Evaluation of implantation annealing for highly-doped selective boron emitters suitable for screen-printed contacts

Ion implantation is a technology suitable for the formation of high quality junctions in silicon solar cell processing. As screen-printing is the state of the art metallization technique for industrial solar cells, the compatibility of ion implanted boron emitters with this metallization technique will be investigated. The fact that selective emitter structures can be in situ formed allows a high freedom in the design of the final emitter structure to meet the different demands of the metallized and passivated part of the emitter. In this work we investigate high dose implantations for the metallized area and low dose implantations for the passivated area that subsequently receive a short furnace anneal at 950 or 1050 °C. Applying a high dose in the range of 3e15 cm−2 high surface concentrations of around 6e19 cm−3 can be reached, allowing for a good contact of the screen-printed metallization. The passivated part of the emitter can be realized by implanting a lower dose (<1e15 cm−2). The sheet resistance is in the range of 110-160 Ω/sq resulting in very low emitter saturation current densities between 10 and 40 fA/cm2. Those experimental results demonstrate that ion implantation of selective boron emitters is compatible with industrial screen-printing technology and enables high cell efficiencies.