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Abstract:
Due to its attractive optical, electrical, and chemical properties, the
ternary CuInSe2 (CIS) chalcopyrite-type semiconductor is widely employed
as an absorber layer in thin-film photovoltaic devices. Experimental
studies have shown that close to the interface of CIS with the CdS
buffer layer the former is Cu-depleted, corresponding most probably to
an ordered vacancy compound (OVC), and hosts some Cd atoms by diffusion,
which originate from the buffer layer. To gain new insights into the
insertion of Cd into Cu-depleted CIS phases, we have performed density
functional theory calculations, and we have investigated the atomic
structure and energetics of neutral Cd impurities in the OVC CuIn5Se8.
We found that Cd atoms prefer predominantly to sit on Cu sites or on Cu
vacancy sites. Furthermore, our calculations show that the Cu vacancies
and Cd atoms have high binding energy at least in some specific
configurations. Hence, the insertion of Cd into the CIS materials might
enhance the formation of Cu-poor phases.
