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 π-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 °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 °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 (∼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.