Preparation and characterization of cost effective spray pyrolyzed absorber layer for thin film solar cells

• Cost effective spray deposition of CuInS2 absorber layer was reported.
• The lowest solution consumption in literature to form spray pyrolyzed thin films.
• Effect of solution loading on the physical properties of CuInS2 absorber layer.
• Temperature dependant electrical conductivity of the CuInS2 films was studied.
• Electrical conduction mechanism of the spray pyrolyzed CuInS2 was investigated.

In this study, highly (1 1 2) oriented crystalline copper indium disulfide (CuInS2) thin films with high mobility have been deposited via ultrasonic spray pyrolysis. Structural and electrical properties of CuInS2 thin films were examined to utilize them in solar cell applications. Various amounts of precursor solution ranging from 0.25 to 2.02 ml/cm2 were used to form CuInS2 thin films onto the soda lime glass substrates. Scanning electron microscopy (SEM) analysis revealed that all sprayed films were pin-hole and crack free. Atomic percent ratios of the Cu/In and S/In were very close to the targeted stoichiometric ratios of 1/1 and 2/1, respectively. X-ray diffraction (XRD) studies revealed that all the deposited films were polycrystalline and exhibiting the chalcopyrite structure. Optical band gap energy of the films were calculated as 2.85 eV and decreased to 1.40 eV by increasing the solution loading. Hopping mechanism could be considered as the dominant conduction mechanism in the studied temperature range. Carrier concentrations in CuInS2 films were ranging between 1015 and 1017 cm−3. Mobility and the carrier concentration of the CuInS2 thin films deposited from 1.52 ml/cm2 solution loading were 40.1 cm2/V s and 1.69 × 1017, respectively. At last but not least, the amount of solution used in this study to form CuInS2 thin films was one of the lowest values reported in the literature.