Plasma immersion ion implantation (PIII): New path for optimizing doping profiles of advanced phosphorus emitters

Session 6: Process Integration and Low-cost ManufacturingInternational audienceA key step to achieve high conversion efficiencies for silicon solar cells is the junction formation. Plasma Immersion Ion Implantation (PIII) enables fine variations of the surface dopant concentration and depth of the doping profiles. Since no “dead-layer” with electrically inactive dopant species remains after an activation annealing step, high electrical quality of doped regions can easily be performed. We studied whether advanced Phosphorus emitters obtained via PIII could be optimized to increase p-type crystalline silicon (c-Si) solar cell performances. The doping profiles were tuned by changing ion dose and post implantation activation annealing temperature (Tanneal). A detailed analysis of carrier recombination in the different part of Al-BSF solar cells has been performed. Thus, saturation current densities (J0) were extracted (passivated emitter J0e,passivation, metallized emitter J0e,metallization, c-Si bulk and Back Surface Field J0,bulk+BSF) by coupling IC-QssPC and Suns-Voc measurements on specific test structures. An increase in Voc and Jsc was obtained by lowering the ion dose for a given Tanneal, whereas Voc, Jsc and the Fill Factor (FF) were improved by lowering Tanneal for a given dose. In the first case, photovoltaic (PV) conversion efficiencies did not change because of an increase in series resistance. However in the second case, they were increased by 0.2% absolute by reducing Tanneal from 850°C to 800°C, with a high FF value of 79.3% despite a relatively high emitter sheet resistance (115 Ω/square)