Surfactant-mediated growth of nanostructured zinc oxide thin films via electrodeposition and their photoelectrochemical performance

Zinc oxide (ZnO) thin films were electrodeposited from an aqueous zinc acetate solution onto fluorine-doped thin oxide (FTO) coated conducting glass substrates. The effect of organic surfactants like polyvinyl pyrrolidone (PVP), sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), ethylene glycol (EG) and polyvinyl alcohol (PVA) on their structural, morphological, optical and photoelectrochemical properties was studied. The x-ray diffraction patterns revealed the formation of phase-pure ZnO thin films. The films deposited using organic surfactants exhibit different surface morphologies. It was observed that the organic surfactants play important roles in modifying the surface morphology and size of the crystallites. A compact granular morphology was observed for the ZnO samples grown without organic surfactants. The films exhibit nanoparticles of size 100-150 nm for PVP, EG and PVA mediated growth. The vertically aligned thin and compact hexagonal crystallites stem from the SDS, whereas microporous corrugated morphology is observed for PEG-mediated growth. All the samples exhibit room temperature photoluminescence (PL). Oxygen vacancies contribute to the active luminescent centers for the emission of green light in ZnO thin films. PL gets quenched for the SDS surfactant. All the samples were post-treated with ethanol to remove stray surfactant molecules. FTIR study was used to confirm the removal of adsorbed surfactant molecules from the samples. Moreover the samples are photoelectrochemically (PEC) active and exhibit the highest photocurrent of 231 νA, a photovoltage of 492 mV and 0.42 fill factor for the ZnO:SDS films.