Flexible organic light-emitting diode (OLED) devices based on polymer substrates have attracted worldwide attention. However, the current OLED polymer substrates are limited due to weak thermal stability, which is not compatible with the high temperature in OLED fabrication. Here, we developed a novel nanocellulose/polyarylate (PAR) hybrid polymer substrate with both high transparency and excellent thermal properties. Benefiting from the nanometer scale of the cellulose nanofibrils (CNFs) and the efficient interfacial interaction with PAR, the substrate exhibited greatly improved thermal stability, with a glass transition temperature of 192 °C, the thermal decomposition temperature of 501 °C, and upper operating temperature up to over 220 °C. Meanwhile, the hybrid substrate exhibits outstanding mechanical properties. Notably, no apparent transparency loss was observed after the CNF addition, and the hybrid substrate maintains a high transmittance of 85% and a low haze of 1.75%@600 nm. Moreover, OLED devices fabricated on the hybrid substrates exhibit a much improved optoelectrical performance than that of the devices fabricated on the conventional poly(ethylene terephthalate) (PET) substrates. We anticipate this research will open up a new route for fabricating flexible high-performance OLEDs.

Flexible organic light‐emitting diode (OLED) displays have attracted worldwide attention and colorless polyimides (CPIs) are their key substrate materials. However, desirable CPIs are difficult to obtain since the thermal and mechanical properties are sacrificed during CPI production through modification of colored polyimide. Here, a cellulose nanocrystal (CNC)/CPI hybrid substrate with high optical, mechanical, and thermal properties is introduced. Due to the outstanding mechanical and thermal properties of CNCs as well as their strong interfacial interaction with CPI matrix, the sacrificed properties are made up and hybrid substrate is demonstrated strikingly improved thermal properties and mechanical properties with thermal decomposition temperature of 555 °C, upper operating temperature of 320 °C, glass transition temperature of 289 °C, coefficient of thermal expansion of 31.62 ppm K−1, tensile strength of 128 MPa, elastic modulus of 3.72 GPa, and folding capacity of 160 000 times. Particularly, the substrate keeps an excellent transmittance of 86% at 600 nm and it is colorless. The OLED devices built on the hybrid substrates show outstanding performance, which is superior to that of OLED@CPI, and comparable to that of OLED@glass. It is expected that this work will open new avenues for fabricating high‐performance and low‐cost flexible OLED devices.

For flexible electronics, the substrates play key roles in ensuring their performance. However, most substrates suffer from weak bonding with the conductive ink and need additional aids. Here, inspired by the Ag−S bond theory, a novel cellulose nanopaper substrate is presented to improve the bond strength with the Ag nanoparticle ink through a facile printing method. The substrate is fabricated using thiol-modified nanofibrillated cellulose and exhibits excellent optical properties (∼85%@550 nm), ultra-small surface roughness (3.47 nm), and high thermal dimensional stability (up to at least 90 °C). Most importantly, it can attract Ag nanoparticles initiatively and bind them firmly, which enable the conductive ink to be printed without using the ink binder and form a strong substrate−ink bonding and maintain a stable conductivity of 2 × 10 −4 Ω cm even after extensive peeling and bending. This work may lead to exploring new opportunities to fabricate high-performance flexible electronics using the newly developed nanopaper substrate.

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