At Oxford PV, a UK-based firm, something extraordinary is unfolding. With an industry-leading efficiency of 28.6%, they are on the brink of revolutionizing solar energy. All thanks to their groundbreaking work with perovskite. In early September 2024, the company made its first shipment of perovskite PV modules to the United States, a move that could change everything. But here’s the twist—Oxford PV isn’t the only player exploring the incredible potential of this mysterious material. What’s next? The world is watching, and the race has only just begun.
A Global Race for the Next Solar Breakthrough
Anyone who gets it right is on track for a potential gold mine. Laboratories worldwide are working tirelessly to develop the next big breakthrough in solar technology. A research team in China now claims to have perfected a process for producing verifiable perovskite solar PV cells with conversion efficiency surpassing the Shockley-Kweiser limit.
What Is the Shockley-Kweiser Limit?
What exactly is the Shockley-Kweiser limit? Why are solar photovoltaics constrained by it? Can the Chinese team’s claims be true? Why is it so important? Let’s dive in and explore.
Oxford PV’s Progress and Efficiency Discrepancies
Oxford PV recently announced the shipment of their 72-cell solar PV modules from their new facility in Brandenburg an der Havel, Germany, to commercial customers in the United States. However, they are now claiming a conversion efficiency of 24.5% for the final production version, a figure significantly lower than the 28.6% they previously quoted. Why the discrepancy?
Why Cell Efficiency and Panel Efficiency Differ
The answer lies in the distinction between cell efficiency and panel efficiency. While the website quotes individual cell efficiency, the shipping product is the fully assembled panel. Which is less efficient due to the effects of lining up the cells, framing, and adding protective layers. At 24.5%, the panel efficiency is still about 20% better than any other commercially available solar PV technology.
Perovskite Technology: A Major Step Forward
In a recent interview with PV Magazine, Oxford PV’s CEO David Ward described the launch of perovskite modules as a major breakthrough for the energy industry. With this technology, the solar industry is poised for a future dominated by highly efficient technologies. Oxford PV’s tandem cell technology, which combines perovskite with silicon, could potentially reach efficiencies of 43%.
China’s Cutting-Edge Research in Solar Efficiency
Now, let’s shift our focus to the latest research from a Chinese team. It comprises scientists from renowned institutions such as Nancheng University’s Institute of Photovoltaics, Hong Kong University’s Department of Applied Physics, Wuhan University of Technology, and Fudan University’s Institute of Optoelectronics. Notably, this team claims to have developed an organic coating that significantly enhances the efficiency of monolithic tandem cells made from silicon and perovskite.
Understanding Tandem Cells and the Shockley-Kweiser Limit
This brings us back to the Shockley-Kweiser limit. To understand how tandem cells can theoretically exceed this limit, we must examine how sunlight interacts with solar cell materials, particularly in terms of the wavelengths they absorb.
The Shockley-Kweiser Limit Explained
Certain semiconductors can absorb a broad spectrum of light, which is great for capturing more sunlight. However, they often generate low electrical voltage, rendering them unsuitable for solar panels. In contrast, other semiconductors can produce higher voltages but only capture a narrower range of light, leading to significant sunlight wastage. In 1961, Shockley and Kwizer determined that silicon was the optimal material, and the theoretical maximum efficiency of a single-layer photovoltaic cell was around 30%.
How Perovskite Can Break the Efficiency Barrier
Perovskite, an inorganic compound, fits into this equation by being precisely and inexpensively produced at low temperatures. Researchers can chemically manipulate it to absorb different wavelengths of light that silicon cannot. Researchers discovered over a decade ago that layering perovskite on silicon wafers allows them to absorb a broader spectrum of light while maintaining a good voltage, which could overcome the Shockley-Kweizer limit of 30%. This discovery sparked the field of tandem cell research, which is still ongoing today.
The Challenges of Stability in Perovskite-Silicon Cells
Over the past decade, a significant focus has been on improving the stability and reliability of silicon-perovskite tandem cells in real-world conditions. This has proven to be a challenging task. However, Oxford PV is leading the charge, aiming to create production-ready panels that can convert over 30% of sunlight into electricity.
The Road to 43% Efficiency
Oxford PV is confident that, in just a few years, their technology will reach the 43% efficiency mark, doubling the output of typical solar panels. This is where the Chinese research could make a significant contribution.
Innovative Manufacturing Processes for Tandem Cells
Monolithic tandem cells use silicon wafers made by a process called zone melting, which creates a polished or nanostructured surface. Another cheaper method, the Czochralski process, produces silicon wafers with micrometer-scale pyramid-like structures that capture more light.
Overcoming Defects in Perovskite Layers
The challenge arises when perovskite is added to these silicon wafers, introducing defects in the lattice structure that hinder light conversion. The Chinese researchers have developed a technique called surface passivation, which smooths out these defects, improving the perovskite layer’s ability to capture sunlight.
A Breakthrough Spray Coating Process
The Chinese team has also introduced a dynamic spray coating process. Using a complex chemical combination called fluorinated thiophenethylene ammonium with a trifluoromethyl group. This chemical is highly polar and has strong binding energy. Which allows it to fill in the microscopic gaps and defects on the perovskite surface, improving efficiency.
Impressive Results and Long-Term Stability
When researchers applied the spray-coated perovskite to a Czochralski-textured wafer. They achieved an impressive efficiency of 30.89%, which independent assessors verified. Moreover, the cells exhibited remarkable operational stability, maintaining over 97% of their original performance after 600 hours of continuous illumination.
Progress or More Lab-Based Hype?
The research paper details the molecular science behind this breakthrough, though it’s behind a paywall. Is this a step forward in improving solar PV efficiency. Or is it just another lab-based experiment with limited real-world application?
For a deeper dive into the challenges of commercializing perovskite solar cells and ensuring their durability in real-world conditions, check out our article: “The Road to Stable and Scalable Perovskite Solar Technology. To explore more about the commercialization challenges and opportunities for next-gen solar technologies, read our related article on Quantum Dots.
