Multifunctional Reversible Electrochromic Mirror Enabled by Sn-Doped In ₂ O ₃ Nanoparticles-Coated Roughened ITO Double-Layer Electrodes

A multifunctional reversible electrochromic mirror (REM) device capable of four distinct optical states–transparent, black, mirror, and multicolor– is demonstrated for next-generation smart window applications. The device adopts a transparent electrode-sandwiched configuration composed of an Sn-doped In 2 O 3 (ITO) nanoparticle (NP) layer coated on a flat ITO substrate and a smooth amorphous InGaTiO (IGTO) electrode. The roughened ITO double layer (ITO NP/ITO film), exhibiting a root-mean-square roughness of 18.26 nm, promotes black-state formation through enhanced light absorption induced by the localized surface plasmon resonance of selectively deposited Ag NPs. Coupled with an atomically smooth IGTO electrode, these complementary surfaces enable robust and reversible optical switching via electrochemical redox reactions within the Ag–Cu gel electrolyte. The REM device maintains stable modulation across all states for over 250 consecutive cycles and achieves dynamic multicolor switching through step-voltage control. This combination of tunability, stability, and multifunctionality highlights the strong potential of the proposed REM platform for advanced electrochromic systems and smart window technologies for buildings and automobiles.