Novel texturing method for sputtered zinc oxide films prepared at high deposition rate from ceramic tube targets

Abstract

Sputtered and wet-chemically texture etched zinc oxide (ZnO) films on glass substrates are regularly applied as transparent front contact in silicon based thin film solar cells. In this study, chemical wet etching in diluted hydrofluoric acid (HF) and subsequently in diluted hydrochloric acid (HCl) on aluminum doped zinc oxide (ZnO:Al) films deposited by magnetron sputtering from ceramic tube targets at high discharge power (∼10 kW/m target length) is investigated. Films with thickness of around 800 nm were etched in diluted HCl acid and HF acid to achieve rough surface textures. It is found that the etching of the films in both etchants leads to different surface textures. A two steps etching process, which is especially favorable for films prepared at high deposition rate, was systematically studied. By etching first in diluted hydrofluoric acid (HF) and subsequently in diluted hydrochloric acid (HCl) these films are furnished with a surface texture which is characterized by craters with typical diameter of around 500-1000 nm. The resulting surface structure is comparable to etched films sputtered at low deposition rate, which had been demonstrated to be able to achieve high efficiencies in silicon thin film solar cells.