Structural and Optical Characterization of As-grown and Annealed ZnxCd1-xS Thin-films by CBD for Solar Cell Applications

Abstract

We report the synthesis of Zn x Cd 1-x S (x=0 to 0.41) thin-films on soda-lime glass substrates by chemical bath deposition technique and the as-grown Zn 31 Cd 0.59 S films are annealed at 200 o C, 350 o C, and 500 o C in the N 2 ambient for 20 minutes. The structural properties, optical properties, surface morphology and elemental composition of the films are characterized by XRD, UV-Vis N.I.R. spectroscopy, EDX., and FESEM. The thickness of the as-grown films is measured by the DEKTAK stylus profilometer and is in the range of ⁓100 nm-120 nm. The as-grown films show quasi-crystalline nature with preferential orientation along (002) hexagonal plane and the crystallinity is declined with the increment of zinc content. Also, the FESEM micrographs show the homogeneous growth, pinhole-free surface, and compactness of the films. The transmission edge is shifted towards the short wavelength region as the relative zinc content in the as-grown films increases, which confirms the significant reduction of photon absorption in the blue region of the solar spectrum. The as-grown films show average transmittance of ⁓80-90% along with a tunable bandgap of 2.50eV to 3.35eV for the variation of relative zinc content from 0 to 0.41. The annealing treatment improves the crystalline properties of Zn 31 Cd 0.69 S film and the best crystallinity is obtained at 350 o C temperature. Meanwhile, the annealed Zn 31 Cd 0.69 S films also exhibit a variable bandgap of 2.85eV, 3.10eV and, 3.22eV at 200 o C, 350 o C, and 500 o C respectively whereas the bandgap of the as-grown film is 3.12eV. Annealed Zn 31 Cd 0.69 S thin-film at 350 o C having enhanced structural properties without affecting optical characteristics and therefore it can be suitable as a good alternative buffer layer for thin-film solar cell applications.