Study on the role of growth time on structural, morphological and optical properties of un-capped and L-cyst.-capped ZnO nanorods grown on a GZO seeded thin film layer from an aqueous solution

Abstract

The influence of the deposition time (ranging from 30 to 300 min) and the role of l-cysteine on the structural and optical properties of the un-capped and L-cyst.-capped ZnO nanorods (ZNRs) grown using the chemical bath deposition method was discussed. X-ray diffraction patterns showed that the estimated crystallite size increased with the deposition time up to 240 min for both capped and un-capped samples, while the calculated strain was found to decrease to a minimum for the 240 min deposition time. The Fourier transform infra-red spectroscopy of the as-grown ZNRs films showed various absorption bands in the range of 250–4000 cm-1 indicating the presence of different functional groups. Scanning electron microscopy analysis illustrated that the aspect ratios of the L-cyst.-capped ZNRs increased six-fold as the growth duration varied from 30 to 240 min, but decreased slightly at longer growth time. The root mean square roughness increased continuously from 10.9 to 36.3 nm as the growth time was raised from 30 to 240 min for the un-capped ZNRs. The samples deposited at 240 min exhibited the highest photoluminescence emission intensity ratios suggesting a low density of deep level defects. An inverse relation between the optical band gaps and growth time was observed. The highly luminescent cyst.-capped sample, with well-aligned nanorods and highest aspect ratio and good crystallization grown at 240 min growth time can be used as a possible photoanode component of dye-sensitized solar cells.