Novel electron transporting materials for highly efficient fully solution-processed green PhOLEDs with low rolls-off and drive voltage

• Published in: Dyes and pigments 2018-11, Vol.158, p.20-27
• Main Authors: Wu, Cao, Zhong, Zhi-Ming, Li, Xiang-Gao, Xiao, Yin, Peng, Feng, Wang, Xue, Huang, Zhen-Qiang, Wang, Shi-Rong, Ying, Lei
• Format: Article
• Language: English
• Subjects: Fully solution-processed; High efficiency; High electron mobility; Low drive voltage; Low rolls-off
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2018.05.007

Two novel alcohol-soluble electron transporting materials, diphenyl(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)phosphine oxide (PhOXDPO) and ((1,3-phenylenebis(1,3,4-oxadiazole-5,2-diyl))bis(4,1-phenylene))bis(diphenylphosphine oxide) (Ph2OXDPO), were synthesized and utilized in fully solution-processed green phosphorescent organic light emitting diodes (PhOLEDs). The photo-physical, electrochemical and thermal properties, and electron mobility of PhOXDPO and Ph2OXDPO had been investigated in detail. The photo-physical and electrochemical result showed that the PhOXDPO and Ph2OXDPO had lower highest occupied molecular orbitals (HOMO) level (−6.24 eV and −6.09 eV) and high triplet level (2.79 eV and 2.66 eV). Both PhOXDPO and Ph2OXDPO achieved high electron mobility of 6.6 × 10−4 cm2 v−1 s−1 and 6.0 × 10−4 cm2 v−1 s−1. The current efficiency of the device based on PhOXDPO reached 49.5 cd A−1, and showed only 1.5% roll-off at 1000 cd m−2. Due to the more matchable energy gap and low HOMO level of PhOXDPO, the PhOXDPO based device presented better efficiency than the device with Ph2OXDPO as ETL. Compared with the ETL-free device, the efficiencies of the devices based on PhOXDPO and Ph2OXDPO increased up to one order of magnitude, and remained a high level (38.666 cd A−1 and 37.834 cd A−1, at 10000 cd m−2). The device used TPBI as ETL made by vacuum evaporation and the device ultilized Bphen as ETL made by spin-coating showed much lower efficiency and luminance, on every voltage, than the devices based on PhOXDPO and Ph2OXDPO. [Display omitted] •Two novel alcohol-soluble electron transporting materials had been synthesized and utilized on green PhOLEDs.•The current efficiency of the device based on PhOXDPO reached 49.5 cd A−1, and showed only 1.5% roll-off at 1000 cd m−2.•The efficiencies of the devices based on PhOXDPO and Ph2OXDPO remained high efficiency of 38.666 cd A−1 and 37.834 cd A−1 at 10000 cd m−2.•The electron mobility of PhOXDPO and Ph2OXDPO achieved 6.6 × 10−4 cm2 v−1 s−1 and 6.0 × 10−4 cm2 v−1 s−1.