Impact of the homogeneous junction breakdown in IBC solar cells on the passivation quality of Al₂O₃ and SiO₂: Degradation and regeneration behavior

Within the last years, many different approaches for the simplified fabrication of interdigitated back-contact (IBC) solar cells have been developed. Most of those concepts result in emitter and back-surface field (BSF) regions that are in direct contact to each other which leads to a controlled breakdown under reverse bias at the p⁺n⁺ junction. In this work, the influence of the reverse breakdown on the passivation quality of Al₂O₃ and SiO₂ at the p⁺n⁺ junction is investigated, not only shedding light on the degradation but also on the regeneration behavior of the cells. It was found that cells with Al₂O₃ passivation on the back side degrade during reverse breakdown whereas sister cells with SiO₂ passivation were rather unaffected. Consequently, the degradation seems to be related to the passivation layer. However, it is shown that the passivation can be regenerated even under normal operation condition. A possible explanation is the discharging of interface traps, which are getting recharged already at room temperature.