Firing stable passivation with a-Si/SiNx stack layers for crystalline silicon solar cells

This paper describes a stack of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-SiNx:H) which was developed and characterized with the aim to obtain a firing stable passivation layer. A surface recombination velocity below 40cm s-1 has been obtained after a firing step at 820°C, on highly doped p-type Float Zone (FZ) crystalline silicon wafers. Fourier Transform InfraRed (FTIR) spectroscopy measurements showed that most of the silicon hydrogen bounds (SiH) in the a-Si:H layer are lost after firing independently of the firing stability of the passivation. Capacitance-Voltage (CV) measurements showed that the a-Si:H layer assumed to be intrinsic is, in fact, doped n-type. The measured doping of the layer might result in a field-effect passivation on lowly doped p-type silicon surfaces. However, significant shunt losses can be expected when the stack of layers is applied for rear surface passivation on p-type silicon solar cells.