Effects of Sb on the film formation of CuInSe2

Full text : Thin films of CuInSe2 (CIS) for high-efficiency photovoltaic application can be prepared by coevaporation or selenization. In this work, it is demonstrated that the addition of Sb to both film formation processes may result in highly compact grain structure and smooth surface. This film was prepared by co-evaporation with the addition of Sb during the film deposition process at a substrate temperature of 450 degrees Celsium. The Sbbeam flux was as high as that of Se, but only trace of Sb in the film was detected by SIMS. Electrical characterization indicated that the incorporation of Sb in the CIS lattice acted as an acceptor. We also prepared the CIS films using the rapid thermal selenization technique. A thin Sb layer with the thickness of 15 nm was inserted between Cu and In, which could prohibit the formation of Cu-In alloy during the precursor deposition processes. Namely, the precursor films with the Cu/Sb/In/Se stacking sequence were deposited on a soda-lime glass substrate. A suitable annealing condition could obtain a CIS film with large grain and smooth surface. Composition analysis using EPMA indicated that the CIS:Sb film prepared by rapid thermal selenization had a fairly uniform composition. Though the mechanisms of the film formation are different for the evaporated and selenized films, the effect of Sb seems to benefit the grain growth and leads to large grain and compact grain structure.