Current status of some electrochromic materials and devices: a brief review

The modern era is an era of science and technology that affects all aspects of life. The simplest physical manifestation of the term 'technology' takes place in the form of a simple and user-friendly device. The design and development of a smart device, capable of performing at its best, depends on the level of scientific understanding of the basic principles that make the actual backbone on which the technology relies. This leads to progressive development and research in electronics, materials science and related fields. An electrochromic device (ECD) is a perfect example of a smart yet very simple form of a device that can be useful for a range of applications, including electrochromism: the phenomenon of bias-induced optical modulation, shown primarily by at least one of the components in an ECD. This article attempts to provide an update on different materials' regimes and highlights the basic requirements that a material must have to be suitable for use as the active component of an ECD. This topical review gives the details of several electrochromic materials, and their electrochemical, electrochromic and other functional properties in brief. An attempt has been made to cover a subset of the vast superset of known electrochromic materials, which can be extended as a detailed comprehensive review in the future. Based on the type(s) of materials used in an ECD, device paradigms are defined, which have also been summarized through different device regimes, namely 'all-organic', 'all-inorganic' and 'hybrid'. A comparative study has also been provided by highlighting advantages and disadvantages of each category of material/device to help one choose a material and device paradigm based on one's requirements. To provide a glimpse, ECDs that are multifunctional and that show other functionalities like memory, and supercapacitive and sensing characteristics have also been mentioned.