Investigation of polysilicon passivated contact's resilience to potential-induced degradation

Abstract

We present clear evidence of excellent resilience to potential-induced degradation (PID) from polysilicon passivated contacts implemented on the rear of n-type solar cells. Under the stress conditions of −1000 V, 50 °C, 30% relative humidity with aluminum foil, no damage was caused to the passivated contact consisting of an ultrathin silicon oxide (SiOx) film and an n+-doped polysilicon (poly-Si) layer after 168 h. With +1000 V bias and under the same chamber conditions, the SiOx/poly-Si (n+) passivated contact showed a slight change that translated into about 1% module power loss after 168 h, which is significantly lower than the 5% threshold recommended by IEC 62804-1 PID test standard. Furthermore, the SiOx/poly-Si (n+) passivated contact, even when encapsulated with ethylene-vinyl acetate copolymer films having a low volume resistivity in the range of 5 × 1014 Ω⸱cm, exhibited good stability under high-voltage stress. The experimental results were also validated by a generic device simulation, where the SiOx/poly-Si (n+) stack was shown to be immune to the surface polarization effect. In addition, a promising cell-level solution (i.e., using a stack of aluminium oxide and silicon nitride) to the polarization-type PID for n-type passivated emitter rear totally diffused silicon solar cells was also demonstrated.