High-Efficiency Deep-Blue Solution-Processed Organic Light-Emitting Diodes Using Carbazole Dendrons Modified Hybridized Local and Charge-Transfer Emitters

Abstract

In the pursuit of efficient and cost-effective organic light-emitting diodes (OLEDs), the development of solution-processed hybridized local and charge transfer (HLCT) emitters presents a promising approach. HLCT materials uniquely integrate the advantages of both singlet and triplet excitons, surpassing the traditional spin statistical limit of 25 % while offering high photoluminescence efficiency and balanced charge transport properties. Herein, we report the synthesis and characterization of two new deep blue, solution-processable HLCT fluorophores, G1FTPI and G2FTPI. These compounds incorporate fluorenyl carbazole dendron units into the HLCT luminogenic triphenylamine-phenanthroimidazole (TPI) molecule. Their HLCT and photoluminescence (PL) properties were experimentally and theoretically investigated using solvation effects and density functional theory (DFT) calculations. The molecules exhibit deep blue emission with a high solid-state fluorescence quantum yield, good solution-processed film-forming quality, and high hole mobility values of 2.18–2.61×10⁻⁶ cm² V⁻¹ s⁻¹. Both compounds were successfully employed as non-doped emissive layers in solution-processed OLEDs, demonstrating excellent electroluminescent (EL) performance. Notably, the G2FTPI-based device emitted a deep blue light at 432 nm with CIE coordinates of (0.158, 0.098) and achieved a maximum current efficiency (CE_max) of 3.13 cd A⁻¹ and a maximum external quantum efficiency (EQE_max) of 5.30 %.