We have investigated the diffusion of phosphorous (P) in multicrystalline Silicon (Si) during solar cell emitter formation by secondary ion mass spectrometry (SIMS). From the experimental results, we observe significantly increased in-grain diffusion depths in areas of structural disorder that are not readily observed by the naked eye. We believe that this effect is due to increased concentrations of Si self-interstitials in the areas surrounding the defects, causing an enhanced transient response of elemental P diffusion. In areas adjacent to a grain boundary a slight, but notably smaller, enhancement of the P diffusion depth is observed. (c) 2006 Elsevier B.V. All rights reserved.