Investigation of fill factor losses on 20.2% efficient n-type mono-like silicon solar cells with laser contact opening

Abstract

Large area (243.36 cm2) back-junction passivated emitter, rear totally diffused (PERT) solar cells with laser contact opening (LCO) on n-type mono-like crystalline Si with efficiencies of 20.2% are presented. Boron emitters with high electrical quality (implied open circuit voltage iVOC up to 700 mV) are formed during a co-diffusion step using SiOx:B layers. Increasing the rear metal contact coverage, we observed a decrease in fill factor (FF) instead of the expected increase due to the decrease of the back side series resistance. We show that it can be attributed to recombination centers (RCs) in the space charge region underneath the contact spots inducing an increasing second diode contribution. The presented empirical model for the RCs implemented in Synopsys Sentaurus TCAD allows for a successful reproduction of the FF, pseudo FF and VOC behaviour with contact coverage. According to this model, the RCs induced by laser ablation and subsequently evaporation of Al have a shallow exponential distribution with a characteristic length of LT = 0.2 µm and an effective surface density of N *T0 = 25 cm–1.