Microcontact printing of self-assembled monolayers to pattern the light-emission of polymeric light-emitting diodes

By patterning a self-assembled monolayer (SAM) of thiolated molecules with opposing dipole moments on a gold anode of a polymer light-emitting diode (PLED), the charge injection and, therefore, the light-emission of the device can be controlled with a micrometer-scale resolution. Gold surfaces were modified with SAMs based on alkanethiols and perfluorinated alkanethiols, applied by microcontact printing, and their work functions have been measured. The molecules form a chemisorbed monolayer of only similar to 1.5 nm on the gold surface, thereby locally changing the work function of the metal. Kelvin probe measurements show that the local work function can be tuned from 4.3 to 5.5 eV, which implies that this anode can be used as a hole blocking electrode or as a hole injecting electrode, respectively, in PLEDs based on poly(p-phenylene vinylene) (PPV) derivatives. By microcontact printing of SAMs with opposing dipole moments, the work function was locally modified and the charge injection in the PLED could be controlled down to the micrometer length scale. Consequently, the local light-emission exhibits a high contrast. Microcontact printing of SAMs is a simple and inexpensive method to pattern, with micrometer resolution, the light-emission for low-end applications like static displays.