Al3+ intercalation/de-intercalation-enabled dual-band electrochromic smart windows with a high optical modulation, quick response and long cycle life

Abstract

Dual-band electrochromic smart windows with independent control of the transmittance of near-infrared (NIR) and visible (VIS) light can contribute significantly to the reduction of building energy consumption. Cost and inadequate electrochromic performance are the current technical challenges. We present here a dual-band electrochromic smart window design based on the intercalation/de-intercalation of Al³⁺ cations to replace the common use of monovalent cations in electrochromic applications. The Al³⁺ intercalation/de-intercalation-enabled electrochromic smart window delivers not only efficient and independent control of NIR and VIS light transmittance, but also impressive electrochromic performance – a high optical modulation of the full solar spectrum (93.2%, 91.7%, 88.5%, and 86.8% at 633, 800, 1200, and 1600 nm, respectively), high coloration efficiencies (254 and 121 cm² C⁻¹ at 1200 and 633 nm, respectively), fast switching times (8/5 s and 16/13 s at 1200 and 633 nm, respectively, for coloration/bleaching), and high bistability and cyclability (a 5.5% capacity loss after 2000 cycles). The good electrochromic performance can be attributed to the effective diffusion of Al³⁺ in the electrochromic material (as good as that of Li⁺); and a shallow intercalation/de-intercalation depth enabled by the ability of Al³⁺ to support three-electron redox reactions. The performance of Al³⁺ intercalation/de-intercalation-enabled dual-band electrochromism was also verified in laboratory prototype devices to confirm its suitability for dual-band smart windows.