Enhanced flexibility of WO₃-based flexible electrochromic devices for smart windows via ion beam treatment

A flexible electrochromic (EC) device was developed using amorphous WO₃ as the electrochromic layer and amorphous InGaTiO (IGTO) as the electrode, both deposited by magnetron sputtering on a polyethylene terephthalate (PET) substrate. To enhance the adhesion of the IGTO electrode to the PET substrate, oxygen ion beam treatment (IBT) was employed to modify the surface structure of the PET. The imporved adhesion between the amorphous IGTO/WO₃ layers and PET substrarte enhanced the performance of EC device. The IBT-treated PET/IGTO/WO₃ device demonstrated an optical contrast of 81.35 % and a coloration efficiency (CE) of 48.23 cm²/C, which is an improved performance compared to the optical contrast of 75.69 % and CE of 32.86 cm²/C before ion beam treatment. In the IBT-treated EC device remained stable over 500 chronoamperometry (CA) cycles, unlike the pre-treatment device. Furthermore, the flexbile EC device withstood a fatigue bending test of 10,000 cycles, maintaining approximately 80 % of its performance. These results indicate that the surface-modified PET/IGTO/WO₃ structure offers a stable, reliable, and flexible EC device. Possible mechanism of the IBT was suggested to explain the improved mechanical properties and performances of flexible EC devices.