Enhancement of morphological and emission stability of deep-blue small molecular emitter via a universal side-chain coupling strategy for optoelectronic device

Film morphology of emissive layers is crucial to the performance and stability of solution-processable organic light-emitting diodes (OLEDs). Compared to the interpenetration of conjugated polymer chain, small molecular emitter with a flexible side chain always presents easily aggregation upon external treatment, and caused pi-electronic coupling, which is undesirable for the efficiency and stability of deep-blue OLEDs. Herein, we proposed a side-chain coupling strategy to enhance the film morphological an emission stability of solution-processable small molecular deep-blue emitter. In contrary to "parent" MC8TPA, the crosslinkable styryl and vinyl units were introduced as ended unit at the side-chain of CmTPA and OEYTPA. Interestingly, CmTPA and OEYTPA films present a relatively stable morphology and uniform deep-blue emission after thermal annealing (160 degrees C) in the atmosphere, different to the discontinuous MC8TPA annealed film. Besides, compared to the CmTPA and OEYTPA ones, serious polaron formation in the MC8TPA annealed film also negative to the deep-blue emission, according to transient absorption analysis. Therefore, both CmTPA and OEYTPA annealed film obtained at 140 degrees C present an excellent deep-blue ASE behavior with a 445 nm, but absence for MC8TPA ones, associated with the disruption of annealed films. Finally, enhancement of device performance based on CmTPA and OEYTPA film (similar to 40%) after thermal annealing with a similar performance curves also confirmed the assumption above. Therefore, these results also supported the effectiveness of our side-chain coupling strategy for optoelectronic applications. (C) 2021 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.