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What is the Most Efficient Solar Cell Out There Today?

Despite the fact that the sun only shines sometimes, solar energy has proven to be a viable alternative to beautiful, beautiful coal and other fossil fuels. Total solar PhotoVoltaic (PV) capacity in the United States reached 64.2 gigawatts in 2018, enough to power 12.3 million American homes (or most of Southeast Asia). Part of the explosive growth has been thanks to the Solar Investment Tax Credit enacted back in 2006. Advances in solar cell technology, particularly by improving their efficiency to convert light into electricity, has also been key for powering a U.S. solar industry that employs more than 242,000 people. That got us to wondering: What is the most efficient solar cell out there today?

A Brief History of the Solar Cell

The photovoltaic effect was discovered by 19-year old Edmund Becquerel while screwing around in his dad’s Paris lab in 1839. He was building a type of battery using two silver-coated platinum electrodes immersed in a dilute acid. While one was kept shaded, the other was exposed to sunlight. Becquerel observed that the “two electrodes altered their electric power.” A few decades passed before additional experiments showed that illumination could produce electric power in certain materials like selenium. In 1883, a New Yawker named Charles Fritts invented the first solar cell panel by coating “selenium with an extremely thin layer of gold, so it was transparent to light.” He achieved a whopping 1% to 2% efficiency, despite the fact that he had no idea what he was doing.

Growth of the U.S. solar industry.

It wasn’t until Albert Einstein entered the picture that the PV effect was better understood. American engineer Russell Ohl patented the first solar cell made of silicon in 1941, though we had to wait until the mid-1950s before solar cell efficiency started to inch past 2% efficiency.

The Most Efficient Solar Cell Out There Today

Solar cell efficiency simply refers to the amount of electricity produced in watts divided by the amount of solar energy it absorbs. Companies like SunPower (SPWR), LG Solar (066570:KS), First Solar (FSLR), and Panasonic (6752:JP) are among the manufacturers producing the most efficient commercially available solar panels today. The best of the best can hit somewhere between 20% and 23% efficiency, with the general consensus among analysts being that SunPower produces the most efficient commercially available solar panels today. We’ve covered the company before, as it appears on the Guggenheim Solar ETF (TAN) portfolio and is using artificial intelligence to make better PV cells.

You may have noticed our recurring “commercially available” caveat. That’s because there are more efficient solar cells out there today, but they’re not commercially available. Yet.

A couple of years ago, scientists designed a prototype solar cell that stacked multiple cells into a single device that captured nearly all of the energy in the solar spectrum, resulting in 44.5% efficiency. Basically, the device used lenses to concentrate sunlight onto tiny, micro-scale solar cells, acting sort of like a “sieve for sunlight, with the specialized materials in each layer absorbing the energy of a specific set of wavelengths.” It’s pretty cool, but pretty expensive to scale at this time.

Alta Devices proposes using its highly efficient solar cells for specialized applications.

Alta Devices proposes using its highly efficient solar cells for specialized applications. Credit: Alta Devices

A Silicon Valley company called Alta Devices, which was acquired in 2013 by a Chinese holding company that specializes in alternative energy, has produced a solar cell with a record 29.1% efficiency. Its solar cell uses a material called gallium arsenide. Gallium is a soft, silvery metal used in various electronics. Gallium arsenide has several unique characteristics that make it ideal for solar cell technology, according to Alta Devices, including high efficiency, excellent UV and radiation resistance, flexibility, and low weight. However, the technology is being targeted for specialized applications, such as small satellites, autonomous unmanned aerial vehicles, electric vehicles, and autonomous sensors. The Alta Devices solar cell is currently being tested aboard the International Space Station for possible use in future NASA low-Earth orbit missions, including powering CubeSats.

A PV technology with more immediate commercial promise for boosting solar cell efficiencies beyond the limits of silicon relies on a material called perovskite.

What is a Perovskite Solar Cell?

Perovskite refers to any crystalline material with a very particular structure, taking its name from a mineral in the Ural Mountains that was named after a Russian scientist called L.A. Perovski. The raw materials and fabrication processes are relatively cheap, while the crystalline structure is well suited for sucking the most possible light with just a thin film.

The crystalline perovskite structure is well suited for capturing light.

The crystalline perovskite structure is well suited for capturing light. Credit: Swift Solar

In other words, perovskite solar cells are cheap, highly efficient, thin, lightweight, and flexible – a potentially winning combination for the next generation of solar cells. And the technology has advanced rapidly. After Japanese scientists developed the first perovskite-based solar cell in 2009, researchers created the first stable thin-film perovskite solar cells with efficiencies of more than 10% by 2012.

The Most Efficient Perovskite Solar Cell Out There Today

Click for company websiteSix years later, a company out of Oxford, UK, called, creatively enough, Oxford PV, set a world record of 28% efficiency for its perovskite-silicon tandem solar cell. Founded in 2010, Oxford PV has raised about $99 million, including a $41 million Series D last month led by a Chinese wind turbine manufacturer, Goldwind (no doubt a subsidiary of Goldfinger). Just a few days later, Swiss solar company Meyer Burger took an 18.8% stake in Oxford PV in exchange for installing a production line in the company’s manufacturing facility in Germany, making it the biggest shareholder in the startup, Greentech Media reported. Obviously, there’s a lot of confidence in Oxford PV’s technology, which involves coating a traditional silicon cell with a thin layer of transparent perovskite, enabling it to capture more of the visible light spectrum. Some big brains out there believe Oxford PV can eventually push past the 30% efficiency ceiling.

Other Startups Developing Perovskite Solar Cells

While Oxford PV appears to have the inside track on commercializing a perovskite-based solar cell, it’s not the only startup trying to get to market. Here are a couple more companies trying to generate more electricity from the sun using the new technology.

Click for company websiteFounded in 2017, Swift Solar out of Golden, Colorado took in $4.6 million last December, according to a SEC filing. While there’s not much information about the company or its current activities, Swift Solar co-founder Sam Stranks said in a TED presentation back in 2016 that it’s possible to create perovskite cells that are colorful, semi-transparent or opaque, which means the solar panels can become an integral part of a building’s design. Some of the perovskite-based solar cells developed during the founders’ academia days are so lightweight that they can be suspended on a soap bubble.

Choose your color. Perovskite solar cells can be used as part of a building's aesthetics.

Choose your color. Perovskite solar cells can be used as part of a building’s aesthetics. Credit: Swift Solar

Let’s hope that bubble doesn’t burst like it did for an Australian company called Greatcell Solar, which had attempted to commercialize a perovskite-based solar cell before recently entering Australia’s version of bankruptcy proceedings.

Click for company websiteFounded in 2014, Polish startup Saule Technologies has raised an undisclosed amount of funding based on research by one of its co-founders who created a novel, low-temperature processing method for perovskite solar cells. Specifically, the perovskite panels are produced using an inkjet printer:

The technique allows the company to produce flexible, customized solar panels. Skanska – the fifth largest construction company in the world – has exclusive rights to use Saule Technologies’ solar cell solutions in construction and development projects, and recently implemented it in one of their Warsaw office projects. According to Skanska, “the first pilot production facility is scheduled to be launched at the end of 2019 ,which would allow for the fabrication of large perovskite PV modules on an industrial scale.” Saule also deployed their technology at the “world’s first robot hotel” in Japan, the one which ended up firing half their robot staff at the beginning of this year.

Nanotechnology for Making Efficient Solar Cells

Click for company websiteWe’re all about nanotechnology here at Nanalyze, so we had to check out one last startup that says it can reach 90% efficiency with its solar panel technology, which relies on carbon nanotubes, a topic we wrote about extensively a few years back. In this case, the carbon nanotubes act like an antenna, but collect light rather than radio waves, converting it into electricity. The technology is based on a 1960s invention – the rectifying antenna – which is used in radio frequency identification tags, PV Magazine reported. The carbon nanotubes allow NovaSolix to capture a much broader portion of the electromagnetic spectrum. The company claims 45% efficiency is within reach, while future iterations could theoretically double that.

Conclusions

Despite tariffs and other challenges that have blunted the market a bit over the last couple of years, the solar industry has experienced incredible growth, with a healthy startup scene. The latest R&D to boost solar cell efficiency could be the catalyst to reignite that dynamic growth, especially with new technologies like perovskite-based materials promising lower production costs. Oxford PV appears to be the front-runner to reach commercial scale in the next year or two, so we won’t have to wait long to see the dawn of a new day for solar energy.

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