Polymer light-emitting diodes (PLEDs) have attracted great attention in recent years due to their potential advantages in fabrication

mechanical properties

and low cost.Balance of charge injection and transporting is a key factor that determines device performances such as efficiency and operating lifetime.Usually

carrier-transporting layer or block layer was inserted into the device to improve the balance of the injected carriers.In this paper

PLEDs with different thickness of luminescent layer were fabricated.The conjugated polymer poly (2-methoxy

5-(2-ethylhexyloxy)-1

4-phenylene vinylene) (MEH-PPV) was used as a luminescent layer.By blending PBDinto the luminescent layer in different concentration

comparing and analysising their properties of Current density-voltage (

J-V

) and Luminance-efficiency-voltage (

L-E-V

)

we found that the PBDnot only enhanced the transporting of the electrons but also blocked the injection of the holes and leading to a better balance of the carriers

which improves the performances of PLEDs.The optimum concentration of the PBDwas found to be 20%.ELemissions of blend devices were red-shifted by about 7 nm from the peak emission at 589 nm of pure MEH-PPVdevice to around 596 nm of devices with the blend film as EML (emission layer).The Full width at half maximum (FWHM) was narrowed from 100 nm to 44 nm.