Kunping Guo

Flexible electroluminescent fiber fabricated from coaxially wound carbon nanotube sheets

A fiber-shaped polymer light-emitting electrochemical cell (PLEC) was developed by sandwiching an electroluminescent polymer layer between two aligned carbon nanotube (CNT) sheet electrodes. Similar to a conventional planar PLEC, the electroluminescent polymer layer and two carbon nanotube electrodes are closely and stably contacted, so that the injected charges can be rapidly and efficiently transported. Due to their one-dimensional structure, the fiber-shaped PLEC demonstrates unique and promising advantages, e.g., the luminance is almost independent on the observation angle. In addition, the fiber-shaped PLEC is thin, lightweight and flexible, which bespeaks a promising future for various electronic textiles.

Extremely high external quantum efficiency of inverted organic light-emitting diodes with low operation voltage and reduced efficiency roll-off by using sulfide-based double electron injection layers

Inverted organic light-emitting diodes (IOLEDs) have great potential application in flat-panel displays. High energy consumption, efficiency roll-off, and poor electron injection are key issues limiting the use of IOLEDs. Here, we present IOLEDs with extremely low driving voltage, high efficiency and efficiency roll-up by employing double electron injection layers (D-EILs) composed of metal sulfide and cesium carbonate (Cs2CO3)-doped 4,7-diphenyl-1,10-phenanthroline (Bphen). We demonstrate that the use of D-EILs with metal sulfides can significantly improve the performance of IOLEDs. For a blue florescent device based on (2 nm-zinc sulfide)/Bphen: Cs2CO3, we achieve a power efficiency of 10.9 lm W−1 at a luminance of 1000 cd m−2, giving a turn-on voltage of 2.8 V. Notably, the external quantum efficiency increases from 6.9 to 7.5% and the current efficiency increases from 14.3 to 15.4 cd A−1 with the rise in luminance from 1000 to 10 000 cd m−2. Also, the copper sulfide-based device exhibits very-low operating voltages of 4.0 V and 5.3 V at the luminance of 1000 and 10 000 cd m−2, respectively. For a green phosphorescent device, approximately 1.2-fold improvement in external quantum efficiency was obtained compared to the conventional structure. We attributed the improved performance to dipole–dipole interactions at the sulfide-organic interface.

Improved performance of polymer solar cells by using inorganic, organic, and doped cathode buffer layers*

The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) polymer solar cell, we studied the effect of the cathode buffer layer (CBL) between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode (OLED) were employed as the CBL in the P3HT:PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs2CO3, bathophenanthroline (Bphen), and 8-hydroxyquinolatolithium (Liq) can be used as CBL to efficiently improve the device performance of the P3HT:PCBM polymer solar cells. The P3HT:PCBM devices employed various CBLs possess power conversion efficiencies (PCEs) of 3.0%–3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen:Cs2CO3 and Bphen:Liq as the CBL, the PCE of the P3HT:PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL.

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.

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.