EL properties of organic light-emitting-diode using TPD derivatives with diphenylstylyl groups as hole transport layer

Abstract We studied the hole transport characteristics of N , N ′-diphenyl- N , N ′-bis (3-methylphenyl)-1,1′-diphenyl-4, 4′-diamine (TPD) derivatives with a variety of diphenystylyl side groups for organic light-emitting-diodes (OLEDs). We newly synthesized three materials. These hole transport materials (HTM) are N , N ′-bis(4-(2,2-diphenylethenyl)-phenyl)- N , N ′-di(p-tolyl)-bendidine (DPS), N , N ′-bis(4-(2,2-di(p-tolyl)ethenyl)-phenyl)- N , N ′-di(p-tolyl)-bendidine (p-mmdps) and N , N ′-bis(4-(2phenyl-2-(p-tolyl)ethenyl)-phenyl)- N , N ′-di(p-tolyl)-bendidine (p-dmDPS). The glass transition points of these materials are 90°C (DPS), no-detection (p-mmDPS) and 180°C (p-dmDPS). DPS thin films did not poly-crystallized after several months at room temperature, whereas TPD thin film poly-crystallized after 1 week. The luminance of the OLEDs (ITO/HTM (50 nm)/Alq 3 (50 nm)/LiF/Al) are 1000 (DPS), 150 (p-mmDPS) and 150 cd/m 2 (p-dmDPS) at 10 V. The current density and luminance of the OLEDs having DPS were not enhanced by the introduction of a 10-nm thick CuPc as a hole injection layer. On the other hand, the current density and luminance of the OLED having p-mmDPS or p-dmDPS were drastically enhanced by introduction of a 10-nm thick CuPc as a hole injection layer, 1750 (p-mmDPS) or 2400 cd/m 2 (p-dmDPS).