The effects of mixed electroluminescent (EL) polymer layer thickness on the single layer organic light emitting diode (OLED) performance

Single layer OLEDs by using polymer poly(9,9-di-n-hexylfluorenyl-2,7-diyl) (PHF) mixed with organic salt tetrabutylammonium hexafluorophosphate (TBAPF₆) as the electroluminescent (EL) layer were fabricated. This paper reports the effects of variation of that EL layer thickness on the OLED performance. OLEDs performance are determined in terms of their turn-on voltage and luminance. The PHF:TBAPF₆ EL layers with weight ratios of 100:20 were used and prepared by spin coating technique using chloroform as solvent. The thickness being incremented by adding layer-by-layer during the spin coating process. The thickness effects to the EL layer surface roughness were also studied. The best device performance was given by the thinnest layer which also has the lowest average surface roughness (0.557 nm), it gave the lowest turn-on voltage (7.0 V) and highest maximum luminance (9.12 cd/m² at 10 V). It emitted greenish-yellow color at it maximum luminance with CIE coordinate (0.30, 0.55).