High-efficiency light-emitting diodes using neutral surfactants and aluminum cathode

High-efficiency polymer light-emitting diodes were fabricated by spin-coating a layer of neutral surfactant on top of the poly[2-methoxy-5- (2′ -ethylhexyloxy)-1,4-phenylenevinylene] electroluminescent (EL) layer to facilitate the electron injection through the high-work-function aluminum cathode. The external luminous efficiency of the device can reach 3.59 cd/A, which is higher than the control device (1.89 cd/A) using calcium as cathode. It was found that when the combination of surfactant and aluminum was used as cathode the abundant hole-injection through a hole-transporting layer and hole pile-up at the inner side of the EL/surfactant interface causes an effective electric field to enhance electron injection. © 2005 American Institute of Physics.