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Panasonic crystalline silicon solar cell conversion efficiency refresh the highest value
The cell conversion efficiency of crystalline silicon solar cells has reached a new high, marking the highest level in 15 years. As the dominant technology in the solar industry, crystalline silicon has long been the focus of efficiency improvements. Previously, the record stood at 25.0%, set by the University of New South Wales (UNSW) in 1999. Recently, Panasonic broke this record with an impressive 25.6% efficiency, as shown in Figure 1.
What makes this achievement even more significant is that Panasonic achieved this on a practical-sized cell measuring 143.7 cm², unlike UNSW’s previous record, which was based on a small 4 cm² unit. Additionally, Panasonic developed a prototype module using 72 of these high-efficiency cells, resulting in a module output of approximately 270W—25W higher than their latest commercial product.
Figure 1: Conversion efficiency exceeds 25%
**Using new structures to push boundaries**
The theoretical maximum efficiency for crystalline silicon solar cells is around 29%. Currently, achieving 25–26% is considered close to the physical limit. With Panasonic now reaching into this range, the industry is closely watching how much further efficiency can be improved. According to Panasonic's officials, their next goal is to reach 26%, and they are confident it is achievable.
This improvement comes from advanced cell designs. Historically, Panasonic used a "heterojunction" structure, where an amorphous silicon layer is deposited on a silicon wafer. This helps reduce carrier recombination, thereby increasing voltage. Electrodes were placed on both the front and back surfaces of the cell.
For the first time, however, Panasonic introduced a "back contact structure," which retains part of the heterojunction but removes the front-side electrodes. By eliminating the light-blocking front contacts, the cell can generate more current. In fact, the short-circuit current density improved compared to their earlier heterojunction design from February 2013 (Figure 2). Combining this with the high voltage from the heterojunction structure allowed them to achieve the 25.6% efficiency.
Figure 2: Implementation with a different structure than before
Note 2: Although the open circuit voltage slightly decreased, Panasonic is investigating the cause, possibly due to increased wafer thickness.
Other companies like Sharp and LG Electronics are also exploring similar technologies. Sharp, for instance, achieved 21.7% in 2012, then quickly rose to 24.7% in 2013, and later announced a 25.1% efficiency in April 2014. With multiple companies surpassing 25%, it’s clear that research in this area is accelerating rapidly.
Despite these advancements, Panasonic has not yet decided whether to implement the new structure in its products. However, the company emphasizes that "the method of improving efficiency has added a new option." They have been researching this approach for several years and finally achieved over 25% efficiency. While the potential for improvement is promising, integrating the back contact structure into production lines would require additional steps such as adding a backside patterning process or refining module manufacturing techniques.
Figure 3: Measurements in February 2014
Note 4: The heterojunction structure is symmetrical and less stressful, making it easier to thin the wafer. However, the back contact design loses this advantage. Panasonic claims they can manage stress through careful design. For now, they are not focusing on thinning and are using wafers similar to those used in mass production, with a thickness of about 150 micrometers.
Panasonic continues to invest in heterojunction cell development, stating that there is still room for efficiency beyond 25%. While the focus is currently on scaling up production, the path toward higher efficiency remains a key priority for the company.