Enhanced gas barrier properties of polymer substrates for flexible OLEDs by adjusting the backbone rigidity and incorporating 2D nanosheets

Abstract

A series of polymer substrates based on the polyimides (PIs) containing diphenylpyridine for flexible OLED displays were successfully fabricated by the incorporation of graphene oxide (GO) and organically modified layered double hydroxide (OLDH) nanosheets. In comparison with pristine PI, the OTR and WVTR of PI nanocomposite films at a loading of 3% OLDH were reduced by 78% and 25.7%, respectively, whereas by incorporation of 0.3% GO, the OTR and WVTR of PI nanocomposite films declined by 85.5% and 31.8%, respectively. The results revealed that GO nanosheets could have a great advantage over OLDH from the aspect of improving the gas barrier performance. Moreover, compared with the pristine PI films (CTE: 4.73 ppm K⁻¹), the incorporation of GO and OLDH nanosheets was of great benefit in reducing the CTE value, such as 1.57 ppm K⁻¹ for PIL-3.0 and 3.33 ppm K⁻¹ for PIG-0.3, while maintaining high T_g values exceeding 450 °C and excellent thermal stability. The resulting PI nanocomposite films showed improved barrier properties without sacrificing the thermal and mechanical performance, and could serve as a promising candidate for substrate materials of flexible OLED displays.