SiNTO EWT silicon solar cells
In this work we combine the SiNTO cell process with the EWT cell concept. All masking steps are performed by inkjet printing technology. The via-holes and laser-fired contacts are created by high-speed laser drilling. A new polishing process, which is suitable for inkjet masking, to pattern the interdigitated grid on the rear side is developed. For passivation purposes a thermal silicon oxide is used for the rear surface and a silicon nitride antireflection coating for the front surface. An e-gun evaporated aluminium/titanium/silver stack is used for the metallization, where the silver acts as a seed layer for a subsequent electro-plating step. Conversion efficiencies up to 16.9% on FZ material are obtained. The emitter is additionally analyzed on symmetric lifetime samples. Two different emitter diffusion processes, a 35 and a 65 ohm/sq. POCl3 diffusion process are regarded. An emitter diffused from a phosphorus doped silicon oxide layer in the same diffusion process as the 35 ohm/sq. emitter is analyzed as well. Emitter saturation current densities as low as 286 fA/cm2 are reached for an oxidized emitter.