Effect of growth period on optical properties of CBD grown nano-scale ZnO thin films for application in CIGS solar cell

In the present study, ZnO thin films were deposited for different deposition time periods using chemical bath deposition technique on a seeded substrate at a selected pH value and concentration based on the earlier findings. In order to optimize the deposited thin film to be used as buffer layer in thin film CIGS solar cell, optical characterization was done by using UV/VIS spectro-photometry and various parameters like transmittance, reflectance, refractive index, absorption coefficients, dielectric constant, optical conductivity etc. were calculated. The highest transmittance of 92.9% was recorded for the sample with deposition time 1 hour, which further decreased to 90.8% for deposition time of 1.5 hour and then fell down to 87% for a growth period of 2 hours. A blue shift as compared to the bulk was observed in the band gaps of all the three samples. Absorbance, reflectance, absorption coefficients, refractive indices and optical conductivities were found to increase with deposition time. The study laid a foundation stone for understanding the use of as deposited ZnO nano-crystalline thin films in thin film CIGS solar cell by correlating the growth period at a optimized pH and concentration with its various optical parameters.