Copper indium diselenide films deposited by spray-pyrolysis

Cu_1-xIn_x Se₂ (0.45≤ x ≤0.80) films were deposited on glass substrate by spray pyrolysis technique, for use as absorbing layer of photovoltaic cells. The structural, morphological, optical and electrical properties of the films were analyzed according to the variation of the stoichiometry used. The analysis by X-ray diffraction showed that the most intense peaks were of orientation (204/220) and the films have the phases CuSe, CuSe₂ and CuInSe₂. The films showed uniform surface without cracks independently of the stoichiometry used. In the electrical characterization, the deposited films showed activation energy of the electrical conduction process with average value of 0.74 eV and typical behavior for semiconductors. The optical characterization was performed at the wavelength gap of 350 to 1100 nm, and the films showed absorption coefficient on the order of 10³ cm^-1 in the wavelength of 550 nm and optical band gap of 1.4 eV. The results indicated that the most suitable condition for deposition of films for their application as absorbing layer had as substrate temperature 400 °C, a solution flow rate of 1 mL/min, deposition time of 10 min and stoichiometry of Cu_0.2In_0.8Se₂, thus obtaining films without cracks, with large absorption coefficient of 6.8x10³ cm^-1 for the wavelength of 550 nm, thickness of approximately 2.5 μm and electrical resistivity of 0.13 kΩ.m at room temperature. (author)