Characterization of rear-side potential-induced degradation in bifacial p-PERC solar modules

Abstract

Bifacial solar modules are increasingly preferred over monofacial modules to maximize the solar power output within a limited space. Owing to their high efficiency and compatibility with existing production lines, bifacial p-type passivated emitter and rear contact (p-PERC) solar modules have dominated the market since their commercialization. This study analyzes the influence of Al2O3, a passivation layer of p-PERC solar cells, on the PID and its underlying mechanism. Experiments were conducted on bifacial p-PERC module samples to analyze their electrical properties. Additionally, cell-like samples were fabricated to measure characteristics, for example, carrier lifetime, that are difficult to assess in full modules. To accelerate module degradation, experiments were conducted at 85 °C and 85 % humidity, while a voltage of −1000 V was applied to investigate the PID phenomenon. The results reveal degradation at the rear of the module caused by polarization effects, which were confirmed through changes in solar cell parameters and recombination current. The proposed mechanism indicates that the degradation in bifacial p-PERC solar modules is caused by the field-effect deterioration of the Al₂O₃ layer caused by alkali ions diffusing from the glass. This is observed through changes in the carrier concentration within Si and the detection of alkali ions within Al2O3. Our analysis considers both module and cell structure samples to delineate the influence of Al2O3 on the PID, which has not been previously reported. This study enhances the understanding of the polarization effect in bifacial p-PERC solar cells, thus contributing to the advancement of solar cell passivation strategies.