Electrical properties of aluminum-doped zinc oxide for applications in solar cells

• Main Author: Liu, Wenlong.
• Other Authors: Sam Zhang Shanyong
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Mechanical engineering::Alternative, renewable energy sources
• Online Access: http://hdl.handle.net/10356/17167
• Institution: Nanyang Technological University

Transparent conductive oxides (TCO) are indispensable as front contact for most of the thin film solar cells. In consideration of low cost and environmental friendliness, aluminum-doped zinc oxide (ZnO:Al) is one of the most suitable TCO candidates. In the present work, thin films of aluminum-doped zinc oxide were prepared by magnetron sputtering on glass substrates as a function of the few deposition conditions suggested. The electrical properties of the films of sputtered ZnO:Al were measured using Van der Pauw Measurement configuration. It is found that the electrical properties of the sputtered ZnO:Al films shows weak dependence on its film thickness. However, the properties of the films reflects strong dependencies on deposition parameters such as deposition working pressure, starting substrate temperature, power input and oxygen flow rate used. In terms of power input on the targets and deposition working pressure, they are found to influence the Al doping concentration in the films, which can directly affect the electrical transport properties of the ZnO:Al thin films. Whereas for the increased oxygen flow rate and high starting substrate temperature, both deposition parameters result in the decreased oxygen vacancies in the films, causing the rise in resistivity. Post-growth modification of the sputtered ZnO:Al films was carried out by annealing the ZnO:Al films in air so as to investigate the effect of annealing on the electrical properties of the films. Annealing of the ZnO:Al films in ambient environment gives rise to increased resistivity, and decreased mobility as well as carrier concentration. This is also due to the decreased oxygen vacancies in the films.