Further Studies on the Effect of SiNx Refractive Index and Emitter Sheet Resistance on Potential-Induced Degradation

Abstract

We present the impacts of silicon nitride (SiN x ) antireflection coating refractive index and emitter sheet resistance on potential-induced degradation of the shunting type (PID-s). Previously, it has been shown that the cell becomes more PID-s-susceptible as the refractive index decreases or the emitter sheet resistance increases. To verify the effect of refractive index on PID-s, we fabricated cells with varying SiN x refractive index (1.87, 1.94, 2.05) on typical p-type base solar cells with ∼60 Ω/sq emitters. However, none of these cells showed output power degradation, regardless of the refractive index. Further investigation of the emitter showed that the PID-s was suppressed at ∼60 Ω/sq due to the extremely high surface phosphorus concentration (6 × 1021 cm−3), as measured by secondary ion mass spectrometry. Furthermore, PID-s was observed on cells possessing a high emitter sheet resistance (∼80 Ω/sq). The emitter surface phosphorus concentration plays an important role in determining PID-s susceptibility.