A Chinese module manufacturer has led an international research team to save silicon material and increase efficiency in the development of heterojunction PV devices. The cell achieved a certified power conversion efficiency of 26.06% with a thickness of 57 μm, and the German Institute for Solar Energy Research confirmed the result.
March 4, 2024 by Valerie Thompson
From Global pv magazine
Researchers continue to push the boundaries of silicon solar cell technology to use less material in thinner and lighter cells without sacrificing efficiency and durability.
Now, a team led by researchers at Chinese vertically integrated module maker Longi has developed processes for producing highly efficient heterojunction (HJT) solar cells, avoiding the brittleness and low efficiency results seen in previous attempts to produce thinner cells.
In the study, “Flexible Silicon Solar Cells with High Power-to-Weight Ratio,” published in Nature, the scientists report that the new cell is between 57 μm and 125 μm thick and uses M6 wafers with an area of 274.4 cm2.
Wafer thinning not only reduces weight and cost, but also facilitates charge migration and separation, the research team noted.
“The flexible and thin profile of these solar cells opens up new possibilities for incorporating solar energy generation into various aspects of daily life and industry in portable electronics, integrated PV, transportation, space applications, and emerging technologies with unconventional surfaces or structures,” – Xixiang Longi R&D Group Leader and Corresponding Author Xu told pv magazine.
The group has developed its own control and regulation system to enable a continuous low damage plasma chemical vapor deposition (CVD) process to prevent epitaxy and maintain surface uniformity. This is a modification of the traditional step-by-step, discontinuous CVD process for passivation, the researchers noted.
In addition, they performed a “vertical growth process for self-healing nanocrystal seed and doped contacts” in a high-frequency plasma-enhanced CVD (PECVD) process, which enables high-quality n-type and p-type carrier growth. selective contacts” for hole-carrying layers and electron-carrying layers.
Another innovation was to use non-contact laser transfer printing to place the low shadow grid lines. For their transparent conducting oxide (TCO) layers, they chose cerium-doped indium oxide (ICO) and a low-damage reactive plasma deposition (RPD) process.
The team deposited ICO as a TCO coating using a low-damage reactive plasma deposition method, which they said “includes lower resistivity (2.7 × 10−4 Ω cm) and higher carrier mobility (83.1 cm V−1 produced superior electrical performance. s −1), compared to indium tin oxide obtained by magnetron sputtering reported elsewhere,” adding that the process “plays a crucial role in improving subsequent stability.”
The cell achieved a certified power conversion efficiency of 26.06% with a thickness of 57 μm, a value of 26.56% with a thickness of 106 μm, and a maximum efficiency of 26.81% with a thickness of 125 μm. The 57 μm solar cell had the highest power-to-weight ratio (1.9 W g−1) and open-circuit voltage (761 mV).
The results were confirmed by the Institute for Solar Energy Research in Hamelin, Germany.
The scientists were also able to reduce optical losses by optimizing the configuration of grid lines using “industry-grade contactless” laser transfer printing technology. “The width of the finger can be reduced from 40 μm (typical screen printing) to 18 μm, with a shadow area of less than 2%,” they said.
According to the paper, the devices were tested for potential induced degradation and light-induced degradation. “This technological advance provides a practical basis for the commercialization of flexible, lightweight, inexpensive and highly efficient solar cells, and the ability to bend or fold crystalline silicon solar cells for travel is expected,” the team concluded.
The team included researchers from Jiangsu University of Science and Technology and Curtin University.
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