Changfeng Si

Iridium(III) complexes bearing oxadiazol-substituted amide ligands: color tuning and application in highly efficient phosphorescent organic light-emitting diodes

By adjusting the conjugation degrees of the phenylquinoline-based cyclometalated ligands, yellow, orange to red phosphorescent iridium(III) complexes [Ir(bzq)2(POXD)] (1, bzq = 7,8-benzoquinoline, POXD = N-(5-phenyl-1,3,4-oxadiazol-2-yl)-diphenylphosphinic amide), [Ir(pq)2(POXD)] (2, pq = 2-phenylquinoline) and [Ir(piq)2(POXD)] (3, piq = 1-phenylisoquinoline) have been designed and prepared. Their photophysical and electrochemical studies and theoretical calculations were performed, and [Ir(bzq)2(POXD)] was also determined by X-ray crystallography. At room temperature, complexes 1–3 exhibit efficient phosphorescence emissions at about 539, 592 and 614 nm with photoluminescence quantum yields (PLQYs) of 0.21, 0.06 and 0.06 in CH3CN solutions, respectively. In the 5 wt% doped poly(methyl methacrylate) (PMMA) film, the PLQYs (0.35 for complex 1, 0.37 for complex 2 and 0.18 for complex 3, respectively) increase significantly. Organic light emitting diodes (OLEDs) based on these complexes were fabricated to evaluate their potential application. The yellow device in the configuration ITO/2-TNATA (25 nm)/NPB (5 nm)/TCTA (10 nm)/complex 1 (10 wt%):mCP (10 nm)/complex 1 (10 wt%):TPBi (10 nm)/TPBi (40 nm)/Liq (1 nm)/Al (100 nm) shows excellent performance with a maximum luminance of 24 080 cd m−2, maximum current efficiencies of 70.1 cd A−1 and maximum external quantum efficiencies of 21.3% along with low efficiency roll-off.

Low-energy consumption and high-color-quality white organic light-emitting diodes

White organic light-emitting diodes (WOLEDs) offer a range of attractive characteristics include easily processable, glare-free and generate light over a large area. However, high-energy consumption, unreliable and low-color-quality are key issues limiting the future of WOLEDs. Enormous efforts in chemistry and the materials sciences to design better materials as well as in physics and engineering to invent new device concepts and design suitable fabrication schemes have been endeavored. This article reviews current developments in the field of WOLEDs and puts a special focus on new device concepts and on approaches to low-energy consumption and high-color-quality WOLED manufacturing.

Efficiency enhancement in DIBSQ:PC71BM organic photovoltaic cells by using Liq-doped Bphen as a cathode buffer layer

We have improved the photovoltaic performance of 2,4-bis[4-(N,Ndiisobutylamino)- 2,6-dihydroxyphenyl] squaraine:[6,6]-phenyl C71-butyric acid methyl ester (DIBSQ:PC71BM) organic photovoltaic (OPV) cells via incorporating Liq-doped Bphen (Bphen-Liq) as a cathode buffer layer (CBL). Based on the Bphen-Liq CBL, a DIBSQ:PC71BM OPV cell possessed an optimal power conversion efficiency of 4.90%, which was 13% and 60% higher than those of the devices with neat Bphen as CBL and without CBL, respectively. The enhancement of the device performance could be attributed to the enhanced electron mobility and improved electrode/active layer contact and thus the improved photocurrent extraction by incorporating the Bphen-Liq CBL. Light-intensity dependent device performance analysis indicates that the incorporating of the Bphen-Liq CBL can remarkably improve the charge transport of the DIBSQ:PC71BM OPV cell and thus decrease the recombination losses of the device, resulting in enhanced device performance. Our finding indicates that the doped Bphen-Liq CBL has great potential for high-performance solution-processed small-molecule OPVs.

Ultrahigh-luminance organic light-emitting diodes using LiF/MgAg as cathode for the application of both surface emission

ABSTRACT The effect of different species of cathode on the performance of organic light-emitting diodes under direct current drive has been investigated in this paper. The organic light-emitting diode using LiF/Al and LiF/MgAg layer as cathode has been fabricated, and the luminance of device with cathode structure of LiF/MgAg was found to realize higher efficiency. The performance of the device was found to be improved greatly due to efficient electron injection from MgAg cathode. Moreover, a configuration of LiF/MgAg/IZO (indium zinc oxide) was developed, finding that both the top-emitting intensity and the bottom-emitting intensity achieve very-high luminance, and in this basis, transparent OLEDs with the extremely high-luminance of about 100,000 cd/m2 has been realized, which is considered as the highest luminance among the previous works.

Enhanced performance in inverted organic light-emitting diodes using Li ion doped ZnO cathode buffer layer

ABSTRACT Inverted organic light-emitting diodes (IOLEDs) have great potential application in flat-panel display. In this study, a lithium (Li) ion doped solution processed zinc oxide (Li-ZnO) layer was employed as the cathode buffer layer (CBL) for IOLEDs. The Li-ZnO CBL was prepared by inducing the Li ion of 8-hydroxyquinolatolithium (Liq) to diffuse into ZnO film through thermal annealing the bi-layer ZnO/Liq film. Based on the Li-ZnO CBL with ultraviolet(UV) treatment, the IOLED using tris(8-hydroxyquinoline) aluminum as the emitting layer possessed an optimal current efficiency of 4.42 cd A−1, which was improved by 55% than those of the devices with neat ZnO as CBL. The enhancement of the device performance could be attributed to the enhanced electron mobility and electron injection ability of the Li-ZnO CBL. Our finding indicates that the low-temperature deposited Li-ZnO film has great potential for the application of OLED display.