Synthesis and Characterization of Materials for Blue Organic Light-Emitting Diodes
Date Issued
2014
Date
2014
Author(s)
Wu, Cheng-Lung
Abstract
My doctoral dissertation can be divided into three parts. The first and the second parts were focused on designing and synthesizing host materials for the application of blue phosphorescence organic light-emitting diodes. The third part was focused on developing of blue fluorescence light-emitting materials. In the first part, I designed a series of heteroatom-bridged bis-(9,9’-spirobifluorene) derivatives as the host materials. The bridged atoms can maintain the high triplet state energy gap of 9,9’-spirobifluorene via disconnecting π-conjugated systems. The materials were fabricated in the application of blue phosphorescence organic light-emitting diodes. SP2PO and SP2SO2 OLEDs exhibited the best external quantum efficiency of 6.0 and 6.1 %, respectively. In the second part, I attempt to design bipolar host materials based on 9,9’-spirobluorene structure. I successfully synthesized unsymmetric two- or three- substituent 9,9’-spirobilfuorene via modifying the synthesis strategy of 2-iodo-9,9’-spirobifluorene. The hole and electron mobility of host materials can be adjusted by different number of substituents. The materials I synthesized were made into devices for blue phosphorescence organic light-emitting diodes. CzdSPPO and CzdSP2PO OLEDs exhibited the best external quantum efficiency of 11.4 and 11.5 %, respectively. In the final part, I designed and synthesized a new series of 9,10-diphenylanthracene (DPA)-based blue fluorophores. These fluorophores have bulky substituent on C-2 position, such as triphenylsilane of TPSDPA and mesitylene of TMPDPA. C-2 substituent also includes electron transport diphenylphosphine oxide of PPODPA and dimesitylene borane of BMTDPA, or hole transport of N-phenylnaphthalen-1-amine of NPADPA. According to the emission wavelength in solution and the performance of quantum yields of these fluorophores, I selected TMPDPA as model compound for further modification. For TMPDPA blue fluorophores, 9,10-diphenyl substituents of the anthracene core were attached with hole-transporting 9H-carbazole (CBZDPA) and electron-transporting 2-phenyl-1,3,4-oxadiazole (OXDDPA) on para- and meta-position, respectively. These DPA-based fluorophores were fabricated as light-emitting materials in non-dopant blue fluorescent devices. Except of PPODPA, electroluminescence efficiency of these DPA derivatives was all found significantly improved. Particularly, CBZDPA and OXDDPA OLEDs exhibited the best external quantum efficiency of 4.5 and 4.0 % with true blue colour, CIEx,y (0.17, 0.17) and CIEx,y (0.16, 0.18), respectively. Improved electroluminescence efficiency can be attributed to the molecular charge transport design of CBZDPA and OXDDPA.
Subjects
Host Materials
Blue Fluorescent Materials
Organic Light-Emitting Diodes
Type
thesis
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