Colloidal electrochromic photonic crystals: Insights into materials, mechanism, and performance enhancement

Colloidal electrochromic photonic crystals (EPCs) are optical material which changes their photonic band gap and structural colors under electric field due to the electrophoresis of colloidal particles. They have attracted great interest in recent years because of their great potential in color displays, smart windows, adaptive camouflage, and various functional devices. This review aims to introduce the fundamentals and recent progress of colloidal EPCs, which include the chemical composition and synthesis, the physical characteristics, the electrochromic mechanism, and the evaluation standards. Meanwhile, this review also summarizes the effective approaches to enhance the EPC performances from the perspective of colloidal particles, dispersant, electrode, and driving waveforms. Challenges and perspectives are finally provided for the future development of colloidal EPC materials.