Influence of temperature during phosphorus emitter diffusion from a spray-on source in multicrystalline silicon solar cell processing

We have investigated the influence of diffusion temperature during phosphorus emitter diffusion from a spray-on source on the performance of screen-printed multi-crystalline silicon solar cells. Because of the dual diffusion mechanism present at high concentration in-diffusion of phosphorus in silicon, applying lower diffusion temperatures for a longer duration results in significantly enhanced penetration of the low concentration tail relative to the high concentration region. Moreover, we show that the sheet resistance of in-diffused emitters from a high concentration source depends primarily on the extension of the high concentration region, thus significantly different emitter profiles can be manufactured without altering the sheet resistance considerably. Because of the enhanced tail penetration, emitters Of a specified sheet resistance diffused at reduced temperatures can result in higher fill factors of screen-printed solar cells due to diminution of Schottky type shunts. Furthermore, emitters diffused at lower temperatures for longer durations can yield a higher gettering efficiency, resulting in increased bulk recombination lifetime, and thus a higher internal quantum efficiency at long wavelengths. The deeper tail extension of low temperature emitters, however, causes increased absorption within the highly recombinative emitter, resulting in current losses due to a lower internal quantum efficiency at short wavelengths. Copyright (c) 2006 John Wiley & Sons, Ltd.