The effect of solvent on the functional properties of zinc oxide films via AACVD

Abstract

Zinc oxide films were successfully synthesised from zinc acetate dihydrate in a dual-solvent mixture via aerosol assisted chemical vapour deposition (AACVD). Preferential growth in the (002) and (100) crystal planes was achieved through variation in the dielectric constants of the solvents. It was found that the solutions with greater dielectric constants increased the growth in the (002) direction, whilst toluene, which has a low dielectric constant, increased growth in the (100) plane. This leads to the ability to grow functional zinc oxide films with specific morphologies for a range of PV devices to optimise electron transport. Excellent conductivities of ∼6 and 1.3 S cm⁻¹ were obtained for undoped zinc oxide, using acetonitrile and toluene as the secondary solvents respectively, demonstrating that the morphology has little influence on Hall effect measurements. All films were transparent, where some met industry standards, reaching over 80% transmittance to visible light. Highly crystalline films have been produced, with low FWHM confirmed by XRD analysis, making these films suitable for doping to enhance their functionalities as electron transport layers. Water contact angle measurements confirmed the presence of both hydrophobic and hydrophilic zinc oxide films. The origin of the differing surface wettability was attributed to varying amounts of surface hydroxyl terminations, as determined by XPS analysis, demonstrating that the choice of solvent in the AACVD process can modify the ZnO surface chemistry and optimise for antisoiling purposes.