The bulk lifetime $\tau _{n}$ and diffusion length
Ln of minority carriers vary through the height of a cast
multicrystalline silicon (mc-Si) block. This variation is due to the
segregation of metallic impurities during the directional solidification and
the native impurity concentrations increase from the bottom to the top of
the ingot, which is solidified last, while the ingot bottom, which is
solidified first, is contaminated by the contact with the crucible floor. It
is of interest to verify if a correlation exists between the bulk lifetime
$\tau $ of as cut wafers and the conversion efficiency $\eta $ of solar
cells. In a very large ingot (>310 kg), it was found that $\tau_{0}$, in raw wafers, $\tau_{dif}$ in phosphorus diffused
ones and Ln in diffused wafers are smaller in the top and in the bottom
of the ingot. The same evolution is observed in solar cells, however the
diffusion length values Lcel in the central part of the ingot are
markedly higher than those found in diffused wafers, due to the in-diffusion
of hydrogen from the SiN-H antireflection coating layer. The variations of
$\eta $ and those of $\tau _{0}$, along the ingot height, are well
correlated, suggesting that the evaluation of $\tau _{0}$ can predict the
properties of the devices. In addition, segregation phenomena around the
grain boundaries are observed at the bottom of the ingots, due to a marked
contamination by the crucible floor, and at its top where impurities are
accumulated. These phenomena are linked to the long duration of the
solidification process and the large amount of imperfect silicon used to
cast the ingot.