Highly Improved Quantum Efficiency in Blend Polymer LEDs

Abstract

We report on light-emitting diodes (LEDs) made from blend polymers composed of two organic soluble and emittable conducting polymers, poly[2-methoxy-5-(2-ethylhexyloxy-1,4-phenylenevinylene] (MEH-PPV) and poly[1,3-propanedioxy-1,4-phenylene-1,2-ethenylene(2,5-bis(trimethylsilyl)-1,4-phenylene)-1,2-ethenylene-1,4-phenylene] (DSiPV), as the emitting layers. The emitting colors of the blend polymers were yellowish orange, which indicates that the emission is mainly due to MEH-PPV and DSiPV greatly contributes to the enhancement of the luminescence. The efficiencies of the blend polymers increase with decreasing MEH-PPV/DSiPV weight ratio. In blending MEH-PPV with DSiPV, DSiPV is believed to serve as an EL enhancing polymer rather than EL active in our devices. The quantum efficiency is measured as the function of MEH-PPV content in the blend. Especially, the maximum quantum efficiency of MEH-PPV/DSiPV(1/15) blend polymer is about 500 times greater than that of MEH-PPV homopolymer, and the luminance is up to 500 cd/m2 at 30 V with 23.6 mA/cm2 current density.