Sol–gel derived ZnO thin films: Effect of amino-additives

Zinc oxide thin films were dip-coated from an alcoholic sol of zinc acetate with different amino-additives including monoethanolamine, diethanolamine, triethanolamine, triethylamine, and ethylenediamine. Sol–gel behavior, crystal structure, optoelectronic and morphological properties of thin films were investigated with focus on the effects of different amines and drying conditions. Investigations explicate the role of chemical and physical properties of amines such as organic chains, polarity, and boiling point as the main factors that cause distinct sol–gel behavior and film properties. It is shown that different amines in different molar ratios together with drying temperature cause dramatic impacts on sol transparency, stability, and consequently on structural, optoelectronic, and morphological properties of films. Notably, monoethanolamine and triethylamine films demonstrate a preferred orientation stimulated by increased molar ratio of amines. Further investigations indicated the positive effect of elevated drying temperature particularly on those films prepared from sols with high-boiling-point stabilizers. The variation of film optoelectronics seems to depend mainly on heat treatment, whereas sol chemistry influences the optical properties indirectly through the structural alteration. Peculiar morphologies in the ethylenediamine films disappeared with adjusting the drying conditions. The size of ZnO grains were approximately independent of amine types and primarily affected by the heat treatment