Researchers at Zhejiang University have taken a detailed look at how impurities and structural defects limit the performance of solar cells made from mono cast silicon (CM-Si), concluding that only about 70% of CM-Si cells can achieve efficiencies on par with standard Czochralski (Cz-Si) wafers. Their findings underscore why cast-mono silicon, despite lower production costs and resistance to boron-oxygen defects, still struggles to gain commercial traction in the PV industry.
Mono cast silicon—also known as seeded cast, quasi-mono, or cast-mono crystalline silicon—is produced using a modified multicrystalline casting furnace, allowing manufacturers to create “mono-like” wafers without investing in the expensive ingot-pulling equipment required for Cz-Si. The material is inherently less prone to light-induced degradation, yet its adoption remains limited due to unresolved problems appearing later in the manufacturing chain.
Lead author Shuai Yuan told pv magazine that the team approached the issue from a practical production perspective, examining an entire ingot rather than focusing solely on idealized wafer samples. The researchers identified two dominant factors behind efficiency losses: dislocation clusters, which tend to form near the top of the ingot, and metal contamination, largely introduced through crucible diffusion. According to Yuan, dislocation clusters pose the most serious risk, driving the “efficiency tailing” that brings down the performance of roughly 30% of cast-mono wafers.
In their paper, titled “Analysis and impact of impurity defects on efficiency and stability of mass-produced cast monocrystalline silicon wafers and solar cells,” published in Solar Energy Materials and Solar Cells, the team emphasized that persistently high defect densities remain the main obstacle preventing CM-Si from becoming competitive with Cz-Si in large-scale PV manufacturing.
The researchers tested PERC cells using a metal wrap-through (MWT) architecture on a commercial Cz-Si production line. They employed photoluminescence (PL) imaging to locate regions of wafers with active recombination defects and used electroluminescence (EL) to evaluate the resulting cell performance. Their analysis confirmed that while most cast-mono wafers behave similarly to their Czochralski counterparts, the remaining portion suffers from significant defect-driven performance reductions. Yuan noted that metal diffusion and defect accumulation at the top of the ingot continue to be inherent limitations of the casting process.
He added that top-tier manufacturers in China are now shifting attention to n-type TOPCon and heterojunction technologies, both of which require extremely high-quality wafers with long carrier lifetimes. At the same time, substantial research is flowing into perovskite and tandem cell development, making it even harder for cast-mono silicon to secure a meaningful market position unless its lingering defect challenges can be resolved, despite the material’s relatively low growth costs.
Zhejiang University has a longstanding research interest in this field. In 2022, another team at the institution introduced a fabrication technique aimed at producing high-quality CM-Si ingots with stable monocrystalline fractions. Historically, companies have reported notable results with cast-mono technologies; for instance, Canadian Solar achieved 22.8% efficiency on its p-type multicrystalline P5 cell in 2019, while GCL Systems Integration announced modules with 18.9% efficiency based on cast-mono technology earlier that same year.
The new study reinforces a key theme shaping today’s Energy News landscape: progress in silicon materials is increasingly defined not just by peak efficiency, but by the ability to control defects, stabilize manufacturing processes, and meet the demands of next-generation solar technologies.