Mass production and modeling of high efficiency n-PERT solar cells with ion implanted BSF/selective-BSF

Ion implantation is a technique which has already been successfully transferred from integrated circuits (IC) industry to photovoltaic (PV) industry, especially for p-type solar cells fabrication. Based on the configuration of Yingli n-PERT PANDA cells, phosphorus implantation is employed to fabricate n+ back surface field (BSF) as an alternative to POCl3 diffusion. A 20.3% cell efficiency on average with a maximum value of 20.5% was achieved in mass production by process optimization such as ion implantation, annealing during PECVD and passivation improvement. Resulted modeling data indicates that the selective-BSF (SBSF) cell efficiency gain was 0.2% absolute compared with rear totally homogeneous doped cell after process optimization and the SBSF cells reach the best efficiency at a wafer resistivity around 0.5-1 Ω cm depending on wafer lifetime. In this work we proved that cells with efficiency higher than 21% can be realized by optimizing sheet resistance of rear surface and improving passivation.