Development of double-layered transparent conducting electrode with thermal stability and thermoelectric materials for high temperature

Abstract

During the fabrication of a thin film photovoltaic device the transparent conducting oxide (TCO), which constitutes an integral part of its basic structure, could be exposed at high temperature processes; in addition, a TCO which could be grown at ambient temperature can be useful in order to minimize possible damages caused to other previously deposited components. Aluminum doped zinc oxide (AZO) is a well-known TCO with good properties in terms of light transparency and conductivity, however its electrical prop-erties deteriorate after subsequent high temperature processes in air atmosphere. In this work, Al doped ZnO (AZO) films were prepared on glass substrate by RF magnetron multi-target sputtering. 2 wt% Al-doped ZnO target was used for the deposition. Al:ZnO films with better texture, high transmission and lower resistivity were obtained for the samples fabricated along c-axis. We realized Al:ZnO films with the better performance by adjusting and optimizing the sputtering power, the target-to-substrate distance and substrate temperature. Firstly, Al:ZnO films were fabricated with various sputtering power and the target-to-substrate dis-tance at room temperature. The optimal condition for deposition of Al:ZnO films with the lowest sheet re-sistance of 6.48 Ω/□ and a transmission toward 85 % in the visible range was obtained at 150 W and 4.5 cm. Then, the films were annealed at 500 oC in air atmosphere for 30 min in order to study their thermal stability. The sheet resistance increased dramatically to 2.41 MΩ/□ after annealing due to oxygen vacancies annihila-tion and Al diffusion. Substrate temperature controlled as the third variable parameter increased from RT to 450 oC. This was done in an effort to understand the influence of the substrate temperature in the thermal stability of Al:ZnO. The films presented better thermal stability along higher substrate temperature. Higher substrate temperature provided energy to deposition atoms to enhance mobili...