At the beginning of 2023, the Viperlab project dropped videos inviting researchers to apply for free access to its perovskite solar cell material testing and device processing facilities.
The move, by the EU-backed consortium of perovskite-development linked European technical institutes, universities, and public bodies, was the latest sign of joint working by PV researchers and industry to take perovskite-silicon tandem solar to the next level.
In 2022, Qcells, Enel Green Power, Meyer Burger, and Voltec Solar all announced perovskite-silicon tandem initiatives, bringing deep process knowledge including vacuum deposition, interfacial engineering, and encapsulation methods to the table.
pv magazine has checked in with all of them, plus members of the research community and equipment supply chain, and perovskite-silicon tandem pioneer Oxford PV, to ask about progress in perovskite stability.
With researchers taking tandem cell configurations to more than 30% conversion efficiency in the lab, R&D collaboration with industry is the way forward. There have also been promising stability announcements and larger-device breakthroughs.
“Interest from industry is higher since setting the new record for perovskite tandem cells,” says Steve Albrecht, head of the perovskite tandem solar cell department at German research body the Helmholtz-Zentrum Berlin (HZB). “It’s worldwide interest. Efficiency is shown, now it is stability and scaling that need more R&D.”
Albrecht is referring to the perovskite-silicon tandem record of 32.5% efficiency set by the HZB in December 2022. In January, the institute announced an additive with promising stability performance. “There are more researchers tackling stability,” he says. “Instability factors are also becoming better understood. There is more and more data available. I expect it to continue along these lines.”
Switzerland-based Centre Suisse d’Electronique et de Microtechnique (CSEM) and the École Polytechnique Fédérale de Lausanne in July 2022 announced a 31.25%-efficient perovskite-silicon tandem device and stressed the need to scale up and reach a stable lifetime for the cell.
“The challenge is to bring the operational stability of perovskite solar cells closer to the standards achieved by silicon technologies,” says Quentin Jeangros, CSEM Group Leader for Perovskite Materials and Devices. “This will be key to making perovskite PV cost-competitive for mainstream applications.”
Gianluca Coletti agrees. He is the program manager for PV tandem technology at Dutch research body the Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek (TNO) and co-ordinates the organization’s contribution to the Solliance thin-film solar research consortium. Solliance recently achieved 30.1% efficiency with a four-terminal perovskite-silicon tandem cell.
“New stability results are reported continuously,” Coletti says. “At the beginning, reported shelf-lives were shorter than a few minutes. Today there are many withstanding 3,000 hours, and outdoor stability for over two years. A lot has been learned. Equally important are breakthroughs made in recent months with larger-area devices. Efficiencies of over 26% on larger devices – for example, greater than 20 cm2 – were achieved by at least four teams.
“However, we’re at the point, as a research community, where we need to change gear and focus on technology for up-scaling and increasing technology readiness levels. Therefore, long-term stability is one of the crucial points. Now that the 30% barrier has been smashed through, it is time to strongly focus R&D efforts on reliable devices and this is better achieved forming partnerships between industry, research institutes, and academia.”
The pioneer is Oxford PV. With a new CEO, the Oxford University spinout is ramping two-terminal (2T), monolithic perovskite-silicon tandem cells at its production line. Progress at its German plant has been hampered by equipment delivery delays but is on track to produce M6-wafer format tandem solar cells with a stable efficiency of 27% – to rise to 30% – according to chief technology officer Chris Case.
“Full size, 60-cell modules based on cells from our pilot line are being assembled by customers and partners,” Case tells pv magazine. “A respected and well-known certifying agency is assisting with the full-size module certification.”
In Italy, utility Enel’s Green Power renewables arm is working on 2T perovskite-silicon tandem technology with France’s Institut National de l’Énergie Solaire. Production is slated for 2025. In 2022, the partners announced 24.9%-efficient, 9 cm2 devices and, in December, they hit 25.8%.
“Today, tandem perovskite-silicon heterojunction (HJT) solar cells have shown efficiency above 30% at small-area level,” says Eliano Russo, head of Enel’s 3Sun solar gigafactory in Sicily. “The use of HJT as bottom cell has demonstrated to be a very suitable approach to obtain a highly efficient monolithic perovskite-silicon tandem solar cell.”
In terms of developing larger, more stable, more reliable devices, Russo adds, “We are extensively working on these aspects to be ready in a few years with an industrial product with elevated performance and reliability.”
Qcells has announced a European perovskite-silicon tandem initiative as part of the recently launched, EU and Swiss government-backed “Pepperoni” project consortium. Fabian Fertig, Qcells’ director for global wafer and cell R&D, says a pilot line at the company’s Thalheim plant, in Germany, will identify and address barriers to tandem solar cell market introduction.
“Reliability remains a key challenge for a potential commercialization of perovskite-silicon tandem solar cells and modules,” says Fertig. “While the progress in the field on improving stability and durability has been significant, there is further work required to achieve a sufficient level to be competitive with existing silicon-based products. The multi-year Pepperoni project involves 17 European collaborators … The benefits of this project will hopefully be felt by the entire European solar industry.”
In France, module manufacturer Voltec Solar is working on perovskite-silicon tandem research with the Institut Photovoltaïque d’Ile-de-France (IPVF). Their France PV Industrie joint venture is working on four-terminal technology.
“Our project aims to achieve at least a 15% reduction in the levelized cost of energy (LCOE) with this type of tandem panel, compared to current silicon panels,” says IPVF General Director Roch Drozdowski-Strehl.
Swiss heterojunction solar manufacturer Meyer Burger recently said it is working with local and German research groups to integrate perovskite tandem technology into its manufacturing.
Supply chain development
Swedish manufacturing equipment and technology business Evolar AB last year reported stability progress with 100 cm2 devices made with its evaporation-based deposition process.
CEO and co-founder Mats Ljunggren confirms commercial interest in Evolar’s turnkey production line for perovskite cells to be combined with established silicon lines. “Inquiries are coming from all over the world,” he says. “Our sales team is currently issuing quotes for pilot lines where we will provide both equipment and the services to help our customers ramp up.”
Founded in 2019, Evolar is marketing to integrated cell and panel producers and employs around 40 people, the majority of whom are process developers and equipment engineers.
Fluxim, a Swiss developer of characterization and modeling tools for emerging PV, also has insight into perovskite progress. “At the level of research and development, both in academia and industry, I think that Europe has an advantage, with many strong research groups and institutions here,” says Daniele Braga, the company’s head of sales.
“The next step is to focus on setting up manufacturing lines to keep the present pole position,” says Frank A. Nüesch, head of functional polymers at the Swiss Federal Laboratories for Materials Science and Technology. “Such a move would send signals to the extended value chain, including the chemical industry, to encourage it to work on the synthesis of high-quality chemicals required for the perovskite junction.”
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