20.5% efficiency on large area N-type PERT cells by ion implantation

4th International Conference on Silicon Photovoltaics, SiliconPV 2014International audienceWe developed a high efficiency N-type PERT (Passivated Rear Totally Diffused) bifacial structure based on B and P ionimplantation doping, SiO2 passivation and conventional screen-printing metallization. Two process flows were compared: a “coanneal” process and a process using separated anneals for B and P activation. We highlight the impact of the variations of the Bemitter and P- BSF profiles on the solar cells performance. The impact of the boron implantation dose was studied allowing tooptimize this parameter. Concerning the BSF, two temperature ranges were studied for the P activation leading to very differentBSF profiles. A shallower profile enables to reach high implied Voc while keeping low contact resistivity. The overalloptimization was integrated into a simplified and industrial process flow on large area Cz-Si solar cells (239cm²). An averageefficiency of 19.7% was reached using the “co-annealing” process. The efficiency in this case was limited by a low PFF. Thislimitation was solved using the “separated anneal” process where an average efficiency of 20.2% was obtained on a 15 cellsbatch with a 20.5% champion cell