28‐3: Degradation of Organic Molecular Complex Dependent on Atmosphere

Abstract

In order to understand instability occurring in OLED devices, time‐dependent atmospheric denaturalization studies of π‐conjugated DNTPD (N1,N1′‐(biphenyl‐4,4′‐diyl)bis(N1‐phenyl‐N4,N4‐di‐m‐tolylbenzene‐1,4‐diamine) thin films, functioned as a hole injection layer in OLEDs, and its effect on device performances were described. The formation of C‐OH (DNTPD‐OH) and C=O (DNTPD=O) bonds were supported by the density functional theory (DFT) calculations. With increasing the air‐exposure time, the DNTPD thin film stored in air (23 °C, 55%RH, dark room) became thicker and bumpy; aromaticity was rapidly diminished; relative atomic amount of carbon and nitrogen were continuously decreased, on the contrary, that of oxygen was gradually increased. The atmospheric denaturalization in DNTPD films includes the formation of hydration layer, oxidation and degradation of DNTPD molecules by attacks of reactive hydroxyl ions existed in the air and formed by self‐ionization of water, and volume expansion due to interpenetration of water between the DNTPD molecules. The OLED devices made of air exposed DNTPD thin films as a hole injection layer showed degraded device performances compared with the air‐free device, resulting from the disturbed energy diagram and degraded hole transport property by the oxidized/degraded DNTPD molecules.