Surface passivation for solar cells by large scale inline sputtering of silicon nitride

In this work we present first results of silicon nitride (SiN:H) surface passivation layers produced on a prototype of the ATON series - a large area inline sputtering system. Corresponding to the application on the front ore the backside of solar cells we carried out experiments on lowly doped emitters, on p-type 1-2 ohm cm floatzone (FZ) material and on the back side of silicon solar cells. When deposited on both sides of FZ wafers with lowly doped emitters equal lifetimes for PECVD and sputtering were measured. According to this equal cell efficiencies on Cz solar cells with lowly doped emitter have been observed. The results on p-type FZ material reveal a strong dependency of the lifetime on the sputter power, the substrate temperature, the process pressure and the hydrogen content of the SiN:H. The best processes lead to carrier lifetimes about 370 µs - at an injection level of 1*1015 /cm3 - which is equivalent to a surface recombination velocity of 30 cm/s. When applied to a cell concept with LFC back side sputtered SiN:H nearly reached the same level in cell performance as cells with PECVD SiN: