Study of ZnO:Al films for silicon thin film solar cells

In this study, aluminum doped zinc oxide (ZnO:Al) films deposited from dual rotatable ceramic targets are systematically investigated. The influences of substrate temperature and working pressure as well as discharge power on different properties of ZnO:Al films including deposition rate, surface structure, optical and electrical properties as well as etching behaviors are studied. It is found that in addition to substrate temperature and working pressure the discharge power plays an important role in material properties of ZnO:Al films. Low rate ZnO:Al (LR-AZO) films with high carrier mobility of about 50 Vs/cm2 and high rate ZnO:Al (HR-AZO) films of more than 90 nm m/min with high carrier mobility of about 45 Vs/cm2 are achieved. However, there is only a narrow parameter window to achieve a regulated crater-shape surface structure for ZnO:Al films after a chemical wet etching process. The surface-textured ZnO:Al films were applied in silicon thin film solar cells and high efficiencies of 8.5% and 11.3% are achieved for single junction hydrogenated microcrystalline silicon (μc-Si:H) solar cells and amorphous/microcrystalline silicon (a-Si:H/μc-Si:H) tandem solar cell, respectively.