Combining molecular encapsulation and an AIE strategy to construct an efficient blue TADF polymer for solution-processed multilayer white OLEDs

Abstract

Polymerization can achieve new powerful systems through the integrated assembly of components. However, when thermally activated delayed fluorescence (TADF) properties are transferred into a polymer, the compact molecular chain will inevitably induce strong interactions between TADF units, resulting in a severe fluorescence quenching effect. Here, molecular encapsulation and an aggregation-induced emission (AIE) strategy were combined for constructing a TADF polymer with sufficient suppression of the exciton quenching effect in a condensed solid state. The resulting novel polymer P-Cz4CzCN exhibits a smaller ΔE_ST value and obviously enhanced PLQY compared to its unencapsulated counterpart P-4CzCN in neat film. Solution-processed OLEDs achieve maximum EQEs of 11.5% and 13.0% for sky-blue and hybrid white devices, respectively, which are among the highest efficiencies ever reported for TADF polymer devices without dependence on a small molecular host. Additionally, such an encapsulated AIE TADF polymer can fully utilize the advantages of morphological stability and solvent resistance to enable a fully-solution-processed device through an orthogonal solvent, while the emission layer of the control device was totally washed away and failed without any detected electroluminescence signal. Although this is the first attempt to use a TADF polymer to construct fully-solution-processed monochrome and composite white OLEDs, the design idea of combining molecular encapsulation and an AIE strategy will be an important stepping stone for further enhancing device performance and broadening the application areas of TADF polymers.