Carrier transport and improved emission properties of bilayer polymer light-emitting transistors based on crystalized poly(alkylfluorene) films

Abstract

In order to clarify the carrier transport and improve the emission characteristics of polymer light-emitting transistors, the fabrication and properties of top-gated bilayer polymer light-emitting transistors with oriented poly(9,9-dioctylfluorene) (F8) films and a phosphorescent dye doped in F8 are investigated. For bilayer devices with different oriented F8 films, both the hole and electron mobilities of bilayer devices are dependent on those of F8 upper layer. The bilayer devices using an oriented F8 upper layer with the channel direction parallel to the polymer orientation exhibit higher hole and electron mobilities, and improved EL intensity than those with the channel direction perpendicular to the polymer chains orientation. Devices with a phosphorescent dye-doped layer also exhibit the ambipolar and light-emitting properties. Both fluorescence and phosphorescence emissions can be achieved for bilayer devices. We demonstrate the possibility of improved emission for bilayer devices using a conjugated polymer doped with a phosphorescent material as the upper layer.