Selective emitter formation with a single screen-printed p-doped paste deposition using out-diffusion in an RTP-step

We present a new way to realise a selective emitter structure using a single screen-printed phosphorous paste deposition as dopant source to obtain a doping differential, with rapid thermal diffusion. The heavily doped part of the emitter is situated underneath the deposited phosphorous lines, and the lightly doped emitter in between is obtained via the gas phase, because phosphorous out-diffuses from the paste during the high-temperature step. SIMS profiles show a difference of a factor 4 in magnitude for the surface concentration between the regions underneath and beside the deposited paste. Photovoltaic results show an improvement in efficiency of 0.7% in comparison with the reference cell (homogeneous emitter), due to a 2 mA/cm2 short-circuit current increase.