Fabrication of flexible transparent paper substrate via epoxy resin impregnation and luminescence enhancement through synergistic action of high transparency and desirable haze of substrate for LEC devices

In this study, we present a novel method for fabricating flexible transparent paper substrates via epoxy resin impregnation and coating, which exhibit high transparency (90.98 %) and desirable haze (41.5 %). In this method, the epoxy resin with a refractive index close to that of cellulose fibers, is employed to effectively fill the porous structure of the paper substrate, significantly enhancing the transparency of the substrate while maintaining an appropriate haze. This not only allows for more light transmission but also facilitates light absorption and scattering at wide angles, improving the optical coupling efficiency for light-emitting devices. Additionally, the fibers in the substrate provide the skeletal structure, whilst the fiber encapsulation by the epoxy enhances the mechanical properties and chemical stability of the substrate. Simultaneously, due to the interfacial interlocking and hydrogen bonding of the conductive PEDOT:PSS spin-coated with its interacting substrate, it forms a flexible PEDOT:PSS electrode having stable physical and chemical performance. Finally, based on the excellent optical and mechanical properties of the prepared substrate, we successfully fabricate light-emitting electrochemical cells (LECs) through an all-solution processing method under ambient conditions. The LECs on the transparent paper substrate achieve superior maximum luminance (L_max = 1082.4 cd m⁻²) and current efficiency (CE_max = 1.14 cd A⁻¹), surpassing those of devices prepared on conventional PET. This work proposes a novel method for the preparation of a low-cost and high-performance substrate.