Classification and Mechanisms of Electrochromic Materials: Advances and Prospect

Abstract

Electrochromic (EC) materials have emerged as promising materials for energy-efficient smart windows and adaptive optical devices due to their ability to reversibly modulate optical properties under electrical stimuli. However, a lack of systematic comparison across different EC materials often leads to ambiguous understanding of their performance trade-offs. To bridge this gap, this paper classifies EC materials (ECs) into four categories: inorganic ECs, organic ECs, hybrid nano-enhanced ECs, and emerging functional ECs, the latter of which include three subcategories: fluorescent ECs, three-layer PANI-based ECs, and dual-band ECs. Each category is discussed in terms of its working mechanism: Inorganic ECs rely on ion insertion/extraction into transition metal oxides, organic ECs involve redox-active conjugated systems and hybrid ECs enhance performance via nanostructuring and interfacial effects, while emerging ECs introduce functionalities such as fluorescence, lateral ion migration, or VIS–NIR dual modulation. By comparing these systems, this paper identifies trade-offs among durability, switching speed, coloration efficiency, and spectral response. Inorganic ECs offer high stability, while organic ECs allow molecular tunability. Hybrid and emerging ECs push the boundaries of performance and multifunctionality. This review highlights the importance of mechanistic understanding to guide material design for next-generation EC technologies.