High-efficiency inverted top-emitting polymer light-emitting diodes

A major challenge to inverted top-emitting polymer light-emitting diodes (ITEPLEDs) is to prepare a reflective bottom cathode capable of effectively injecting electrons. Reported in this letter is the creation of an efficient electron injection layer (EIL) by using environment-friendly alcohol-/water-soluble aminoalkyl-substituted conjugated quanternized polyfluorene copolymers containing 0.5%mol of benzothiadiazole to reduce the electron injection barrier between the high-work-function Al reflective bottom cathode and the light-emitting layer. The inverted top-emitting devices exhibit superior electrical characteristics with maximal quantum and luminance efficiencies of 2.71% and 1.6cd∕A respectively, at an operating voltage of 13.3V by employing poly[2-methoxy,5-(2-ethylhexyloxy)-1,4-phenylenevinylene] as a light-emitting polymer. The utilization of water/alcohol soluble conjugated polyelectrolyte/Al bilayer bottom cathode offers an important advantage for avoiding intermixing between the emitting layer and the EIL for solution-processable ITEPLEDs.