A Novel Processing Technology for High‐Efficiency Silicon Solar Cells

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A novel simultaneous boron and phosphorus diffusion technique is presented to produce simple, high‐efficiency silicon solar cells in one thermal cycle. This technique uses boron and phosphorus spin‐on dopant films to fabricate limited solid doping sources out of dummy silicon wafers. This approach results in the delivery of a fixed dose of or to the diffused sample. The resulting diffusion glass is extremely thin (∼60 Å), which allows for the in situ growth of a passivating thermal oxide without increasing the solar cell reflectance. Reverse saturation current density measurements show that the in situ oxide passivation for a light boron and phosphorus diffusion provides excellent passivation properties, resulting in values in the range. Measurements of the bulk minority carrier lifetime show that by fabricating separate boron solid sources, trace impurities in the spin‐on dopant film are not transported to the diffused sample. This filtering action is shown to result in bulk lifetimes in excess of 1 ms for silicon doped indirectly from the source wafers but gives much lower lifetimes (∼6 μs) for the wafers on which the boron spin‐on film was directly applied. This process was validated by fabricating in situ oxide passivated, solar cells in one high‐temperature cycle incorporating several high‐efficiency features including surface texturing and a back side reflector, resulting in confirmed efficiencies in the 19–20% range. © 1999 The Electrochemical Society. All rights reserved.