Exploring Solar Panel Efficiency Breakthroughs in 2022

There’s always the promise of some big breakthrough that’s going to change everything. Well, scientists have just smashed the solar panel efficiency record, and it could mean a big change for the future of renewable energy. This isn’t just more hype, but a sign of where things stand today and are heading. However, this isn’t the only big solar news from 2022. There’s been a lot of very recent advancements from perovskites to organic solar cells too, so what does this mean for you and me? Let’s see if we can come to a decision on this.

I’ve covered a lot of solar panel news over the past few years, as well as my experience with my own solar panels on my home. Solar power is practically the grandfather of the renewable energy family, and for good reason: there’s a limitless energy source shining down on us literally every day, just waiting to be harnessed. Just one hour of power from the sun is more than the entire world uses in a year!¹ It’s why I’m so fascinated by it, but the big downside is that we can’t capture all of that energy.

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Along those lines, many people leave comments that basically say, “solar panels aren’t efficient enough,” and most likely, “never will be.” That line of thinking always surprises me because the technologies we all take for granted today were the breakthroughs of a decade ago, so the breakthroughs of today are where things are heading.

In just the last few months, we’ve seen some exciting advancements in solar, some that we’ve been waiting for nearly ten years for. So if you’ve been holding off for the right benchmark–perhaps a target efficiency rate, or the right type of material to get into commercial use–your wait may be over, but let’s run through some of the more interesting updates, as well as some of the gotchas and what it means for us.

Record efficiency rates and design updates

First, we have to talk about some of the biggest news on the solar front, and that’s the fact that the US Department of Energy’s National Renewable Energy Laboratory just set a new solar cell efficiency record of 39.5%². This was accomplished under similar lighting conditions to the sun, which is a stark change from the last world record. Earlier experimental solar cells showed top efficiency rates of 47.1% in 2019, but that was only when exposed to extremely concentrated light³.

So how did they do it? Rather than adding more light (like the last record did), NREL’s record-breaking cells use inverted metamorphic multijunction (IMM) cells. These cells have three layers stacked on top of one another, each made of a different material: gallium indium phosphide on top, gallium arsenide in center, and gallium indium arsenide on the bottom. Each soak in a different range of light wavelengths, which lets the cell capture more energy from the whole light spectrum.You can also find three hundred “quantum wells” in the middle layer, which was the key to unlocking these cells’ new efficiency rate³ These wells extended the bandgap in the cell, which increased the amount of light that the cell could absorb overall⁴.

NREL isn’t the only one who’s had success squeezing out more energy by tweaking their solar cell design. A team co-led by the University of Surrey increased the amount of energy absorbed by their wafer-thin photovoltaic panels by 25%. The panels themselves are only one micrometer thick, but they’re made with a honeycomb-esque layer that allows for light absorption. In silicon cells, nearly ⅓ of the light that hits the cell usually bounces right off, but the textured design of these thin photovoltaic cells traps the light in the solar cell to increase the efficiency. This design was inspired by nature — butterfly wings and bird eyes already do this to some degree. In the lab, the team saw absorption rates of 26.3 mA/cm2, a 25% increase on the previous record of 19.72 mA/cm2 in 2017⁵.

The efficiency rate isn’t too shabby, either: these cells have an efficiency rate of 21%, with the expectation that further tweaks will nudge that number higher, possibly even higher than other commercially-available photovoltaics.

Perovskite developments

Solar panels usually go hand in hand with silicon (which is used in 95% of panels in today’s market), but there’s been a lingering beacon on the horizon of the solar world: perovskites. I’ve touched on these in previous videos.

Perovskites are a group of synthetic materials that are defined by their crystallographic structure. In general, they easily coat surfaces, which means that they can be used in cells on their own or in tandem with other technologies (like our existing crystalline silicon cells)⁶. These perovskite semiconductors can convert the energy-rich blue spectrum of sunlight into energy, so when used in tandem with silicon sub-cells, we can get efficiency rates of up to 30% (compared to 25% in single-junction perovskite cells)⁷.

Perovskites are meant to be the golden trio: cheap to produce, competitively efficient, and thin and lightweight enough to apply practically anywhere. That’s why researchers have been chomping at the bit to get them on the market, but there have been a few logistical hurdles before perovskites could attempt to give silicon cells a run for their money.

The first problem is one of perovskite’s biggest hurdles: the durability factor. Perovskite cell’s thin and light nature are a perk, but it also means that they’re fragile, which is not great for a material that is going to be pitted against rain, sun, hail, and everything in between. Samples used to break before researchers could even make it across the lab to be tested⁸! If the samples cannot be handled in the laboratory, they cannot withstand the occasional hailstorm or stresses applied by wind loading and torsion on the solar panel frame in the real world.

Thankfully, they’ve come a long way since then. An April study⁹ found that organometallic compounds could be used as an additive to help improve the cells’ lifespan, efficiency, and stability. The enhanced cells maintained 98% of the cell’s original 25% power conversion efficiency rate after 1500 hours of use, and they also passed the damp heat stability tests with flying colors.

Researchers have also been diving deeper into why perovskite works like it does, both the good and the bad. In May 2022, scientists at Cambridge University and Japan’s Okinawa Institute of Technology (OIST) used imaging techniques to observe the structure of perovskite films at the nanoscale, especially when light actually hits the film. They found one of the culprits behind perovskite’s infamous photodegradation problem: nanoscopic trap clusters¹⁰. These are defects in the material that show up as pockets from the cell processing, which ultimately make the film less efficient and structurally fragile. The main way to combat these efficiency-limiting carrier traps is to remove them during the manufacturing process through careful tuning of the structural and chemical design. Make these tweaks large-scale-friendly, and you have a recipe for making more of these films while also making them better in the performance department.

Organic solar cells

What if making new solar cells was as simple as printing a newspaper? That’s what the producers of organic power cells hope to accomplish, and as of now, they’re ready to push this tech into the worldwide market.

Organic power cells are made by printing photovoltaic material onto flexible materials like plastic sheets. These paper-thin solar cells are composed entirely of organic materials: flexible, lightweight, and quick to manufacture with printing technology (the same process as printing newspapers!)¹¹ They cost half as much to make as silicon-based cells, and they’re also 100X lighter. Each square meter weighs less than 2 kilograms, and that’s likely to dip down to 1 kilogram in 2023¹².

Unlike silicon cells, their conversion efficiency rate doesn’t drop when used indoors, which makes them extra appealing for devices like smart speakers, sensors, and other wearables that may not get to see a lot of actual direct sunlight. This makes use of existing ambient light, converting some of it to electrical power reducing the load on small batteries and charging devices.

The efficiency rate leaves a little to be desired at 10%, but these cells can also be used for around 20 years¹², which already dwarfs the current perovskite lifespans (more on that later). As more businesses start to ramp up production, that mass production has the potential to cut the costs in half.

These “print-to-order” solar cells are starting to hit the market on a global scale. German startup Heliatek is beginning mass production of organic solar cells as early as this year, with a goal to produce 600,000 square meters (and a max production capacity of 1.1 million square meters a year!) Brazilian startup Sunew also has these organic cells in production, producing over 10,000 square meters of organic solar cells so far for vehicle rooftops (since they’re big electric-vehicle fans). Sweden’s Epishine put its miniature solar harvesting modules on the market just this past December, boasting an energy-conversion rate of 13% and a lifespan of 10 years. These can be used for temperature and humidity control sensors, fire alarms, card readers, and other small–yet important–devices that often blend into the background. And then you have Ricoh in Japan, starting on a smaller scale. They only produce 100 square meters a year, but that’s enough to power 50,000 small smart devices, from wearables to safety sensors in tunnels and bridges¹⁶.

Even these cool cells have room to improve, and researchers have found two key developments with the potential to really help organic cells capture that spark.

Strap yourself in, we’re going to get real nerdy in here. Let’s talk chirality.

DNA (and other helix-shaped molecules) are considered chiral. That design is everywhere in nature, and it’s key to practically everything from our genetic makeup to photosynthesis. They’re asymmetrical, and as electrons go through the structure, they separate charges created by the light (meaning that light can be converted into biochemicals more efficiently).

Now usually, molecules stay with their own structural cliques … it’s kind of like high school … (chiral with chiral, achiral with achiral, etc). However, researchers at the University of Illinois Urbana-Champaign found that when they applied achiral conjugated polymers with a solvent, the solution eventually evaporated to leave behind reassembled polymers: more specifically, helixes, aka, chiral structures¹¹.

Going from achiral to chiral structures is a pretty big deal, especially when it comes to applying the idea towards organic solar energy. In theory, scientists can apply that chiral structure (and all the energy-producing goodness that comes with it) to materials that normally require achiral conjugated polymers to function, like solar cells.

Secondly, let’s talk about everyone’s favorite subject: perfluorinated sulfuric acid ionomers. (No? Just me?) Let me explain: to make fully-printable organic solar cells, you need hole-transporting materials. That’s hole, not whole … you gotta love the english language. These are HTMs for short. One such promising HTM has been poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a conducting polymer complex that is used to make printable devices¹³. It’s been around since the 1990s, but it’s falling short today. Unfortunately it disperses in water and is very acidic, which can impact the efficiency and stability of the PEDOT:SS-based solar cells.

To combat this, researchers at the Huazhong University of Science and Technology and the Institute of Materials for Electronics and Energy Technology (i-MEET) have come up with PEDOT:F, a new polymer complex that disperses in alcohol and has low acidity. With this new formula, organic photovoltaics have been shown to have a power conversion efficiency of 15% and retained 83% of their initial efficiency under constant illumination at maximum power for a total of 1,330 hours¹³.

These new solar developments may not be the most attention-grabbing to the average person, but they are a clear sign that there’s still more to solar energy on the horizon. So what can we actually take from these developments, and what does it mean for the industry at large?

Record-breaking efficiency and design

First, as exciting as breaking the world record of solar efficiency is, NREL’s solar cell design still has its own disadvantages. For one, producing this type of cell is still going to be expensive at this point, which is a problem that already hobbles the renewable energy industry at large. Mass producing cells with this level of efficiency may still be a long way off, and we would need to find a way to do so while keeping the overall costs low enough to not price major consumers out of the market.

The University of Surrey’s honeycomb design, on the other hand, seems to target that problem directly. These cells use less silicon overall, which translates to cost savings in the production process. There’s a lot of potential to how we can use them, too: even while textured, the film layer is still super thin, which makes them light and versatile enough to go practically anywhere!

The next step is to get the show on the road by finding commercial partners and developing manufacturing techniques. As you may have guessed, that’s no small feat in itself, and for now, this design is still a long way from the market, an unfortunate fate for many promising renewable technologies in the making.

Perovskites

So how about perovskites, the solar industry’s shining beacon and simultaneous problem child?

Perovskite cells are finally on the market now, but they’re nowhere near where fans hoped they would be, and they’re definitely not over the commercialization hurdle just yet. A lot of this can be attributed to their fickle nature in the field. Both silicon and perovskite solar cells have set records above 25% recently, so the power itself isn’t necessarily the problem: it’s the endurance.

Unfortunately, perovskite cells in the field lose 10% of their cell’s efficiency after a few months of use. When you compare that to silicon cells–whose manufacturers guarantee that panels will maintain 80% of their performance for sometimes 30-40 years–that’s a tough act to follow. Perovskite cells need to last at least 20 years in the field to meet the US Department of Energy’s Solar Energy Technology Office (SETO) 2030 goals of $0.02/kWh¹⁴.

Manufacturing will likely be the final major hurdle to commercializing perovskite solar panels. It’s a bit of a catch 22: we need financing to scale up manufacturing and develop cells at large scale, however, financing will only be available when the scale up looks feasible.

Here’s the good news: perovskites don’t HAVE to outshine silicon cells. You can also use them in tandem cells, where a perovskite layer is stacked on TOP of a silicon cell . (Talk about the best of both worlds!) The materials absorb different light wavelengths, which means you get complementary energy harvesting.

Organic cells

So how about organic cells? The idea itself is still pretty attractive. These types of cells could use their lightweight and flexible nature pretty much anywhere, from domed roofs, glass, and other oddly-shaped surfaces that couldn’t support the heavier silicon-based panels.

These guys probably won’t be powering your neighborhood anytime soon, but they have found their own special niche: specifically, smaller devices, including wearables.

Why are wearables such a big deal? Most use single-use batteries that need to be replaced every 1-2 years. That’s a big deal for this segment when the global market for smart sensors alone is expected to reach $29.6 billion in 2026, according to MarketsandMarkets. Current solar tech doesn’t quite cut it for these smaller applications yet, as silicon doesn’t work as well indoors, and perovskite cells only last a few years at a time.

True, their efficiency rate is still a little skimpy (at least, compared to their other solar counterparts). Hopefully, further studies into chirality and other polymer solutions may help boost that efficiency rate in the long run, making the “printable solar cell” a staple in the solar community.

While we’re most likely still a few years away from seeing these admittedly cool developments actually make ripples on the market, it’s a clear sign of where things are heading. However, if you’re considering solar for your home, don’t wait. Solar panels are efficient enough today to achieve a lot of the goals you probably have for your home. Waiting for the next big thing pretty much ensures that you’ll always be waiting … because there’s always something better around the corner. If you live in the US, don’t miss out on the current Federal tax solar rebate, which will be dropping at the end of the year. You can use my EnergySage portal to help research and get quotes from installers in your area. I used EnergySage to research products and find my own installer for my house and absolutely loved the experience. Don’t wait and miss out.