Crosslinkable hole-transport layer on conducting polymer for high-efficiency white polymer light-emitting diodes

The high-efficiency polymer white organic light emitting diodes (WOLED) using a hole injection/transport bilayer was formed by thermally crosslinking a tris(4-carbazol)triphenylamine (TCTA)-based hole-transport layers (HTL) on top of a PEDOT:PSS layer. A TCTA derivative with two cross-linkable vinylbenzyl (VB) ether groups was synthesized with double bond on VB ether groups polymerized at the temperature above 150°C. The results show that the uniform films formed on the top of predried PEDOT:PSS layer, retained a mirrorlike smoothness, after thermally cured at 180°C for 30 min. The VB-TCTA above the interfacial region functions as a spacer to prevent the PEDOT:PSS chain and other mobile constituents from penetrating into the light emitting layers (EML)and quenching the emission. The excellent solvent resistance of the fully crosslinked HTL ensures the subsequent solution processing of the EML.