Blue polyimides for high-performance solution-processable organic light-emitting diodes

Abstract

Blue light-emitting materials with excellent film-forming ability, superior morphological stability, outstanding color purity, and high device efficiency are in urgent demand for new-generation display and solid-state lighting devices fabricated by low-cost wet processing. However, their current performances are far from satisfactory. Herein, two polyimide (PI)-based blue polymers are first precisely constructed and synthesized through a “Hinge-type Linking” strategy. A small molecular is introduced into the PI backbone via non-conjugated aliphatic imide ring linker. These polymers not only show superb thermal stability and morphological stability, but also maintain narrowband blue emission. Furthermore, PIs are prepared by polycondensation method, precipitated and purified in ethanol solvent, which avoids the use of metal catalysts. The resulting solution-processable devices achieve high performance with a maximum external quantum efficiency (EQE) of 9.94 % and maximum emission peak at 460 nm. To the best of our knowledge, this is the first time that solution-processable polymer light-emitting diodes (PLEDs) based on the “hot exciton” mechanism achieving splendid performance with maximum EQE close to 10 %. The superior performance is attributed to the validity of the “Hinge-type Linking” strategy in PLEDs, opening up a new avenue for PLED development and application.