Preparation of highly conducting Al-doped ZnO target by vacuum heat-treatment for thin film solar cell applications

Abstract

In thin film solar cell technologies, room temperature deposition of highly conductive Al-doped ZnO thin films as transparent conductive oxide is one of the most important factors that prevents the distortion of the bottom layers. In this work, we prepared Al-doped ZnO targets at different heat-treatment pressures including 103 mbar (air), 10−2 mbar (low-vacuum) and 10−5 mbar (high-vacuum). The results indicated that by performing the heat-treatment in vacuum under a pressure of 10−2 mbar (low-vacuum heat-treatment), the electrical resistivity of the AZO target reached the lowest value compared to the other heat-treatment conditions. Subsequently, the AZO thin films with a thickness of 1150 nm were deposited on soda-lime glass substrates by RF magnetron sputtering at room temperature. The XRD patterns of all the as-deposited AZO thin films clearly showed that the thin films had a wurtzite structure with a preferred orientation along the c-axis. Furthermore, the Hall effect measurement results confirmed that the AZO thin film prepared from the low-vacuum heat-treated target had the excellent electrical properties in comparison with the other ones. The optical band gap of the as-deposited AZO thin films was about 3.15 eV and the minimum value of the electrical resistivity was measured about 1.8 × 10−4 Ω cm.