Perovskites can make solar panels more efficient than silicon alone

Startup Caelux is betting that its ​“tandem” solar technology, which combines perovskite photovoltaics with market-dominating silicon, will result in more efficient solar panels — and the company recently received a $12 million investment from Indian conglomerate Reliance New Energy to commercialize this new approach. Vinod Khosla, no stranger to next-generation solar, is also an investor in the Caltech spinout, which is based in Pasadena, California.

Tandem solar startups like Caelux place a light-absorbing layer made from perovskites, a class of crystalline materials, atop a conventional silicon cell. This dual-material architecture has the potential to break through the efficiency barrier of single-junction silicon because of the different wavelength sensitivities of silicon and perovskite materials.

In the last 10 years, the average conversion efficiency of commercial wafer-based silicon modules has increased from about 15 percent to more than 20 percent and is forecast to reach efficiencies of 23 to 24 percent by the end of the decade, approaching the practical limits of this technology.

With a perovskite layer added, ​“you’re going to see a 20 percent to 30 percent relative efficiency boost,” Caelux CEO Scott Graybeal told Canary Media. ​“So you’re talking about modules that will come out at 27 percent to 29 percent efficiency.”

With more efficient solar panels, more electricity could be produced from a plot of land or a rooftop, making solar power — already the cheapest form of electricity in history — even more cost-effective.

But a commercially viable, higher-efficiency non-silicon solar module has proven elusive. Over the last decade, tens of billions of dollars in venture and corporate funding has been spent chasing that goal, most of it for naught.

Pros and cons of perovskites

Scientists have been researching perovskite technology for years, but recent advancements are raising excitement about the potential for tandem modules at commercial scale.

Earlier this month, researchers in the Netherlands announced a breakthrough with a perovskite-silicon tandem cell that reached 30 percent efficiency, which they called ​“a big step in accelerating the energy transition.” Other research laboratories have been announcing milestones as well.

Perovskites have some promising traits:

• The rate of hero-experiment efficiency gains for perovskite materials and tandem structures has been phenomenal, outpacing other technologies.
• Perovskites can be produced from earth-abundant materials. 
• Perovskites have the potential to be recycled. 
• Perovskite cells can be manufactured using lower-cost and more forgiving ink-based printing processes rather than complex semiconductor equipment.
• The low-temperature processes used in manufacturing perovskites mean that energy payback times are shorter than for state-of-the-art PV technologies, according to Graybeal.

But questions loom about perovskite lifetimes, degradation and stability.

Demonstrating the long-term reliability of a tandem cell will take years, as will gaining a good understanding of perovskites’ failure modes and degradation paths. Perovskites will have a ​“slightly higher degradation rate than silicon” in the material’s early days in solar tandem modules, according to Graybeal.

“To be competitive in the marketplace, perovskite’s long-term durability must be tested and verified,” the U.S. Department of Energy said in 2020 when it announced $20 million in funding to advance perovskite solar photovoltaic technologies. Earlier this year, pv magazine noted that effective testing of perovskites is not yet on track: ​“Much testing is required, yet today’s tests are geared toward commercialized PV technologies (Si, CdTe, etc.) and are unlikely to capture all the failure modes relevant to perovskite modules in the field.”

Working with, not against, silicon

Competing against silicon is an uphill battle. More than 200 gigawatts of solar power capacity will be deployed around the world this year, the vast majority of it in the form of silicon PV panels. Silicon’s long-term behavior and failure modes are already well understood, allowing module producers to offer 25-year guarantees.

So for now, most perovskite solar companies are focused on producing tandem products that include silicon, not on head-to-head competition.

While Graybeal does envision a future that includes pure perovskite modules, he acknowledges that the only way to deploy this technology at scale ​“is by combining perovskites with silicon solar” and complementing the existing PV manufacturing infrastructure.

“We consign glass [from customers] that they’ve already spec’d and qualified for their product. [We] put our proprietary material stack on that glass and then move it along to their module manufacturing operations,” Graybeal explained. He said the perovskite factory has to be close to a major logistics node and close to a customer’s module manufacturer in order for this to work, ​“and that’s been part of our plan. As much as the perovskite is part of our product portfolio, the ability to ramp and scale factories is also a competency that we’re developing.”

Caelux investor Reliance New Energy, a subsidiary of Reliance Industries, India’s largest private-sector company, is entering a strategic partnership with the startup. Reliance New Energy is building a global-scale solar factory in Jamnagar, Gujarat, where it plans to incorporate perovskites into some of the modules it produces. According to Graybeal, the partnership means that ​“Reliance has essentially sold out our factory for the first year and a half of its operation — and that’s more important than the cash investment.”

“If you’re going to get any product into the market, you have to start producing in volume. We can’t all sit around and play with our two-inch-by-two-inch devices — it will take us 10 years to get to the next technological leap forward,” said the CEO. He added, ​“Tier 1 manufacturers are going to put us through our paces before they’re going to put their name on a module with our technology on it.”

With typical entrepreneurial fervor, the CEO said he expects Caelux’s tandem module, along with a 25-year warranty, to launch into the marketplace in the second half of 2024.

Perovskite contenders

Caelux is not the only company in this space. Canary reported last year on CubicPV, formed from the merger of U.S. wafer maker 1366 Technologies and Hunt Perovskite Technologies, which is also working on tandem modules. That article listed other startups that are developing perovskite and tandem solar materials using a range of device architectures and manufacturing processes.

• BlueDot Photonics uses​“continuous flash sublimation production” techniques to improve the efficiency of perovskite photovoltaics. 
• Energy Materials Corp. is developing a roll-to-roll perovskite deposited on a flexible substrate.
• Microquanta Semiconductor is building panels from glass-packaged perovskites.
• Oxford PV is developing perovskite-on-silicon tandem solar cells and modules. 
• Saule Technologies is developing an inkjet printing technique for manufacturing perovskite solar cells packaged on bendable plastic.
• Swift Solar stacks perovskite solar cells to make tandem cells and can deposit its perovskite layers on flexible substrates and foils.
• Tandem PV aims to monolithically print thin-film perovskites on glass panels and mechanically stack them on top of silicon cells.
• Wuxi UtmoLight claims to have achieved a Japan Electrical Safety & Environment Technology Laboratories–certified 18.2 percent efficiency for its large-area 756 cm² perovskite solar module. The Chinese company says that it is conducting trial runs on its 150-megawatt module production line, which it claims is the ​“world’s largest” for perovskite solar. 

Other very early-stage perovskite startups include Beyond Silicon, MujiElectric, SoFab Inks and Verde Technologies.

But for now, perovskites still have zero percent of the global solar market share.