  We considered modification of the defect density of states in CdTe as
influenced by a buffer layer in ZnO(ZnS, SnSe)/CdS/CdTe solar cells. Compared
to the solar cells employing ZnO buffer layers, implementation of ZnSe and ZnS
resulted in the lower net ionized acceptor concentration and the energy shift
of the dominant deep trap levels to the midgap of CdTe. The results clearly
indicated that the same defect was responsible for the inefficient doping and
the formation of recombination centers in CdTe. This observation can be
explained taking into account the effect of strain on the electronic properties
of the grain boundary interface states in polycrystalline CdTe. In the
conditions of strain, interaction of chlorine with the grain boundary point
defects can be altered.
