Nanostructured tungsten oxide thin film devices: from optoelectronics and ionics to iontronics

Abstract

Tungsten oxide, as a typical functional transition metal oxide semiconductor, has been widely and intensively investigated for various applications. This review focuses on the recent progress of nanostructured tungsten oxide thin film devices, ranging from optoelectronics and ionics to iontronics. The recent research results on structural, defect, and ion intercalation aspects of tungsten oxide are first introduced in the review, as they are fundamental to the understanding and design of tungsten oxide devices. This part stresses the correlation between these aspects of tungsten oxide and its electronic structures. Then nanostructured tungsten oxide thin film devices are reviewed, especially photodetectors, electrochromic and supercapacitive devices, memristors and electrolyte-gated transistors. The figures of merit of the reported tungsten oxide photodetectors are comprehensively compared, analysed and summarised. New fabrication methods, novel configurations, multiple functions, and mechanism investigations of tungsten oxide electrochromic and supercapacitive devices are emphasized. In the exciting development of emerging iontronics, which bridges electronics and ionics, the operating mechanisms and performance of tungsten oxide-based memristors and electrolyte-gated transistors are underlined. The development trends, challenges, and opportunities of nanostructured tungsten oxide thin film devices are also analyzed and proposed.