High Efficiency Industrial p-type PERC and PERT Crystalline Silicon Solar Cells: Boron Junction Doping and Surface Passivation

As photovoltaic (PV) energy will gradually become one of the main renewable energy sources to replace conventional energy sources in the next decades, industry needs to pay attention to mass production of cost-efficient solar cells. At present, p-type crystalline silicon (c-Si) solar cell is the mainstream cell product in PV industry due to cost-efficiency. In p-type c-Si solar cells, industrial PERC (Passivated Emitter and Rear Cell) and PERT (Passivated Emitter and Rear Totally-diffused) cells are two potential candidates towards even higher cost-efficiency. To achive this, a systematic study is needed on both PERC and PERT cells from an industrial research perspective, which is the aim of this thesis. The first part of the thesis studies the industrial PERC cell. The key processes of Al2O3 passivation and screen-printing aluminium local back surface field, as well as integration of the entire PERC process are discussed, based on which a cost-efficient industrial PERC roadmap is presented. The loss mechanisms of cell efficiency and recombination are analyzed based on key characterizations combined with PC1D/PC2D simulations, and effective solutions are put forward to decrease these losses and thus to increase cell efficiency. The second part of the thesis presents a study on boron implanted junction, junction passivation and metal/p+-Si ohmic contact, as well as their application into the industrial p-PERT cells. Firstly, the focus is placed on the impact of junction profile and surface passivation on boron emitter quality, which can be influenced by implantation and anneal parameters. High-quality boron emitters passivated with in-situ grown SiO2 are obtained. Secondly, a novel junction passivation scheme using SiO2/Al2O3/SiNx is presented, which demonstrates effective passivation on both p+ and n+ emitters due to an excellent chemical passivation combined with a weak field-effect passivation. Then, an industrial roadmap for p-PERT is presented, which is based on fully ion implanted (boron and phosphorus) technology and the presented two junction passivation schemes. The cell results indicate that p-PERT cell using this roadmap is promising candidate for the PV industry. The final part of the thesis presents an outlook for a future roadmap extending the cell efficiency of industrial p-type c-Si solar cells towards and beyond 24%.