White light emitting diode based on quantum dots and MEH-PPV

The white light emitting diode (LED) devices, in which blue-emitting quantum dots doped in the polymer of poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylene vinylene] (MEH-PPV) serve as the active layer, have been fabricated in a nitrogen-filled glove box; the devices have the structure of ITO/PEDOT/MEH-PPV:QDs(B)/LiF/Al. After a systematical investigation, we report the effect of different quantum dots (QDs) doping concentration (mass fraction) on the electroluminescent spectrum, current density, brightness, CIE coordinates of the devices and atomic force microscopy (AFM) characterizations of the emitting layer. With the increase of QDs doping concentration, we find that the QDs luminance intensity of the controlling devices continues to grow. When the QDs doping concentration is 40%, the normal white light emission is obtained in the devices. The CIE coordinates of the white QD-LED are (0.35, 0.32), which are close to the balanced white coordinates. Besides, we also fabricate the non-doped devices, in which the structure is ITO/PEDOT/MEH-PPV/QDs(B)/LiF/Al. After finishing the active layer's preparation, the morphology of the films are investigated by AFM. By comparing the analysis, the doped system has a lower level on the root mean squared roughness. In addition, the doped devices demonstrate a superior performance, and exhibit a low turn-on voltage and a high maximum value of luminance.