Introducing electron-rich thiophene bridges in hot exciton emitter for efficient non-Doped near-infrared OLEDs with low turn-on voltages

Abstract

The development of near-infrared (NIR) luminescent materials featuring high photoluminescence quantum yield (Φ_PL) at aggregated state is of great significance for achieving highly efficient non-doped organic light-emitting diodes (OLEDs) but remains formidable challenging. Herein, a design strategy of introducing electron-rich thiophene groups between electron acceptor and donor is proposed for efficient NIR luminescent materials, and a tailored D-π-A-π-D type emitter, namely, 4,4′-(benzo[c][1], [2], [5]thiadiazole-4,7-diylbis(thiophene-5,2-diyl))bis(N,N-diphenylaniline) (TPATBT), is designed and prepared. The photophysical investigation and density functional theory analysis disclose that TPATBT is a hot exciton emitter feature with hybridized local and charge-transfer state. Additionally, TPATBT demonstrates aggregation-induced emission characteristic, prefers high thermal stability, and exhibits a strong emission at 692 nm with a decent Φ_PL of 20 % in the neat film. The non-doped device based on TPATBT neat film presents a maximum external quantum efficiency (η_ext,max) of 1.22 % with electroluminescence peak at 718n m. Moreover, we first try to use interlayer sensitization to sensitize non-doped devices, which achieves better η_ext,max of 1.34 % with low turn-on voltage of 3.2 V. The proposed molecular design strategy in this work is promising for exploring robust NIR luminescent materials for high-performance OLEDs.