A diacetylene-based
thermal cross-linking method for hole-transporting
layers (HTLs) has been investigated. The thin films of 4,4-bis(carbazol-9-yl)biphenyl
(CBP) oligomers functionalized with diacetylene groups were cross-linked
at 150 °C. The cross-linked thin films showed smooth surface
morphologies and solvent stabilities in chloroform, chlorobenzene,
indane, 3,5-dimethylanisole, and so on. The quantum dot light-emitting
diode (QLED) devices based on the cross-linked HTLs displayed high
current density, large maximum brightness, long device lifetime, and
comparable external quantum efficiency in comparison with the corresponding
devices based on the pristine HTLs. The hole-transporting properties
of the cross-linked and the pristine HTLs were also studied in hole-only
devices (HODs). This cross-linking method could be potentially useful
in solution fabrication of multilayer organic electronic devices.