Ink-jet-printed semiconductor electrochromic nanoparticles: Development and applications in electrochromism

Printed-electronics emerged as an important feature to introduce electronic devices in a great variety of substrates, from paper to glass, such as transistors, light-emitting devices (LEDs), and electrochromic devices (ECD). The technological demand represents a great opportunity for the introduction of intelligent functional materials in our everyday life. Ink-jet printing is a key player due to its low cost, flexibility, high resolution, efficient depositions, and scale up to large areas. It allows fine control of the deposition of the different materials required to assemble an ECD, in position, patterning, and film thickness. ECDs are multilayer-type devices, with two transparent electrodes, a so-called electrochromic layer deposited on each electrode and an intermediate electrolyte layer resembling the structure of a battery. The electrochromic layer is made of semiconductors, normally metal oxides (e.g., WO₃, NiO) or organic polymers such as polythiophenes (e.g., PEDOT, poly(3, 4-ethylenedioxythiophene)). In this chapter, we demonstrate the use of ink-jet printing for the deposition of the electrochromic layers by preparing stable inks of semiconductor nanoparticles and their potential for applications in light management, such as electrochromic windows, and color switching of labels/safety tags.