Electrochromic Devices Based on 2D MoO_3-x/PEDOT:PSS Composite Film with Boosted Ion Transport

Electrochromic materials allow for optical modulation and have attracted much attention due to their bright future in applications such as smart windows and energy-saving displays. Two-dimensional (2D) molybdenum oxide nanoflakes with combined advantages of high active specific surface area and natural layered structure should be highly potential candidates for electrochromic devices. However, the efficient top-down preparation of 2D MoO₃ nanoflakes is still a huge challenge and the sluggish ionic kinetics hinder its electrochromic performance. Herein, we demonstrated a feasible thiourea-assisted exfoliation procedure, which can not only increase the yield but also reduce the thickness of 2D MoO_3-x nanoflakes down to a few nanometers. Furthermore, electrophoretic-deposited MoO_3-x nanoflakes were combined with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-conjugated polymer to simultaneously enhance the ionic kinetics and electronic conductivity, with a diffusion coefficient of 3.09 × 10^-10 cm² s^-1 and a charge transport resistance of 33.7 Ω. The prepared 2D MoO_3-x/PEDOT:PSS composite films exhibit improved electrochromic performance, including fast switching speed (7 s for bleaching, 5 s for coloring), enhanced coloration efficiency (87.1 cm² C^-1), and large transmittance modulation (ΔT = 65%). This study shows outstanding potential for 2D MoO_3-x nanoflakes in electrochromic applications and opens new avenues for optimizing the ion transport in inorganic-organic composites, which will be possibly inspired for other electrochemical devices.