Improving the performance of conjugated polymer-based devices by control of interchain interactions and polymer film morphology

Interchain interactions in conjugated polymer films promote good carrier tr ansport but also reduce the luminescence quantum yield, leading to a fundam ental trade-off in optimizing film morphology for device performance. We pr esent two methods to improve the efficiency of light-emitting diodes (LEDs) based on poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-P PV) by altering film morphology without changing device architecture. First , "trilayer" LEDs, which use a central MEH-PPV layer with reduced interchai n interactions between layers of highly aggregated MEH-PPV near the electro des, have a higher efficiency than single-layer devices. Second, device eff iciency can be improved by annealing MEH-PPV films, so that the reduced emi ssion upon increasing interchain interactions is overcome by more balanced charge injection. (C) 2000 American Institute of Physics. [S0003-6951(00)03 817-1].