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Influence of the boron emitter profile on VOC and JSC losses in fully ion implanted n-type PERT solar cells



In this work, we report on fully ion implanted 156 × 156 mm2 n-type PERT solar cells fabricated in an industry-capable process. The implant damage of phosphorous and boron was co-annealed in a single furnace annealing step. The cells feature a screen-printed front side metallization and an evaporated rear side metallization. The influence of boron emitter profile on the open-circuit voltage VOC and the short-circuit current density JSC was studied by comparing two boron doses (2.5 × 1015 cm−2, 3 × 1015 cm−2) and two annealing durations (20 min, 80 min). The solar cells reach tightly distributed efficiencies above 20% (20.3% maximum). Cells featuring an emitter implanted with 2.5 × 1015 cm−2 boron dose annealed for 80 min show the highest open-circuit voltages up to 668 mV. As compared to implied open-circuit voltages measured on non-metallized cell precursors, this corresponds to a metallization-induced voltage loss of 14 mV. For the shorter annealing time (corresponding to a shallower profile) but same boron dose, the VOC loss is 18 mV. The fact that the cells with the higher boron dose of 3 × 1015 cm−2 showed lower VOC values indicates that the recombination at the Ag/Al-p+ Si contacts is not totally dominating. We determine the recombination current densities of the metallized emitter regions to 900–1900 fA cm−2. Contrary to the dependence of VOC on the emitter profile, JSC is lower for deeper emitters. The loss in JSC is visible in the internal quantum efficiencies IQE at short wavelengths. Strategies for an optimization of both quantities, JSC and VOC, are discussed.

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