Efficient deep-red organic light-emitting diodes based on blending MEH-PPV with a small molecule compound

Efficient deep-red organic light-emitting diodes (OLEDs) were investigated based on the blend of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with 4,7-bis(5-(7-(9H-carbazol-9-yl)-9,9-dioctyl-9H-fluoren-2-yl)thiophen-2-yl)benzo[c] [1,2,5] thiadiazole (compound 1 ). By optimizing the blend ratio, the turn-on voltage of the devices was significantly reduced from 4.9 V to 2.4 V. A highest external quantum efficiency of 2.56% was achieved at a blend ratio of 95:5 (wt) for compound 1 : MEH-PPV. The CIE coordinate was measured to be (0.70, 0.30), with the luminescence peak at around 680 nm. Based on experimental observations the improvement mechanism is described.