Controlled Texture of Magnetron Sputtered Transparent Conducting ZnO: Al Films for Solar Cell Applications

Abstract

Textured transparent and conducting ZnO:Al films were prepared by rf-magnetron sputtering on glass substrate at a temperature 3500C under Ar and Ar+O2 gas ambient. ZnO:Al thin films shows a minimum electrical resistivity of (~8.210-4 Ω-cm), and high optical transmittance (T~86–90% average) in visible region. With increasing of oxygen concentration ZnO:Al films become more compact, stoichiometric and becomes more electrically resistive. ZnO:Al shows hexagonal wurtzite polycrystalline structure with strong (002) orientations. The grain size of ZnO:Al film is 26 nm . Granular structure is observed in 2d–view of AFM image. The RMS value (δrms) of surface roughness of Ar deposited ZnO:Al and Ar+O2 deposited ZnO:Al films are respectively 6.13nm and 13.56nm. The above surface roughness value is under the critical δrms value (38nm) of the TCO surface to achieve best photovoltaic performance in thin film solar cell. O2 plays an important role in controlling surface morphology, surface texture as well as the internal texture of the growing film. There is special correlation between materials properties (opto-electronic, electrical, structural as well as morphological) and film growth condition, finally tuning the surface texture and structural properties has been enlightened in terms of a Modified Thornton Model Keywords: ZnO: Al films, Magnetron Sputtering, Surface Texture, Modified Thornton model, Atomic Force Micrograph.