An investigation was made of the influence of diffusion temperature, during P emitter diffusion from a spray-on source, upon the performance of screen-printed multicrystalline Si solar cells. Because of the dual diffusion mechanism present at high-concentration in-diffusion of P in Si, applying lower diffusion temperatures for a longer time resulted in significantly enhanced penetration of the low concentration tail relative to the high concentration region. Moreover, it was shown that the sheet resistance of in-diffused emitters from a high concentration source depended mainly upon the extension of the high-concentration region. Thus, significantly different emitter profiles could be manufactured without significantly altering the sheet resistance. Because of the enhanced tail penetration, emitters of a specified sheet resistance diffused at reduced temperatures could result in higher fill-factors of screen-printed solar cells due to the diminution of Schottky-type shunts. Furthermore, emitters diffused at lower temperatures for longer durations could give a higher gettering efficiency; resulting in increased bulk recombination lifetime  and thus a higher internal quantum efficiency at long wavelengths. However, the deeper tail extension of low-temperature emitters caused increased absorption within the highly recombinative emitter, resulting in current losses due to a lower internal quantum efficiency at short wavelengths.

Influence of Temperature during Phosphorus Emitter Diffusion from a Spray-On Source in Multicrystalline Silicon Solar Cell Processing. A.Bentzen, G.Schubert, J.S.Christensen, B.G.Svensson, A.Holt: Progress in Photovoltaics, 2006, 15[4], 281-9