Emitter recombination current densities of boron emitters with silver/aluminum pastes

In this work, we investigate the recombination current density of ion-implanted boron emitters, which are contacted with a screen printed silver/aluminum paste. Depending on the peak doping concentration and on the depth of the doping profile, we measure a significantly increased recombination current density below those contacts of up to 3500 fA/cm². This is 3.8 times higher than the expectations obtained from device simulations. The metallized emitter surface recombination is lower when using an emitter with higher front side doping or deeper emitter doping profile. We present two approaches to reduce the recombination losses due to the metallization: (a) dual print with a non-firing busbar paste and fineline fingers yields a gain in efficiency of 0.4 % and (b) selective emitters with a higher emitter doping level underneath the front contacts and a lower doping in the intra-finger regions yield a gain in short-circuit current and open-circuit voltage compared to homogeneous emitters.