supply chain gap here in North America and create an estimated 1,500 green energy jobs.¹⁹

Awesome. So what’s the bad news? Well, CubicPV recently announced that it’s shifting to tandem perovskite cells instead, abandoning the wafer factory in the process. Think about that: A major company ran the numbers and was so confident that perovskite tandem cells were the future that it abandoned its silicon wafer plans mid-stream. Surely a promising sign for the future of perovskites, right? But definitely not great for the community that was looking forward to the previous promise of a bunch of good, green jobs.²⁰²¹

Another thing about CubicPV: it’s claiming to have tackled perovskites durability issues through “better chemistry” and by “building intrinsic stability into the material itself.”²² There’s no further data on how the company is planning on doing this, which doesn’t make me very confident. Given that they’re working on a proprietary method to manufacture a lot of perovskite cells in a fast, cheap, and energy efficient manner, it is possible that CubicPV’s perovskite chemistry is proprietary too. Great if it ever comes to fruition, but again, I remain skeptical until I see some hard evidence.

So, perovskites remain the solar MacGuffin, but it does feel like we’re making real progress here. If just one of these companies has truly solved the durability issue, we could be on the cusp of a solar revolution. The market certainly seems to think we’re on our way. The global perovskite solar cell market size was just $94.8 million in 2022. It’s expected to balloon to around $2.479 billion by 2032.²³ Even if these predictions are wrong and they’re not the next technological leap in the solar sphere, their efficiency ratings are so impressive, they’ll probably find their niche no matter what.