Lewis Acid-Doped Conjugated Polymer Nanolayers for Efficient Hole Injection in Phosphorescent Organic Light-Emitting Devices

초록

Here, we demonstrate that the hole injection characteristics of phosphorescent organic light-emitting devices (OLEDs) can be greatly improved by introducing a Lewis acid-doped conjugated polymer nanolayer. Tris(pentafluorophenyl)borane (BCF) and poly(3-hexylthiophene) (P3HT) were employed as a Lewis acid and conjugated polymer, respectively. The color of P3HT solutions quickly changed to a deep purple upon addition of BCF regardless of the BCF molar ratio, while optical absorption peaks (wavelength = 650-1100 nm) were measured for the BCF-doped P3HT (P3HT:BCF) films. The surface and electronic structures of P3HT:BCF nanolayers were examined with atomic force microscopy (AFM) and ultraviolet photoelectron spectroscopy (UPS), respectively. The electron spin resonance (ESR) spectroscopy was used to prove the existence of single (unpaired) electrons in the P3HT:BCF films. The phosphorescent OLEDs with the P3HT:BCF nanolayers showed a remarkable enhancement of luminance from ca. 575 cd/m(2) (BCF = 0 mol %) to 26,910 cd/m(2) (70 mol %), leading to a high current efficiency of ca. 19 cd/A (70 mol %).

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