Asier Ukar, Director of PI Berlin Spain, discusses the importance of addressing the risks associated with Tunnel Oxide Passivated (TOPCon) technology at an early stage, even though it is better (Passivated Emitter Back Contact (PERC), given standard and concrete indicators).
Chinese manufacturers have made significant investments in this cell technology, and investors, independent power producers (IPPs) and funds are already getting to know its potential. One factor contributing to TOPCon’s success story is its price, which has fallen to about €0.01 ($0.01)/W more than PERC over the past two years.
TOPCon outperforms PERC in several “tangible” indicators, including bifaciality factor, efficiency, temperature coefficients, and annual degradation. Thus, financing models based on TOPCon show a more attractive return on investment compared to PERC. Asier Ukar, director of PI Berlin’s Spanish headquarters, says that this is often the primary factor in choosing TOPCon technology.
However, Ukar points out that it is important not only to rely on information from data sheets, but also to conduct a thorough and open analysis of the technology’s long-term behavior, especially with regard to degradation mechanisms. According to Ukari, it is very important to identify potential risks related to TOPCon technology and to address them in time.
One particular risk identified by PI Berlin relates to the presence of aluminum in the cell-to-cell contacts, which are located at the front of the cell, where moisture collects. Damp heat testing and subsequent electroluminescence testing can detect this problem. TOPCo cells are more sensitive to water vapor, so it is recommended to use polyolefin elastomer (POE) on the front side for glass-to-glass modules, while POE on both sides is better for glass-to-backplane modules.
Another risk arises from the pressure to reduce the amount of silver in the busbars of TOPCon cells, which leads to thinner busbars and a weaker grip on the cell. This can lead to mechanical damage to the print and breakage or breakage of the fingers, resulting in reduced performance due to increased effective series resistance. Electroluminescence tests can detect these problems.
TOPCon technology also has degradation challenges similar to PERC technology, such as polarization-induced degradation (PID-p). This phenomenon may affect the front side of TOPCon cells, which has a similar structure to the back side of PERC.
In addition, the aluminum oxide passivation layers of TOPCon cells are susceptible to UV degradation. While PERC technology is not significantly affected because the aluminum is on the back, TOPCon is more sensitive because the aluminum oxide passivation layers are located on the front exposed to light.
Ukar notes that during TOPCon manufacturing, it is necessary to adjust quality control, including sample size and specific tests in the laboratory, to address the risks associated with TOPCon technology. Long-term tests such as moist heat, thermal cycling or moisture freezing are crucial to evaluate the long-term reliability of the modules in addition to the standard data specified in the technical data.
In the bill of materials (BOM) of TOPCon modules, the encapsulant is a key component. Insufficient or poor quality encapsulant can negate TOPCon’s advantages over PERC. PVEL’s 2023 scorecard, which includes the PID192h test, shows significant differences in extended durability results between different product parts, even within the same manufacturer.
Ukar notes that some manufacturers relax TOPCon’s acceptance and rejection criteria compared to PERC to minimize yield loss and maintain productivity. However, it is critical to identify and address these risks early and with industry transparency in order to reap the full benefits of TOPCon.
Despite the risks involved, properly manufactured TOPCon modules exceed PERC and have minimal degradation phenomena.