Effects of passivation configuration and emitter surface doping concentration on polarization-type potential-induced degradation in n-type crystalline-silicon photovoltaic modules

System voltages can cause significant degradation in photovoltaic modules. Polarization-type potential-induced degradation (PID) is accompanied by decreases in the short-circuit current density and the open-circuit voltage. The system voltage causes a polarization and surface charge accumulation, increasing the interface recombination. The surface passivation and the emitter doping concentration and gradient are considered to have large impacts. However, a systematic study on these effects has not yet been performed. In this paper, the effects of the front surface structure of n-type passivated emitter and rear totally diffused cell modules were investigated by accelerated PID tests. Standard cells with thin silicon dioxide/80-nm silicon nitride (SiNx) antireflection/ passivation layers, refractive index (RI) of 2.0, exhibited typical polarization-type PID. Cells with increased RI = 2.4 for the bottom 20-nm SiNx showed no degradation at all. This may be caused by reduced charge accumulation in the SiNx layer near the interface due to the higher electrical conductivity of the Si-rich bottom layer. Secondly, cells with both a highly distorted interface, due to nitrogen insertion in the silicon surface, and an emitter with a high surface doping concentration have excellent resistance to PID. Cells with either the highly distorted interface or the higher emitter-surface doping concentration show no to minor improved resistance to PID. These findings improve the understanding of the effects of the front surface structure of cells on the polarization-type PID and may contribute to the implementation of these measures to reduce PID.

Automated summary

System voltages can lead to significant degradation in photovoltaic modules, particularly in the form of polarization-type PID. The front surface structure of n-type passivated emitter and rear totally diffused cell modules can impact the resistance to PID, with higher refractive index SiNx layers or highly distorted interfaces showing improved resistance. Proper surface design and emitter doping concentrations can help mitigate PID effects in photovoltaic cells.