Fabrication and analysis of high-efficiency polycrystalline silicon solar cells

Phosphorus and aluminum gettering conditions were optimized to achieve high-frequency polycrystalline silicon cells. In order to take advantage of intense gettering without the harmful effects of the emitter dead layer, a deep phosphorus diffusion at 930°C was performed, followed by a partial etch-back of the n⁺ region. The optimum aluminum treatment for these cells included 1.2-μm-thick Al deposition followed by 850°C, 35-min drive-in. Oxide passivation was found to be effective in cells made on these polysilicon wafers. A combination of optimum phosphorus and aluminum getting, oxide passivation, and double-layer antireflection coating resulted in record 17.7% efficient, 1-cm², cells under one sun illumination. Cell model calculations were performed ignoring the grain boundary effects, but using a measured effective lifetime in the cell. A good correlation was found between measured and calculated cell parameters of the 17.7% efficient polycrystalline silicon cell. Model calculations were extended to outline an approach toward achieving greater than 20% efficient cells