A solution-processable hybridized local and charge-transfer (HLCT) phenanthroimidazole as a deep-blue emitter for efficient solution-processed non-doped electroluminescence device

Abstract

Most highly efficient hybridized local and charge-transfer (HLCT)-based organic light‐emitting diodes (OLEDs) are multi-layer devices fabricated by thermal vacuum evaporation techniques, which are inappropriate for the simplified device fabrication process. However, there are only a couple of reported examples of solution-processed HLCT OLEDs, particularly deep-blue OLEDs. Herein, we design and synthesize a solution-processable HLCT emitter, CPPI, in which 1,2-diphenyl-phenanthroimidazole (PI) as an acceptor core is substituted by three 3,6-di-tert-butyl-N-phenyl-carbazole (CP) moieties as a donor and hole-transporting/solubilizing unit. The HLCT and photophysical properties are thoroughly examined by theoretical and experimental methods. CPPI exhibits HLCT characteristics with intense deep-blue color emission, high thermal and electrochemical stability, and decent hole-transporting ability. The molecule is successfully fabricated as a solution-processed non-doped emitter in organic light-emitting diodes (OLED). The solution-processed OLED retains efficient and stable deep-blue color emission (CIE coordinates of (0.157, 0.089)) with a narrow FWHM of 66 nm, an EQEmax of 3.39% and a high exciton utilization efficiency of 42.4%. Crucially, this result signifies an advance in developing a solution-processable HLCT molecule as an emitter for solution-processed non-doped OLEDs.