Passivation at the interface between liquid-phase crystallized silicon and silicon oxynitride in thin film solar cells

The passivation quality at the interface between liquid-phase crystallized silicon (LPC-Si) and a dielectric interlayer (IL) was investigated in terms of the defect state density at the IL/LPC-Si interface (D-it) as well as the effective fixed charge density in the IL (Q(IL, eff)). Both parameters were obtained via high-frequency capacitance-voltage measurements on developed metal-insulator-semiconductor structures based on a molybdenum layer sandwiched between the IL and the glass substrate. Dit and QIL, eff were correlated to the open circuit voltage (V-oc) and the integrated external quantum efficiency (J(sc, EQE)) obtained on corresponding solar cell structures as well as to Voc and Jsc, EQE results based on two-dimensional simulations. We found that Dit was reduced by one order of magnitude using a hydrogen plasma treatment (HPT) at 400 degrees C. Irrespectively of the HPT, Q(IL, eff) was> 10(12) cm(-2.) We suggest that field-effect passivation dominates chemical passivation at the IL/n-type LPC-Si interface. We attribute the significant enhancement of V-oc and J(sc, EQE) observed after HPT on n-type LPC-Si solar cells mainly to improvements of the passivation quality in the n-type LPC-Si bulk rather than at the IL/n-type LPC-Si interface. For p-type absorbers, the HPT did not improve V-oc and J(sc, EQE) significantly. We propose that this is because of an insufficient passivation of bulk defects by positively charged hydrogen, which dominates in p-type silicon, in combination with an insufficient interface passivation. Copyright (C) 2016 John Wiley & Sons, Ltd.