Front surface passivation for industrial-type solar cells by silicon oxynitride - silicon nitride stacks

The ongoing reduction of wafer thickness and new solar cell concepts like selective emitters which make use of lowly doped emitters lead to the need for an improved front surface passivation of n-type emitters. Within this study a newly developed passivation stack system consisting of a bottom silicon oxynitride layer and a silicon nitiride capping layer for the front side phosphorous emitter of crystalline silicon solar cells is presented. The stack layers are deposited by an industrial-type plasma-enhanced chemical vapour deposition system. It is shown that the stack is firing stable and that the surface passivation can be improved compared to a single layer silicon nitride antireflection coating by using the developed double-layer system. On the other hand the used silicon oxynitride shows a non-negligible light absorption leading to a reduced short-circuit current density. The overall effect on the performance of a solar cell and a solar module is estimated and illustrates that especially the solar module performance can benefit from the passivation stack.