For MIS inversion layer solar cells, PECVD silicon nitride is used as charged dielectric and antireflection layer. It was found that plasma damage occurring at the silicon surface during film deposition does not significantly affect the initial cell performance, but causes degradation of the devices under ultraviolet light. This is attributed to the generation of interface states during the plasma deposition process, accompanied by their simultaneous passivation with hydrogen. These "latent" states can be activated by UV light.
The nitride deposition by the reaction of SiH4 with NH3 or N2 were performed in three different glow discharge reactors: Two parallel plate reactors with frequencies of 450 kHz and 13.56 MHz, respectively, and a remote plasma reactor. Plasma damage and thus UV degradation of the cells could be avoided using a 13.56 MHz direct plasma or a remote plasma with NH3 as excited gas. Surprisingly, severe damage was observed by remote plasma nitride deposition with N2 as excited gas.