Abstract
M.Sc.
Techniques for the fabrication of polycrystalline silicon solar cells have advanced in recent years
with efficiencies exceeding 17%. The major advantage of polycrystalline silicon is its low cost
relative to single-crystalline silicon. The disadvantage is the significantly smaller minoritycarrier
bulk diffusion length and inhomogeneous nature of the material. These two drawbacks
are due to the presence of grain boundaries as well as high concentrations of dislocations and
other physical and chemical defects. In this study the experimental conditions were determined
to fabricate solar cells on polycrystalline silicon substrates. The controlled diffusion of phosphorous
into silicon and subsequent evaluation of the doped layers (by spreading resistance profiling
and chemical staining) were important aspects of this study. From these results the diffusion
parameters (i.e. temperature and reaction times) could be optimized in order to improve the
solar cell output parameters. Additional material improvement (increase in surface- and bulk
minority carrier lifetimes) was demonstrated by the hydrogen passivation of electrically active
defects in polycrystalline silicon. However. measurements on hydrogenated silicon samples also
indicated that excess passivation can result in surface damage and subsequent reduction in the
minority carrier lifetimes. Preliminary solar cells were fabricated on polycrystalline silicon with
efficiencies ranging between 0.5 and 6% (total area = 16 cm2).