Characterization of copper indium sulfide absorber films deposited by ultrasonic spray pyrolysis technique for photovoltaic applications

CuInS2 thin films are one of the I-III-VI2 chalcopyrite-type mixed crystal semiconductor having direct band gap around 1.5 eV and high absorption coefficient. Hence, it is possible to produce highly efficient thin film solar cells from CuInS2 as the absorber layer. In this thesis, CuInS2 thin films have been deposited using spray pyrolysis system equipped with ultrasonic impact nozzle. With this technology, precursor solution is ultrasonically excited using piezoelectric crystals to generate very fine droplets. This allows deposition of homogenous and defect free films. Here, effects of system parameters, such as solution amount, stoichiometry, substrate temperature, infuse rate and solvent type on the film properties have been investigated. Structural properties of the CulnS2 thin films were examined through X-ray Diffraction, Energy Dispersive X-ray Analysis and X-Ray Photoelectron Spectroscopy. For the optical characterization of CuInS2 films, the transmission measurements have been carried via UV-VIS-NIR spectroscopy. Electrical resistivity and the photosensitivity of the films have been determined from room temperature I-V measurements. Moreover, temperature dependent electrical conductivity have been performed to investigate the carrier concentrations and the mobility CuInS2 films. Structural characterization of CuInS2 films revealed that both increasing the Cu concentration in precursor and the substrate temperature improved the crystallinity of the films. Low infuse rate values and alcoholic solutions allowed to deposit very homogeneous and agglomerate free films. According to optical transmission data all sprayed films showed high absorption coefficient and desired optical band gap values, which is required for high efficiency absorbers.