Preparation Of CuInS₂ Photovoltaic Thin Films By Single Sourcevacuum Co-Evaporation

Single source vacuum co-evaporation was utilized to prepare CuInS2 thin films. The heat-treatment was conducted in N2 environment. The effects of Cu-In-S mixed ratios and heat-treatment conditions on properties of thin films were studied. The crystalline structure, surface morphology and roughness, chemical composition, film thickness, optical and electronic properties of thin films were characterized by X-ray diffraction, atomic force microscope, scanning electron microscopy with energy dispersive analysis, X-ray photoelectron spectrum, manual profiler, ultraviolet-visible spectrophotometer, four-probe meter, respectively.Experimental results show that appropriate S atomic ratio, defined as X, is an important factor. In this paper, X value was chosen in range from 0.2 to 2 and the optimal ratio of Cu-In-S is 1:0.1:1.2. The CuInS2 thin films, which were deposited under the optimal ratio, showed chalcopyrite crystalline structural. The thin films with non-annealing present deficiency in crystallization and have Cu1.7In0.05S mixed phase. The microstructure of CuInS2 thin films could be improved obviously and could get [112] preferred orientation if the heat treatment condition was controlled in N2 for 20 mins at 400℃. The morphology of the thin films were compact and homogeneous. The average grain size, thickness and surface arithmetic average roughness were 38.06nm,454.8nm and 13nm, respectively. Stoichiometries of surface and body's elements in thin film were 1:2.4:1, 1:0.9:1.5, which deviated 3.2% and 0.8% to standard stoichiometry. The absorption coefficient is 105 cm-1 and the optical bandgap is 1.42 eV. The conductor type and resistance of thin film were P-type and 4.8×10-2Ω·cm.The crystalline structure of thin film kept unchanged when heat-treatment temperature raise to 440℃for 10 mins. Stoichiometries of surface and bulk elements increased and deviated 8.8%,3.3% to standard stoichiometry, which were 1:6.2:0.6 and 1:2.3:0.8. The presence of gap In in crystal lattice resulted in the conductor type shifting to N-type. Optical absorption coefficient of thin film decreased to 104cm-1; optical bandgap became narrow which was 1.39eV; and the resistance of thin film was 1.3×10-2Ω·cm.