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 transport but also reduce the luminescence quantum yield, leading to a fundamental trade-off in optimizing film morphology for device performance. We present two methods to improve the efficiency of light-emitting diodes (LEDs) based on poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) by altering film morphology without changing device architecture. First, "trilayer" LEDs, which use a central MEH-PPV layer with reduced interchain interactions between layers of highly aggregated MEH-PPV near the electrodes, have a higher efficiency than single-layer devices. Second, device efficiency can be improved by annealing MEH-PPV films, so that the reduced emission upon increasing interchain interactions is overcome by more balanced charge injection. (C) 2000 American Institute of Physics. [S0003-6951(00)03817-1].