Effect of Al3+ ion on the electrochromic and optical properties of TiO2 ultra-thin film

Abstract

Electrochromic materials are capable of reversibly changing their optical properties under an applied electric field, making them suitable for applications in smart windows and display technologies. Titanium dioxide (TiO<inf>2</inf>), a promising EC material due to its dual-band modulation and chemical stability, typically suffers from low Li+ ion interaction. In this study, Al3+ ions are investigated as an alternative to Li+ in ultrathin (5–10 nm) undoped and Mo-doped TiO<inf>2</inf> films deposited via RF magnetron sputtering. Structural, optical, and electrochemical characterizations are performed using GI-XRD, XPS, spectroscopic ellipsometry, and electrochemical techniques. The Al3+ ion-based electrolyte shows superior electrochromic performance, with an optical modulation of up to 52.35 % and coloration efficiency (CE) of 30.18 cm2 C?1, which are significantly higher than those obtained using Li+ (?T: 2.92 %, CE: 3.05 cm2 C?1). While Al3+ ions improve performance, they also contribute to film degradation due to strong Coulombic interactions and the presence of Cl- ions. Mo doping increases the refractive index but does not sufficiently enhance structural stability. This study presents the first demonstration of effective coloration in ultrathin TiO<inf>2</inf> films with Al3+ electrolytes, offering valuable insights for the development of high-efficiency, cost-effective electrochromic devices. © 2025 Elsevier B.V., All rights reserved.