Phosphorus-doped Amorphous Silicon Nitride Films Applied to Crystalline Silicon Solar Cells

Abstract

The Photovoltaics Group at the Universitat Politècnica de Catalunya is investigating silicon carbide (SiC) for the electronic passivation of the surface of crystalline silicon solar cells. The doping of SiC passivation layers with phosphorus resulted in a clear improvement of the minority carrier lifetime compared to undoped SiC films applied on p-type doped substrate wafers. In a further approach, the passivation layers simultaneously served as a doping source in order to create an emitter in the underlying p-type doped silicon substrate. The aim of this Master Thesis is to establish a process for growing silicon nitride (SiN) on p-type doped crystalline silicon substrates from Plasma Enhanced Chemical Vapor Deposition (PECVD). Photoconductance measurements on the samples analyse the passivating behaviour of the SiN films. The passivation layers are doped by adding phosphine to the process gas, and further measurements investigate the effect of doping on the carrier lifetime. Furthermore, a thermal treatment initiates the diffusion of phosphorus in order to create an emitter in the substrate underneath. Sheet resistance (Rsq) and the lower limit of the emitter saturation current density (J0e) deduced from lifetime measurements, characterise the quality of the emitters. Eventually, a cell prototype finishes this work integrating both concepts of using SiN as a passivation layer, and of diffusing an emitter from the very same SiN layer.