A novel simultaneous boron and phosphorus diffusion technique is presented to produce simple, high-efficiency n(+)pp(+) 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 tired dose of P2O5 or B2O3 to the diffused sample. The resulting diffusion glass is extremely thin (similar to 60 Angstrom), which allows for the in situ growth of a passivating thermal oxide without increasing the solar cell reflectance. Reverse saturation current density (J(o)) measurements show that the in situ oxide passivation for a light boron and phosphorus diffusion provides excellent passivation properties, resulting in J(o) values in the 100 fA/cm(2) 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 (similar to 6 mu s) for the wafers on which the boron spin-on film was directly applied. This process was validated by fabricating in situ oxide passivated, n(+)pp(+) 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.