Characteristics of phosphorescent organic light-emitting devices with interfacial nanolayers of acid molecule-doped tris(4-aminophenyl)amine

Abstract

Here we report that 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-doped tris(4-aminophenyl)amine (TAPA) can act as an interfacial layer for hole injection in phosphorescent organic light-emitting devices (OLEDs) and deliver improved device stability upon electric fields. The acid-base reaction between TAPA and AMPSA was carried out using 2-methoxy ethanol solvent with various molar ratios (0–300 mol. %). The resulting TAPA:AMPSA layers (1–10 nm thick) were spin-coated on indium-tin-oxide (ITO)-glasses and selectively annealed before the thermal deposition of organic small molecular multilayers in a vacuum. The doping reaction between TAPA and AMPSA gave rise to a new absorption peak at a wavelength of ca. 880 nm. The work function of TAPA:AMPSA layer-coated ITO-glasses increased with the molar ratio, but the highest luminance and efficiency of OLEDs were achieved at 100 mol. % (AMPSA to TAPA). The thickness control and thermal treatment process of TAPA:AMPSA layers (100 mol. %) could further enhance the luminance (from ca. 5000 cd/m2 (t = 10 nm) to 15,500 cd/m2 (t = 2 nm)) with relatively high device stability upon electric field compared to the pristine TAPA layers.