Hole blocking in carbon nanotube-polymer composite organic light-emitting diodes based on poly (m-phenylene vinylene-co-2,5-dioctoxy-p-phenylene vinylene)

In order to investigate the role of carbon nanotubes in a polymer matrix, o rganic light-emitting diodes were fabricated from a polymer composite compo sed of poly (m-phenylene vinylene-co-2,5-dioctoxy-p-phenylene) (PmPV) and d ispersed single-wall carbon nanotubes (SWNTs). Tris-(8-hydroxyquinolinolato ) aluminum (Alq(3)) doped by Nile Red was used as an emissive material betw een the polymer composite and cathode. The device fabricated without SWNTs dispersed in the PmPV shows a dominant emission near red at 600 nm, which i s in the range of the characteristic emission of Nile Red-doped Alq(3), wit h a small amount of green emission from the PmPV. However, the devices fabr icated with the polymer composite show an increase in the oscillator streng th of the green emission with a dominant emission peak near 500 nm, the cha racteristic emission of PmPV. This was observed for SWNT concentrations up to 0.1 wt %. The shift in the emission indicates that the SWNTs in the PmPV matrix act as a hole-blocking material that results in a shifting of the r ecombination region from the Nile Red-doped Alq(3) layer to the PmPV compos ite layer. (C) 2000 American Institute of Physics. [S0003-6951(00)05135-4].