Controllable and large-scale fabrication of flexible ITO-free electrochromic devices by crackle pattern technology

Abstract

Electrochromic devices (ECDs) presenting reversible color variation are considered as the most promising alternative to traditional smart windows. However, the fabrication of large-scale ECDs with high flexibility and stability is still challenging. In this work, we present a crackle pattern technology for controllable and large-scale fabrication of rectangular Ag network films for indium tin oxide-free (ITO-free) flexible ECDs. This rectangular Ag film exhibits superior mechanical robustness and controllable optoelectronic performance (2.0 Ω sq⁻¹ at 91% transmittance). In the application of WO₃ based ECD, the rectangular film presents an ultrafast switching time (0.25/0.18 s for bleaching/coloring) and is thus applicable in flexible displays. Moreover, this device demonstrates a large optical modulation of 76% at 630 nm and sustains 78.9% of its initial modulation even after 20 000 cycles, which is close to the commercial standard for rigid ECDs. The obtained rectangular Ag films are successfully assembled into a flexible all-solid-state ECD (21 × 13 cm²), which can be utilized in smart windows, glasses and other fields that require bending or cutting.