Enhancing the electroluminescent efficiency of poly{5‐methoxy‐2‐[(2′‐ethyl‐hexyl)‐oxy]‐p‐phenylenevinylene}/poly(2,3‐diphenyl‐5‐octyl‐p‐phenylenevinylene) polyblends by the introduction of chemical bonding through a thermal treatment

Abstract

A significant improvement in the electroluminescence (EL) properties was observed for a poly{5-methoxy-2-[(2 0 -ethyl-hexyl)-oxy]-p-phenylenevinylene} (MEH-PPV)/poly(2,3-diphenyl-5-octyl-p-phenylenevinylene) (DPO-PPV) blend after a thermal treatment at 200 8C for 2 h in vacuo to furnish the chemical bonding between polymer chains. 1 H NMR spectroscopy and two-photon excitation microscopy revealed that the chemical bonding turned the immiscible polyblend into a system more like a block copolymer with a vertically segregated morphology. Because both the lowest unoccupied molecular orbital and highest occupied molecular orbital levels of MEH-PPV in the wetting layer were higher than those of DPO-PPV in the upper layer, the heterojunction between the two layers of the polymers fit the category of so-called type II heterojunctions. As a result, the turn-on voltage of the polymer light-emitting diode prepared with the thermally treated polyblend decreased to $0.6 V, and the EL emission intensities and quantum efficiencies increased to about 4 times those of the untreated polyblend. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 62-69, 2006