Electroluminescence properties of poly[2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene]/tris(8-hydroxyquinoline) aluminum two-layer devices

Two-layer electroluminescing (EL) devices were constructed employing poly[2 -(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) and tris(8-h ydroxyquinoline)aluminum (Alq(3)). On the indium-tin oxide (ITO) glass anod e MEH-PPV layer was first spin-coated, on which the Alq(3) layer and the al uminum (Al) anode were vapor-deposited sequentially. When the thickness of Alq(3) was less than that of MEH-PPV, the device showed the EL emission spe ctrum originated only from the latter. The devices, however, exhibited the combined EL spectra of MEH-PPV and Alq(3) when latter's layer was thicker t han the former's layer. The external efficiency for light emission by the d ouble-layer devices was improved by close to two orders of magnitude when c ompared with efficiency of the MEH-PPV single-layer device, when the thickn ess of the Alq(3) layer was slightly thicker than that of the MEH-PPV layer . The maximum efficiency obtained was about 0.02%. Current flow in the two- layer devices was limited effectively by the Alq(3) layer and it decreased steadily as the thickness of the Alq(3) layer was increased. The results we re discussed on the basis of improved exciton formation resulting from acce lerated and balanced carrier transport. (C) 2000 Elsevier Science S.A. All rights reserved.