Fabrication of textured solar cells using sprayed phosphoric acid as the dopant source for the in-line emitter diffusion

Solar cells were fabricated from textured boron-doped Cz-Si 125Ã 125 mm2 pseudo-square wafers with a bulk resistivity of 0.5-1.7 ohm cm or 3-6 ohm cm. The emitter was formed by spraying a solution consisting of 3% w/w phosphoric acid in DI water and of a small quantity of surfactant onto the wafer and by subsequent diffusion at 880°C in a contamination-free in-line furnace. The contacts were formed using standard screen-printing and in-line fast firing. Sheet resistance Rsh was in the range of 38-43 ohm/sq and the cells yielded efficiencies of up to 17.5%. Fill factors of up to 79.1% indicate adequate emitter homogeneity on a microscopic scale. Some factors influencing Rsh homogeneity across a wafer were dentified, such as the movement of the drying front of the sprayed layer. A Rsh variation of approx. ±3 ohm/sq was measured on 125x125 mm2 pseudo-square wafers with an avg. Rsh of ~50 ohm/sq.