Improving the performance of polymer light-emitting diodes using polymer solid solutions

Optical and electronic properties of conjugated polymers can be modified si gnificantly by arranging the polymer chains differently. For example, it is well known that polymer solutions of lower concentrations have different p hotoluminescence spectra from solutions of higher concentrations. In this m anuscript, we demonstrated that such effects can also be achieved in solid states, i.e., in polymer solid solutions consisting of a narrower band-gap material-poly(2-methoxy-5(2'-ethyl-hexyloxy)-1,4-phenylene vinylene (MEH-PP V) with a wider band-gap polymer-poly(9,9-dioctylfluorene). At very low MEH -PPV concentrations, emission spectra of these solid solutions are similar to the photoluminescence spectrum of a diluted MEH-PPV solution in an ordin ary organic solvent, suggesting the absence of a significant amount of inte rchain species. In addition, the electroluminescence efficiency is signific ant enhanced. Furthermore, the full width at half maximum (FWHM) is dramati cally reduced at lower MEH-PPV concentrations, as a result of suppressed in terchain interactions. This approach is particularly important for the appl ication to display technology, in which well-defined narrow FWHM emission s pectra of red, green, and blue colors are required. (C) 2001 American Insti tute of Physics.