Multilayer composite AZO / AGZO thin films for transparent conductive electrodes

Ian Wilkins

Transparent electronics are an essential ingredient in many new technologies which are emerging in the 21st century - high efficiency solar cells [1, 2], interactive and transparent displays, energy efficient windows, and photonics for communications and computing [3]. The development of transparent conductors which are abundant, cheap and environmentally friendly, is critical for materials science in developing such applications. Specifically, an important research goal is to find substitutes for indium tin oxide (ITO) - the dominant transparent conductive oxide (TCO) material. ITO is a high performing and robust transparent conductor, but it is made from indium which is scarce, expensive and toxic. Zinc oxides doped with small amounts of aluminium (AZO), are promising candidates for such a substitute but generally don’t perform as well as ITO [3]. Gallium co-doping with aluminium improves AZO performance significantly, but raises similar concerns to ITO, in terms of the scarcity and high cost of gallium. This project aims to enhance the conductivity of AZO thin films, by adding a thin middle layer, co-doped with Ga (AGZO). The project employed the solution based sol-gel technique for synthesising AZO and AGZO nanoparticles, and then deposited composite multi-layered thin films on glass substrates using a spin coating process. The optical properties, crystal structure and morphology of the films were characterised using UV-vis and FTIR spectroscopy, X-ray diffraction and Field Emission Scanning Electron Microscopy. Composite multilayer films were produced with thickness around 320nm, exhibiting transmittance above 90% across the visible range and resistivity approximately 10 Ωcm. Results indicate significant improvement in AZO films, resulting from the addition of the co-doped AGZO mid-layer. The enhancement in performance recorded, was 4 similar to that found in uniformly doped AGZO films, except that the composite films contained only 20% of the gallium compared with the AGZO films. Due to the high cost of gallium, this presents the potential for significant reduction in the materials cost for TCO thin films.

Multilayer composite AZO / AGZO thin films for transparent conductive electrodes

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