Zinc Oxide Thin Film Morphology as Function of Substrate Position During Sputtering Process

Abstract

Transparent conductive oxides are materials combining great transparency with high conductivity. In photovoltaic applications, they are developed under thin layer for the realization of upper electrodes of solar cells. Among transparent oxide materials, Zinc Oxide (ZnO) presents unique properties, starting with its first qualities to be abundant, low-cost and non-toxic oxide. Zinc Oxide thin film was deposited on rectangular glass substrate by magnetron sputtering. After an overview of the properties expected for good transparent conductive materials, the effect of distance from the center of the cell on the morphology of the film was investigated by Atomic Force Microscopy (AFM). The scanning was done on different area of the sample as function of the distance from the central position of the direct sputtering jet. As far as the distance increased, it has been noticed a quasi-linear increase in thickness of the ZnO deposited film and a change in the grain shape from spherical to pyramidal with an increase in the size of the particles. Controlling the sputtering distance allows the control of texture, thus of the Haze factor, the photo-generation of excitons, as well the optical transmission of the TCO layer and finally an improvement in the efficiency of the so-built photovoltaic cells.