Preparation of highly textured surface ZnO thin films

In order to investigate the influence of the deposition technique upon the surface morphology of ZnO thin films we have employed two methods, which are the spray pyrolysis and magnetron sputtering. The surface morphology of ZnO thin films is a crucial parameter for controlling the reflection losses reduction when the coating is used as a transparent front layer in solar cells. The morphology of the surface was characterized by optical microscopy and profilometry. The results indicate that spray technique enables the elaboration of films with a highly rough surface, however sputtering technique yields to smoother films. This difference originates from the different deposition processes involved in both techniques. A vertical r.m.s. (root mean square) roughness in the order of 200 nm was measured in sprayed film; however only 40 nm r.m.s. vertical roughness is reported in sputtered one. The surface morphology in sprayed films causes the incident light diffraction; consequently the reflection is reduced up to zero. Therefore we show that ZnO thin films deposited with spray method is a potential candidate for use as a front transparent layer in solar cells.