PHOTOPROCESSED AND MICROPATTERNED CONJUGATED POLYMER LEDS

We present a detailed study of the effect of fabricating light-emittin g diodes (LEDs) containing conjugated polymers, using photolithographi c processing; a technique more conventionally used in inorganic semico nductor device manufacture. It is shown that for the specific poly(2,5 -dialkoxy-p-phenylenevinylene) used here, the photoprocessing procedur e chemically modifies the polymer, resulting in an increase in the deg ree of conjugation and a concomitant reduction in photoluminescence qu antum efficiency to 35% compared to an unprocessed film. A similar red uction in electroluminescence quantum efficiency indicates that this i s also the dominant effect in photoprocessed LEDs. LED device characte ristics show an increase in threshold field for the photoprocessed dev ices suggestive of the formation of a barrier layer at the polymer/cat hode interface, resulting in a further partial reduction in device pow er efficiency. There are however no catastrophic effects on device per formance, showing that standard photoprocessing is a viable approach t o fabrication of polymer LED structures. It is anticipated that optimi zation of the procedures will allow much less degradation in device pe rformance, In addition it is shown that photoprocessing can be readily applied to the fabrication of arrays of micron-sized LEDs, demonstrat ing advanced applications of this combination of technologies.