White Electroluminescence Using Eu-Complexed Copolymer as the Red Unit

Abstract

Europium complexes exhibited intense red fluorescence with a narrow spectral bandwidth. But non-uniform blending or dispersion of complex resulted in phase separation, decomposition and inefficient energy transfer to reduce emission efficiency. The complexes were covalently attached to the main chain of polymers, which improved film quality and solubility. Eu (TTA)2(AA)(TPPO)2 as europium complex monomer (ECM) was prepared by Eu3+ coordinating with triphenylphosphine oxide (TPPO), acrylic acid (AA) and 2-thenoyltrifluoroacetone (TTA). Fluorescent Polymer marked as p1-30 (molar ratio for ECM/N-vinylcarbazole (NVK), 1/30) was synthesized. The emissions of ECM and p1-30 peaked at ca. 610 nm. The highest occupied molecular orbit (HOMO) and the lowest unoccupied molecular orbit (LUMO) energy levels were-5.36 and-1.99 eV. The organic light-emitting devices (OLED) A ITO/PEDOT: PSS/PBD: p1-30/AlQ3/ LiF/Al and B ITO/PEDOT: PSS/PBD: p1-30/BCP/AlQ3/LiF/Al were fabricated. A 4 nm thickness of BCP as a hole-block layer was introduced in Device B to block the movement of holes partly and to reduce the emission from AlQ3. Devices A and B mainly emitted white emission and exhibited luminance of 420 and 315 cd/m2 with Commission International de LEclairage (CIE) coordinates of (0.317, 0.392) and (0.336, 0.380), respectively. The emission from carbazole moieties was suppressed, electroluminescent (EL) spectra revealed that effective intramolecular energy transfer from carbazole unit to europium complex occurred.