Microstructure And Properties Of CuInSe2 Thin Films Prepared By SILAR Method

The science and technology of solar cells as new energy resource free of pollution have undergone revolutionary evelopments since the discovery of Si photovoltaic device reported in 1954. The I-III-VI chalcopyrite materials have some very desirable properties, in which CuInSe2 with bandgap of 1.04 eV has proved to be a leading candidate for photovoltaic applications. This paper gives an overview of the progress in solar cells, preparation of the related thin films, and the properities of CuInSe2 thin films. The preparation of CuInSe2 thin films by Successive ions layer adsorption reaction (SILAR) method was researched.SILAR method is based on the immersion of substrates alternately in separate cationic and anionic precursor, and the film growth depends on the mechanism of heterogeneous growth. By now literature surveys show that there is little attempt to prepare CuInSe2 thin films by SILAR method. In this paper, the separate or mixed cation precuesor solution systems were firstly explored and the Cu and In mixed cation precursor with double chalating agents (TEA and CitNa) was selected to deposit CuInSe2 thin films. The influence of processing conditions, i.e. concentration of precursor solutions, adding of surfacants, water bath temperature, the numbers of cycle, annealing treatment on microstructure and properties of the CuInSe2 film were investigated according to analysis of TG-DTA, XRD, XPS, SEM and UV-VIS.The experimental results showed that Cu and In ions were well chalated with the double complexing agents in the mixed cation precursor solution, and the films derived from the mixed cation precursor solution had fewer impurities than that from the separated cation precursor solution. When water bath temperature was 70℃, uniform and compact film was achived with a growth rate of about 21nm/cycle, which indicated that the ions adsorpted to the substrate were of multi-layers. Chalcopyrite CuInSe2 thin film with near stoichiometry was obtained from Cu/In=1.5 in mixed cation precursor solution after annealed at above 380℃.in Ar atmosphere for 30 min. The annealing process was effective for crystallization and surface uniformity of the as-grown film. Morphology of the CuInSe2 thin films could be changed by adding surfactants into precursor solution. There were clusters on the surface when adding PEG20000, small size grains and homogenous surface when adding sodium dodecylbenzene sulfonate and nano-rods when adding hexadecyl trimethyl ammonium bromide. Absorption coefficients of these CuInSe2 thin films were all more thanl04cm-1: and the hightest value of more than 105cm-1 appeared in the microstructure consisted of nano-rods. Band gap of the CuInSe2 thin films were 0.92 ~ 0.96 eV.