Benzonitrile-based AIE polymer host with a simple synthesis process for high-efficiency solution-processable green and blue TADF organic light emitting diodes

Abstract

Polymer host materials have great potential for enabling small molecular thermally activated delayed fluorescence (TADF) emitters to construct solution-processed organic light-emitting diodes (OLEDs). Herein, four novel benzonitrile-based polymer hosts, P4CzCN–PA, P4CzCN–BCz (1 : 4), P4CzCN–BCz (1 : 1) and P4CzCN–BCz (4 : 1), with TADF characteristics and simple synthesis processes are fully characterized. All the polymers have high triplet energies (>2.68 eV) for effective exciton confining and AIE property for suppressing exciton quenching. By using homopolymerized P4CzCN–PA as the host material, the solution-processed green and blue TADF-OLEDs achieved the maximum external quantum efficiency (EQE) as high as 20.9% and 13.4%, respectively, which are almost 6 times higher than its copolymerized counterpart. This result demonstrates that the TADF polymer host with AIE property can inhibit its concentration quenching without the need for a complicated copolymerization of the bulky monomer. As far as we know, this is the first report of a benzonitrile-based TADF polymer and the final cost of the polymer is lower without any noble metal catalyst or high boiling point solvent. This strategy of using a benzonitrile-based homopolymer as the host materials of OLEDs provides a direction for the design of easy synthesis and low-cost polymer host materials in the future.