Decorated pyridine as hole transporting material (HTM) for solution-processed OLEDs

Abstract

While organic light emitting diodes (OLEDs) technology is evolving at a fast pace, the development of flexible and full-color display panels with low power consumption provides superiority to these devices as eco-friendly lighting sources. Several strategies and methods have been attempted to improve the OLED device performance, especially in light-emitting materials. Even though, with significant advancements in efficiency, OLED technology demonstrates the feasibility to enhance further without saturation, thus attracting researchers to develop new materials with an effective device strategy. In this work, we report an integrated hole transporting material, 3,6-bis(4,6-diphenylpyridin-2-yl)-9-ethyl-9H-carbazole (CDP) with functionalization of carbazole unit with pyridine substituents. CDP adopted a moderately high triplet energy (2.61 eV), high thermal stability, and high hole transportability. Solution-processed CDP-based OLEDs were fabricated containing phosphorescent green emitter (Ir(PPy)3) and compared with conventional N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) based OLEDs. The CDP-based device exhibited a high performance with decreased layer thickness from ∼25 nm to ∼5 nm, with maximum external quantum efficiency, power efficiency, current efficiency, and brightness of 17.2 %, 66.8 lm/W, 64.0 cd/A, and 18,740 cd/m2, respectively which was superior to the NPB-based control device. Enhancement in device performance with reduced thickness of hole transport layer in CDP-based OLEDs distinctly demonstrates the effective potential of the designed material.