Characteristics of AZO electrode with high transmittance in near infrared range

We studied Al2O3-doped ZnO (AZO) thin film as a transparent conducting layer for photovoltaic cell operated in wide range of solar spectrum. Effects of substrate temperature on the optical, structural, and electrical properties of thin AZO film were investigated. AZO films were deposited on glass substrates by RF magnetron sputtering system using a 2 wt.% Al2O3 doped target at different temperature conditions. The grown AZO films at low deposition temperatures ranged from 100 degrees C to 300 degrees C show relatively low resistivity, while the samples deposited at 400 degrees C or room temperature are with higher resistivity of -8 x 10(-4) Ω x cm. The measurement by atomic force microscopy reveals that all AZO films possess very smooth surface morphologies with RMS values below 1 nm regardless of substrate temperature. Optical transmittance of the AZO films increases from 81% to 95% as the substrate temperature increases. The AZO films deposited at 200 degrees C condition shows the optimum value of figure-of-merit of 43.7 x 10(-3) Ω(-1), showing the resistivity of 3.4 x 10(-4) Ω x cm and the transmittance of 94%. Additionally, it is noted that the transmittance of the films at near infrared wavelength of 1250 nm exceeds 90%, demonstrating the feasibility as a transparent electrode for thin film solar cell with narrow band gap.