Solution-Processed Oxide-Semiconductor Films and Devices

Abstract

Over a past decade, transparent conducting oxide (TCO) thin films have gained much attentions for application in electronic devices including sensors, solar cells, thin-film transistors and flat panel display due to their excellent properties such as high mobility, low resistivity, high transmittance in visible region, high transparency in infrared region. Hitherto, the indium tin oxide (ITO) is one of the most commonly used TCO materials in electronic devices owing to its low resistivity (≤ 10−3 Ω cm), low processing temperature (~250oC) and high optical transparency (> 80%) in visible region. However, the ITO material has some drawbacks owing to scarcity, toxicity, and high production cost of indium, and it is necessary to develop the indium-free materials for replacing ITO. Among various indium-free materials, ZnO-based thin films have been extensively known as one of the most potential materials for replacing ITO in electronic devices because of their abundance, non-toxicity, high conductivity, high transparency in visible region and low cost. On the other hand, CuO-based thin films have been also known as a typical p-type semiconductor, possessing a narrow band gap energy near 2.1 eV, having monoclinic structure and being grouped in abundant non-toxic materials. In general, the CuO thin films are considered for promising applications in catalyst, semiconductor devices and energy stored batteries. Owing to their narrow band gap, the CuO thin films are possibly applied to expand the light harvest from ultraviolet to visible regions, which indicates superior photo-catalytic efficiency. Also, the CuO thin films enable to design as a hole-transport visible-light absorber layer in solar cells. From this point of view, the light absorption ability of CuO thin film plays a key role in photo-catalytic experiment or solar cell production. It means that this kind of materials would be promising for the new options of p-type materials in various applications in electronic industry.In this chapter, therefore, we discuss on the conventional oxide-semiconductor materials and devices, compare with the recent developments on the new generation of both n-type and p-type semiconductor thin films, then orient for the selection of friendly environmental materials. Eventually, we discuss on the recent achievement of device applications such as thin-film transistors and all solution-processed inorganic solar cells.