Inhibition of solution-processed 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile crystallization by mixing additives for hole injection layers in organic light-emitting devices

Abstract

We report the inhibition of solution-processed 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) crystallization by mixing additives for the hole injection layers (HILs) in organic light-emitting devices (OLEDs). Various additives were mixed with the HAT-CN layer, including acrylates, compounds resembling HAT-CN and arylamine derivatives. Among these, the HAT-CN films mixed with ditrimethylol propane tetraacrylate (AD-TMP) and pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN) showed a transparent appearance and high solvent resistances. The former was ascribed to the inhibition of the crystallization. We used these additives for the preparation of electron acceptor layers in charge generation layers (CGLs) of the CGL-only devices. The device prepared by mixing HAT-CN with PPDN showed a lower driving voltage and was applied to the production of an HIL in a solution-processed OLED. The device showed a lower driving voltage and a higher luminescent efficiency than those of the device containing a conventional HIL, poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS). The inhibition of solution-processed 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) crystallization by mixing additives was successfully achieved for hole injection layers (HILs) in organic light-emitting devices (OLEDs). Among various additives, the film mixed with pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile (PPDN) showed both transparent appearance and high solvent resistances to an upper layer coating solvent. We applied the HAT-CN mixed with PPDN for an HIL in an OLED including solution-processed four-layer stack. The device showed lower driving voltage and higher luminescent efficiency than a device containing conventional HIL, poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT:PSS).