Abstract
There are three chapters in this thesis, the chief of chapter 2 focus on electron transporting materials. These molecules were composed of 1, 3, 4-oxadiazole moieties as the electron transporting parts bridging by the m-terphenyl functional groups. We used m-terphenyl group to interrupt the conjugation of the aromatics and maintain a high singlet and triplet energy gap. These six materials have been synthesized and used as ETLs (electron transporting layers) in devices. In the FIrpic (bis(4,6-difluorophenyl-pyridine)(picolinate)iridium(III))-based device using tOXD-mTP (bis(2-tert-butyl-1,3,4-oxadiazole-5-diyl)3,3’-m-terphenyl) as the ETM the highest device performance was achieved, moreover the tpOXD -mTP (bis(2-(4-tert-butylphenyl)-1,3,4-oxadiazole-5-diyl) 3,3’-m-terphenyl) have better thermal properties than others m-terphenyl compounds. Therefore, we selected these two molecules as the ETMs (electron transporting materials) and then used BCPO (bis-(4-(N-carbazolyl)phenyl)phenyl-phosphine oxide) as the host material to fabricate the devices. The best one of FIrpic-based devices reached an EQE of 23%, current efficiency of 43 cd A-1 and CIE of (0.13, 0.29). To use these ETMs for deeper blue phosphorescence device, FIr6 (bis(4’,6’-difluorophenylpyridin -ato)-iridium ( III ) tetra(1-pyrazolyl)borate) based devices showed the external quantum efficiency of 25%, current efficiency of 42 cd A-1,and CIE of (0.14, 0.23). Based on the concept of chapter 2, the azole derivatives have good thermal stability and morphology. The chief of chapter 3 we used the triazole functional group as electron transporting moiety and carbazole group as the hole transporting moiety to construct the host materials. For the devices, using the PO-01 (iridium IV (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2’)acetylacetonate) and Ir(ppy)3 (fac-tris( 2-phenylpyridinato-N,C2’)iridium) as the dopant. The yellow color device exhibited the external quantum efficiency of 20.4%, current efficiency of 78.3 cd A-1, and power efficiency of 70.3 lm W-1. The green color device exhibited the external quantum efficiency of 24.5%, current efficiency of 93.3 cd A-1, and power efficiency of 73.3 lm W-1 at CIE (0.27, 0.65). The operational lifetime of green color device was tested under the luminance of 500 cd m-2. The T50 (50% of initial luminance) was about 1014 hours. The gist of chapter 4 was about developing the host materials applying to blue fluorescence devices through solution processes. The devices using DOPPP (1-(2,5-dimethoxy-4-(1-pyrenyl)phenyl)-pyrene) as the host showed an excellent performance in our previous report. However, the poor solubility of DOPPP made it unable to form organic films by spin-coating method. Here we added alkyl chains to the benzene group of DOPPP to improve its solubility. In the test of light blue devices, device 3I can achieve a high power efficiency of 6 lm W-1. In the case of deep blue device using BCzVBi (4,4’-bis(9-ethyl-3-carbazovinylene)-1,1-biphen -yl) as the dopant, an external quantum efficiency of 3.9%, current efficiency of 4.3 cd A-1, and power efficiency of 2.2 lm W-1 with CIE of (0.14, 0.12) were achieved.