The cell conversion efficiency of crystalline silicon solar cells has reached a new high, marking the best performance in 15 years. As the dominant technology in the solar industry, crystalline silicon has long been the focus of research and development. The previous record of 25.0% was set by the University of New South Wales (UNSW) in 1999, but Panasonic recently broke this with an impressive 25.6% efficiency (Figure 1). This breakthrough highlights significant progress in optimizing solar cell performance.
What makes this achievement even more remarkable is that Panasonic achieved this on a larger, practical-sized cell measuring 143.7 cm², compared to the small 4 cm² unit used by UNSW. Additionally, Panasonic developed a module using 72 of these cells, resulting in an output of approximately 270 W—25 W higher than their current product line. This demonstrates not only improved efficiency but also scalability for real-world applications.
The theoretical maximum efficiency for crystalline silicon cells is around 29%, so reaching 25-26% is considered near the upper limit. Panasonic's achievement has sparked interest across the solar industry, as it shows that further improvements are still possible. According to the company, the next target is to push efficiency beyond 26%, stating, “This value should be achieved.â€
To reach this level, Panasonic introduced a new structure known as the "back contact" design. This approach retains part of the heterojunction structure while eliminating the front-side electrodes, which reduces light-blocking and allows for higher current flow. While this design improves short-circuit current density compared to earlier models (as seen in Figure 2), it slightly lowers the open-circuit voltage. Engineers are currently investigating this trade-off, possibly due to increased wafer thickness.
Other companies, such as Sharp and LG Electronics, are also advancing similar technologies. Sharp, for example, achieved 21.7% efficiency in 2012 and quickly raised it to 24.7% in 2013, eventually hitting 25.1% in April 2014. These developments suggest that the race to improve solar cell efficiency is intensifying.
Despite these advancements, Panasonic has not yet decided whether to implement the back contact structure in its commercial products. However, the company emphasizes that this new method adds another valuable tool to their efficiency improvement strategy. They began researching this technology several years ago and have now successfully demonstrated over 25% efficiency (Figure 3).
While the potential for further efficiency gains is promising, integrating this technology into mass production requires additional steps, such as modifying the cell manufacturing process or enhancing the module assembly. Panasonic notes that the heterojunction structure is already well-suited for thinning, but the back contact design introduces some challenges in terms of stress management.
Currently, Panasonic continues to focus on improving heterojunction cell performance, aiming to push the boundaries of what’s possible. Although the main goal is to increase efficiency, the company is also working on refining the manufacturing process to ensure reliability and cost-effectiveness. With ongoing research and innovation, the future of solar energy looks brighter than ever.
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