There's always the hope of a huge breakthrough that will change everything. Scientists have just broken the solar panel efficiency record, which might have far-reaching implications for the future of renewable energy. This isn't just more hype; it's a reflection of where things are now and where they're going. However, this isn't the only significant solar news to come out of 2022. There have been several recent advances in everything from perovskites to organic solar cells, so what does this mean for you and me? Let's see if we can get an agreement on this.
Over the last few years, I've covered a lot of solar panel news, as well as my own experience using solar panels on my home. Solar power is the patriarch of the renewable energy family, and for good reason: there is an infinite energy source shining down on us every day, just ready to be harnessed. One hour of solar energy is enough to power the entire earth for an entire year! 1 That is why I am so attracted by it, but the major disadvantage is that we cannot harness all of that energy.
Along those lines, many people make comments saying that "solar panels aren't efficient enough," and that they "probably never will be." That line of thought always amazes me because the technology we all take for granted today were breakthroughs a decade ago, ergo the breakthroughs of today are where things are headed.
We've seen several great solar breakthroughs in the last few months, some of which we've been waiting for nearly ten years. So, if you've been waiting for the perfect benchmark—perhaps a target efficiency rate or the right type of material to enter commercial use—your wait may be over, but first, let's go over some of the more fascinating improvements, as well as some of the gotchas and what it all means for us.
Keep track of efficiency rates and design changes.
First, we must discuss some of the most recent solar news, which is that the US Department of Energy's National Renewable Energy Laboratory just established a new solar cell efficiency record of 39.5%2. This was performed at identical lighting circumstances to the sun, which is a significant improvement over the previous world record. Earlier experimental solar cells attained 47.1% efficiency rates in 2019, but only when subjected to extremely concentrated light3.
So, how did they pull it off? NREL's record-breaking cells use inverted metamorphic multijunction (IMM) cells rather than adding extra light (as the previous record did). These cells are made up of three layers, each of which is comprised of a different material: gallium indium phosphide on top, gallium arsenide in the center, and gallium indium arsenide on the bottom. Each absorbs a particular range of light wavelengths, allowing the cell to absorb more energy from the entire light spectrum. There are also three hundred "quantum wells" in the middle layer, which were the key to unlocking the new efficiency rate of these cells. 3 These wells boosted the amount of light that the cell could absorb overall by extending the bandgap in the cell4.
NREL isn't the only one who's had success increasing energy output by modifying their solar cell design. The University of Surrey-led team enhanced the quantity of energy absorbed by their wafer-thin solar panels by 25%. The panels are only one millimeter thick, yet they have a honeycomb-like layer that facilitates light absorption. Normally, about one-third of the light that strikes a silicon cell bounces right off, but the textured architecture of these tiny photovoltaic cells holds the light in the solar cell, increasing efficiency. This design was inspired by nature – butterfly wings and bird eyes are examples of this. The team observed absorption rates of 26.3 mA/cm2, a 25% increase above the previous record of 19.72 mA/cm2 set in 20175.
The efficiency rate isn't bad either: these cells have a 21% efficiency rate, with the anticipation that additional adjustments will push that number higher, potentially even higher than other commercially available photovoltaics.
Perovskite advancements
Solar panels are typically associated with silicon (which is utilized in 95% of panels on the market today), but there has been a lingering beacon on the solar world's horizon: perovskites. I've mentioned these in earlier videos.
Perovskites are a type of synthetic material distinguished by their crystalline structure. They quickly coat surfaces in general, which implies they can be utilized in cells alone or in conjunction with other technologies (like our existing crystalline silicon cells) 6. Because these perovskite semiconductors can transform sunlight's energy-rich blue spectrum into energy, when combined with silicon sub-cells, we can achieve efficiency rates of up to 30% (compared to 25% in single-junction perovskite cells). 7.
Perovskites are supposed to be the golden trio: inexpensive to make, competitively efficient, and tiny and lightweight enough to be used almost anywhere. That's why researchers have been chomping at the bit to get them on the market, but there are a few practical challenges to overcome before perovskites can compete with silicon cells.
The first issue is one of perovskite's most significant challenges: durability. The thin and light nature of perovskite cells is a benefit, but it also means that they are fragile, which is not ideal for a material that will be subjected to rain, sun, hail, and everything in between. Previously, samples would shatter before researchers could even get them across the lab to be tested8! If the samples cannot be handled in the laboratory, they will not be able to endure the odd hailstorm or the strains imposed on the solar panel structure by wind loading and torsion in the real world.
They've come a long way since then, thankfully. An April study9 discovered that organometallic compounds could be utilized as a supplement to assist boost the longevity, efficiency, and stability of cells. After 1500 hours of usage, the improved cells retained 98% of the cell's original 25% power conversion efficiency rate, and they also passed the damp heat stability tests with flying colors.
Researchers have also been delving further into why perovskite operates the way it does, for better or worse. In May 2022, researchers from Cambridge University and Japan's Okinawa Institute of Technology (OIST) used imaging tools to study the structure of perovskite films at the nanoscale, particularly when light strikes the film. They discovered one of the villains responsible for perovskite's notorious photodegradation problem: nanoscopic trap clusters10. These are material flaws that manifest as pockets from cell processing, making the film less efficient and structurally unstable. The primary method of combating these efficiency-limiting carrier traps is to remove them during the manufacturing process through careful structural and chemical design optimization. Make these changes large-scale-friendly, and you've got a recipe for making more of these films while simultaneously improving their performance.
Solar cells made of organic materials
What if it was as simple as printing a newspaper to create fresh solar cells? That's what the makers of organic power cells plan to do, and they're ready to launch this technology into the global market right now.
Photovoltaic material is printed onto flexible materials such as plastic sheets to create organic power cells. These paper-thin solar cells are made completely of organic materials, making them flexible, lightweight, and easy to produce using printing technology (the same process used to print newspapers!). 11 They are half the price of silicon-based cells and 100 times lighter. Each square meter weighs less than two kilos, and this figure is expected to fall below one kilogram by 202312.
Unlike silicon cells, their conversion efficiency rate does not decrease when used indoors, making them particularly appealing for devices such as smart speakers, sensors, and other wearables that may not receive a lot of direct sunlight. This utilizes existing ambient light by converting some of it to electrical power, so lowering the demand on small batteries and charging gadgets.
The efficiency rate of 10% leaves something to be desired, but these cells can also be utilized for around 20 years12, which dwarfs current perovskite lifespans (more on that later). As more companies begin to increase production, mass production has the potential to slash costs in half.
These "print-to-order" solar cells are making their way onto the global market. Heliatek, a German firm, will begin mass production of organic solar cells this year, with an aim of producing 600,000 square meters (with a maximum manufacturing capacity of 1.1 million square meters per year!) Sunew, a Brazilian firm, is also making these organic cells, having so far produced over 10,000 square meters of organic solar cells for vehicle rooftops (as they are big electric-vehicle aficionados). Epishine of Sweden launched its small solar collecting modules on the market in December, touting a 13% energy conversion rate and a 10-year lifespan. These can be used for temperature and humidity sensors, fire alarms, card readers, and other small-but-important electronics that blend into the backdrop. Then there's Ricoh in Japan, which began on a smaller scale. They only produce 100 square meters every year, but that's enough to power 50,000 small smart devices, ranging from wearables to tunnel and bridge safety sensors[16].
Even these cool cells have room for improvement, and researchers have discovered two critical advances that have the ability to truly assist organic cells in capturing that spark.
Buckle up, because we're about to get nerdy in here. Let's discuss about chirality.
Chiral compounds include DNA (and other helix-shaped molecules). That design can be found all over nature and is essential to almost everything, from our genetic makeup to photosynthesis. They're asymmetrical, and as electrons pass through the lattice, they separate the charges caused by light (meaning that light can be converted into biochemicals more efficiently).
Typically, molecules stick to their own structural cliques... It's similar to high school... (For example, chiral with chiral, achiral with achiral, and so on). However, researchers at the University of Illinois Urbana-Champaign discovered that when achiral conjugated polymers were sprayed with a solvent, the solution eventually evaporated, leaving behind reassembled polymers: particularly, helixes, aka, chiral structures11.
The transition from achiral to chiral structures is significant, especially when applied to organic solar energy. In theory, scientists can apply that chiral structure (and all of its energy-producing goodness) to technologies that generally require achiral conjugated polymers to function, such as solar cells.
Second, let us discuss everyone's favorite topic: perfluorinated sulfuric acid ionomers. (No? Only me?) Let me explain: hole-transporting elements are required to create fully-printable organic solar cells. That's a hole, not a whole... You have to adore the English language. These are known as HTMs. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), a conducting polymer complex used to manufacture printable devices13, is one such promising HTM. It has been around since the 1990s, but it is now falling short. Unfortunately, it disperses in water and is very acidic, reducing the efficiency and stability of PEDOT:SS-based solar cells.
To tackle this, Huazhong University of Science and Technology and the Institute of Materials for Electronics and Energy Technology (i-MEET) researchers developed PEDOT:F, a novel polymer complex that disperses in alcohol and has a low acidity. Organic photovoltaics with this new formula demonstrated a power conversion efficiency of 15% and a retention of 83% of their initial efficiency under continual illumination at maximum power for a total of 1,330 hours13.
These new solar breakthroughs may not catch the average person's eye, but they are a clear indication that there is still more to solar energy on the horizon. So, what can we glean from these events, and what does it all signify for the industry as a whole?
Breakthrough efficiency and design
First, as thrilling as it is to beat the world record for solar efficiency, NREL's solar cell design has its own drawbacks. For one thing, building this type of cell is still going to be expensive at this stage, which is already a concern in the renewable energy business as a whole. Mass producing cells with this degree of efficiency may still be a long way off, and we'd have to figure out how to accomplish it while keeping overall costs low enough to keep major consumers out of the market.
The University of Surrey's honeycomb design, on the other hand, appears to explicitly address that issue. These cells consume less silicon overall, resulting in cost reductions during the manufacturing process. There's also a lot of flexibility in how we may utilize them: even when textured, the film layer is still incredibly thin, making them light and versatile enough to go almost anywhere!
The next step is to get the show up and running by identifying commercial partners and developing manufacturing procedures. As you might expect, that's no minor effort in and of itself, and for the time being, this design is still a long way from the market, which is an awful fate for many promising renewable technology in the works.
Perovskites
So what about perovskites, the solar industry's shining light and problem child at the same time?
Perovskite cells are now on the market, but they're nothing near where supporters imagined they'd be, and they're certainly not commercialized yet. Much of this might be attributable to their unpredictable temperament on the field. Both silicon and perovskite solar cells have lately established records exceeding 25%, indicating that power isn't always the issue: durability is.
Unfortunately, after a few months of usage, perovskite cells lose 10% of their effectiveness. When compared to silicon cells, whose manufacturers say that panels would retain 80% of their performance for up to 30-40 years, this is a difficult act to follow. To fulfill the US Department of Energy's Solar Energy Technology Office (SETO) 2030 goals of $0.02/kWh14, perovskite cells must endure at least 20 years in the field.
Manufacturing will almost certainly be the last big barrier to commercializing perovskite solar panels. It's a catch-22 situation: we need finance to scale up manufacturing and produce cells on a massive scale, but financing will only be available if the scaling up appears practical.
The good news is that perovskites do not have to outperform silicon cells. They can also be used in tandem cells, which consist of a perovskite layer placed on top of a silicon cell. (It's the best of both worlds!) Because the materials absorb distinct light wavelengths, complimentary energy harvesting occurs.
Cells of organic origin
And what about organic cells? The concept itself remains appealing. These lightweight and flexible cells may be used almost anyplace, including domed roofs, glass, and other weirdly shaped surfaces that couldn't support the heavier silicon-based panels.
These guys are unlikely to power your neighborhood anytime soon, but they have found their own niche: tiny devices, especially wearables.
What's the big deal about wearables? Most are powered by single-use batteries that must be replaced every 1-2 years. That's significant for this sector, given that the global market for smart sensors alone is estimated to reach $29.6 billion by 2026, according to MarketsandMarkets. Current solar technology is insufficient for these tiny applications since silicon does not function well indoors and perovskite cells only last a few years.
True, their efficiency rate remains a little low (at least, compared to their other solar counterparts). More research into chirality and other polymer solutions, perhaps, will help raise that efficiency rate in the long run, making the "printed solar cell" a standard in the solar community.
While we're probably still a few years away from seeing these undeniably cool discoveries make a market impact, it's a clear indication of where things are headed. However, if you're thinking of going solar for your home, don't put it off any longer. Solar panels are now efficient enough to achieve many of the goals you likely have for your home. Waiting for the next great thing almost guarantees that you'll constantly be waiting... because something better is always around the corner. If you live in the United States, don't pass up the current Federal tax solar refund, which will expire at the end of the year. You can use my EnergySage portal to conduct research and obtain quotations from local installers. I thoroughly enjoyed using EnergySage to study items and choose my own installer for my home. Don't wait and risk missing out.