Characterization and analysis of reverse breakdown voltage onset of solar cells with different cell architectures

In 2016 Passivated Emitter and Rear Cell (PERC) solar cells started to dominated the PV industry as cell technology. Since 2023, the prices of Tunnel Oxide Passivated Contact (TOPCon) and Heterojunction (HJT) solar cells have become lower, leading to a strong decline in PERC technology till today. TOPCon is now (2025) the mainstream cell technology, while HJT and BC (Back Contact) cells are gaining market share. All technologies feature different cell sizes and quantities, resulting in higher voltages, currents and different reverse characteristics compared to PERC. One major challenge in integrating these new technologies into existing module designs is understanding the reverse bias behavior of solar cells to avoid excessive overheating of partially shaded cells. Evaluating this behavior is crucial for the durability and reliability of PV modules when fully / partially shaded. In such scenarios, shaded cells operate as a load, altering current flow. If the voltage of the series-connected cells exceeds the reverse breakdown voltage of a single cell, that cell can undergo electrical breakdown in reverse bias, consuming energy produced by the other cells. Excessive heat generation due to defects can lead to hot-spots, melting of encapsulants or solder, glass breakage, and even fires. Given the trend toward larger cells (G12, M10) and higher cell quantities (more than 20) for increased module power, a reevaluation of the breakdown behavior of solar cells is urgently needed. To properly understand the behavior of new solar cell technologies in the market, all major architectures were evaluated. Mini-modules were manufactured with the different cell architectures and characterized in forward and reverse bias. The cells/mini-strings were measured at irradiance levels from 100 to 1300 W/m2 in the 1st quadrant all the way to reverse breakdown in the 2nd quadrant. This was especially challenging for HJT and TOPCon cells as they have a pronounced hysteresis effect in the 1st quadrant. However, neither TOPCon nor HJT shows an accountable hysteresis in the reverse breakdown region. As both technologies are bifacial, the behavior is not significantly different between front and rear side. Besides the higher breakdown voltages, −44 to −49V and around −30V for TOPCon and HJT, respectively, their irradiance dependent reverse current increase is compared to PERC low to very low. The results of TOPCon and HJT solar cells show a promising reverse breakdown behavior even with strings with higher number of solar cells under full and potentially also under partial shading conditions.