Enhancing Precursor Quality of Cu-In-S Ternary Thin Films by Applying More Appropriate Deposition Procedure

Abstract

Copper indium sulphur (CIS) thin films were electrochemically grown from an acidic aqueous solution including 10 mM CuCl2, 10 mM InCl3, 20 mM Na2S2O3 and 200 mM LiCl. Deposition potential is determined by means of cyclic voltammetry analysis. The precursor CIS thin films are produced at -1.10 V for 600 s, -0.90 V for 300 s and a mixed potential of -0.25 V for 150 s and -1.10 V for 150 s. It is reported that surface morphology and film stoichiometry vary remarkably with the deposition parameters. SEM images show a variation in the grain shape, homogeneity and agglomeration due to the different Cu/In ratio. The produced films have XRD peaks belonging to both CIS2 crystalline phase and S element. The produced CIS material at -1.1 V has a band gap of 1.66 eV. The CIS thin film produced at -0.9 V has three different band gaps such as 1.76, 2.59 and 2.85 eV. The CIS material produced by two steps has also three different band gaps between 1.59 and 2.74 eV. The CIS films are p-type, and resistivity and mobility data are in the range 6.56-8.61 Ωcm and 8.68-22.2 cm2/Vs, respectively. It is found that the acceptor concentration of CIS thin films varies between 2.48x1017 and 1.06x1018 cm-3. In summary, this study reports a procedure to produce high-quality precursor CIS thin films, highlighting a promising material to be used in heterostructure photovoltaic devices as a p-type absorber layer.