Binary Solvent Effects on Thermally Crosslinked Small Molecular Thin Films for Solution Processed Organic Light-Emitting Diodes

Abstract

Solution processing of crosslinkable small molecular thin films is potentially attractive for the fabrication of large-area display panels based on organic light-emitting diodes (OLEDs). The characteristics of a wet-processed film made of a thermally crosslinked small-molecular material can be controlled by simply adding a cosolvent to its solution. The surface morphology of a nanometer-scale thin film made of N4,N4′-di(naphthalen-1-yl)-N4,N4′-bis(4-vinylphenyl)biphenyl-4,4′-diamine (VNPB), dissolved in chlorobenzene, improved dramatically after the addition of 20% cyclohexanone. At the same time, better resistance of the crosslinked layer to a number of solvents frequently used in the fabrication of the adjacent emitting layer was achieved. Moreover, the maximum current efficiency in the binary solvent device increased significantly to 22.2 Cd/A, compared to 9.7 Cd/A in the reference device without VNPB, and the device lifetime was extended by up to 74.8%. This illustrates a simple and additive-free strategy to prevent the formation of defects in solution processed thin-film stacks made of small-molecular materials. The insights gained will be helpful in the solution-based manufacture of large-area OLEDs and other optoelectronic components.