Low-Powered E-Switching Block Copolymer Structural Color Display with Organohydrogel Humidity Controller

Abstract

Soft-solid photonic crystals (PCs) based on periodically ordered block copolymer (BCP) nanostructures demonstrate stimuli-adaptive structural colors (SCs) and desirable mechanical properties suitable for reflective-mode electric-switching (E-switching) displays. However, the low electrochemical stability and humidity-dependent E-switching performance of hygroscopic ionic salts, often employed for E-field-adaptive structural alteration, limit their applications. In this study, a low-powered capacitive E-switching BCP SC display with an organohydrogel (OH) humidity controller is proposed, where a bilayer of a BCP and a polymer blend with hygroscopic E-field-adaptive ionic salts is sandwiched between Au electrodes. The display reliably exhibits reversible full-color E-switching (100 on/off cycles) at operating voltages of +2.5 to -2 V within the ionic salts' electrochemical window at approximate to 50% humidity. A patchable and reusable OH serves as a water reservoir (with optimized geometries and dimensions) to improve the display's humidity tolerance, providing a target humidity (approximate to 50%). The proposed display performs at ambient humidity lower than 60% for over 10 days because of the long water retention and mechanical integrity properties of OH. Additionally, the topologically micropatterned BCP PC allows lateral diffusion of ionic salts through the sides of the patterned domain under E-field, facilitating E-switching speeds of approximate to 30 s.