Abstract
The object of this research is to utilize the material, PFCn6, developed in our laboratory as interlayer in multi emitting layer white polymer light emitting diode (MWPLED), to increase its efficiency and to design a new crown ether molecule so that the high work function metal can be used as cathode to increase the life time of device. In 2013, Dr. Yao-Tang Chang of our laboratory has applied the concept of confining the recombination zone effectively, to make the emitting light color independence of electric field. In order to increase the brightness and efficiency of MWPLED, we add green dopant into blue emitting layer and yellow emitting layer. When green dopant is added into the blue emitting layer, we found that the solvent, ethyl acetate, used to form β-PFO and that the mixed solvent of ethyl acetate and methanol, used to facilitate interlayer, PFCn6, will bring way the green dopant during the processing which cause that the green dopant cannot be in blue emitting layer. We introduce the bluish green fluorescent dopant TBPe into the yellow emitting layer. When TBPe and rubrene dopant concentration are 1.0 wt% and 0.5 wt% respectively, we achieve the white light device with green light source which has the maximum brightness 8090 cd/m2, the maximum efficiency 4.45 cd/A, and the CIE coordinate of (0.30,0.38). When rubrene dopant concentration is increased to 2wt%, the efficiency of device is further increased to 7.64 cd/A, and the maximum brightness is 15354 cd/m2. However, the CIE coordinate shifts to (0.38,0.42) and the TBPe characteristic peak disappears. This is because the PL emission peak of TBPe is well overlapped with the UV absorption peak of rubrene, which makes the character switches from green emission to media of energy transport. Furthermore, we optimize the thickness of each layer and adjust rubrene dopant concentration to 1 wt%, the device efficiency is improved to 9.28 cd/A, the maximum brightness is 8015 cd/m2, and the CIE coordinate is (0.33,0.37). This is the highest record on the device efficiency in multi emitting layer white PLED with fluorescent dyes only. On the other hand, when using PFCn6:K+ as electron transport layer the electron injection from aluminum cathode can significantly increase without using air sensitive metal, such as Ca, CsF and LiF …etc, therefore, we attempt to synthesize a new crown ether molecule with aza-crown ether and wish to use the low-cost, stable and high work function metal, copper, as the cathode. The synthesis of aza-crown ether is finished and characterized. Confirming that the product synthesized is correct. We then attach aza-crown ether to the side chain of fluorine, confirming that the product with protected group is correct. However, following up research work was not carried out due to the limitation of time.