Passivation of boron emitters by local overcompensation with phosphorus
A novel approach for the passivation of boron emitters is presented. As it is more difficult to achieve low surface recombination velocities on highly doped p-type silicon (e.g. boron emitter) than on highly doped n-type silicon (e.g. phosphorus emitter) our approach is to locally overcompensate the surface of the boron emitter by a shallow phosphorus diffusion. This inversion of the surface doping from p-type to n-type allows the use of standard technologies which are used for passivation of highly doped n-type surfaces. A low emitter saturation current density (J0e) of 49 fA/cm2 on SiO2 passivated lifetime samples has been reached. On solar cells we achieved with this this n- EPF (Emitter Passivated by a Floating junction) cell structure a confirmed conversion efficiency of 21.7 % and an open-circuit voltage (Voc) of 676 mV.