Yongming Yin

Iridium(III) complexes adopting 1,2-diphenyl-1H-benzoimidazole ligands for highly efficient organic light-emitting diodes with low efficiency roll-off and non-doped feature

Two novel iridium(III) complexes (pbi)2Ir(mtpy) (1) and (pbi)2Ir(pbim) (2) adopting 1,2-diphenyl-1H-benzoimidazole (Hpbi) as cyclometalated ligands were successfully synthesized and characterized. Strong emissions at 501 and 536 nm with high photoluminescence quantum yields of 48% and 91% in CH2Cl2 at 298 K were obtained for 1 and 2, respectively. The quantum chemical calculations and the photophysical properties indicated that the dominant 3MLCT (metal-to-ligand charge-transfer) state mixed with 3LLCT (ligand-to-ligand charge-transfer) and 3LC (ligand-centered 3π–π*) characters contributed to their phosphorescence emissions. Doped organic light-emitting diodes (OLEDs) based on 1 and 2 showed a peak current efficiency of 45.0 cd A−1 and power efficiency of 47.9 lm W−1 accompanied by very low efficiency roll-off values. In their non-doped OLEDs, high efficiencies of 24.4 cd A−1 and 26.3 lm W−1 were achieved as well. These appealing results reveal that complexes 1 and 2 open interesting perspectives for the development of high-performance OLEDs in the future.

Efficient non-doped phosphorescent orange, blue and white organic light-emitting devices

Efficient phosphorescent orange, blue and white organic light-emitting devices (OLEDs) with non-doped emissive layers were successfully fabricated. Conventional blue phosphorescent emitters bis [4,6-di-fluorophenyl]-pyridinato-N,C2′] picolinate (Firpic) and Bis(2,4-difluorophenylpyridinato) (Fir6) were adopted to fabricate non-doped blue OLEDs, which exhibited maximum current efficiency of 7.6 and 4.6 cd/A for Firpic and Fir6 based devices, respectively. Non-doped orange OLED was fabricated utilizing the newly reported phosphorescent material iridium (III) (pbi)2Ir(biq), of which manifested maximum current and power efficiency of 8.2 cd/A and 7.8 lm/W. The non-doped white OLEDs were achieved by simply combining Firpic or Fir6 with a 2-nm (pbi)2Ir(biq). The maximum current and power efficiency of the Firpic and (pbi)2Ir(biq) based white OLED were 14.8 cd/A and 17.9 lm/W.

High-efficiency and low-efficiency-roll-off single-layer white organic light-emitting devices with a bipolar transport host

High-efficiency single-layer (SL) white organic light-emitting devices (WOLEDs) with a bipolar transport host were fabricated. The SL WOLEDs were achieved by combining blue and orange emission. Compared with the corresponding multilayer WOLEDs, the SL WOLEDs alleviated the efficiency roll-off without compromise of current efficiency due to the broader exciton formation zone and balance of carrier injection and transport. For example, The power efficiency of the SL WOLED based on Iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2′) acetylacetonate orange emission could reach 20.9 lm/W at 1000 cd/m2, which also could reach 14.5 lm/W at a very high brightness of 5000 cd/m2.

Silver/germanium/silver: an effective transparent electrode for flexible organic light-emitting devices

Mechanical resilience is important for future organic light-emitting devices (OLEDs) in lighting and displays. A key constraint is the electrode used in OLEDs. Here we demonstrate ultra-thin silver/germanium/silver (AGA)-based flexible organic light-emitting devices, with comparable efficiency to their ITO-based counterparts. The fabrication process of AGA electrodes is compatible with that of the OLEDs, and they show excellent optical, electrical and mechanical properties. They can be used as transparent cathodes and anodes for top-emitting, bottom-emitting and transparent flexible OLEDs.

An efficient flexible white organic light-emitting device with a screen-printed conducting polymer anode

A screen-printed poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) layer was used as the anode for a flexible white organic light-emitting device (FWOLED). After 700 bending cycles, the sheet resistance of the anode was increased to 1.8 times the initial value (296 Ω/). The average transmission of the PEDOT : PSS layer on the PET substrate was 74% in the visible light region. At a brightness of 1000 cd m−2, the current and power efficiency of the FWOLED were 26.4 cd A−1 and 10.8 lm W−1, respectively. And after 100 outer bending cycles, the device also had a power efficiency of 5.0 lm W−1 at 1000 cd m−2.

Efficient inverted organic light-emitting devices with self or intentionally Ag-doped interlayer modified cathode

Green phosphorescent inverted organic light-emitting devices (IOLEDs) with self or intentionally Ag-doped interlayer modified cathode were demonstrated. The IOLEDs show low driving voltage and high efficiency. For example, the efficiency of inverted bottom-emitting OLED with ITO cathode is comparable with the conventional bottom-emitting OLED with ITO anode. The top-emitting IOLED with Ag cathode shows high current efficiency of 76.4 cd/A which is 2.38 times of that of the conventional bottom-emitting OLED with ITO anode. The results indicate that the electron injection from cathode was observably improved by the Ag-doped interlayer and such interlayer is cathode independent relatively.

Influence of Thickness on Performance of Blue Single-Layer Organic Light-Emitting Device

Single-layer (SL) blue organic light-emitting devices (BOLEDs) with a bipolar transport host were fabricated. The effects of the active layer thickness on the color purity, efficiency, and efficiency roll-off were investigated. An SL BOLED with 70 nm active layer showed good color purity, high efficiency, and extremely low efficiency roll-off. The power efficiency at 1000 cd/cm2 of the device was 13.1 lm/W. From the brightness at maximum external quantum efficiency to high brightness of 5000 cd/m2, the efficiency roll-off was 11.8%. The excellent performance could be attributed to the broader exciton formation zone and balance of charge carrier injection and transport.

Angle-stable RGBW top-emitting organic light-emitting devices with Ag/Ge/Ag cathode

Ag/Ge/Ag (AGA) is investigated as a transparent cathode for top-emitting organic light-emitting devices (TEOLEDs). TEOLEDs of different colors with excellent performances can be gained by simply adopting a corresponding emitting layer, without changing the thickness of the device and cathode. Especially, the blue and white TEOLEDs exhibit high efficiency as well as the bottom OLEDs and show an excellently angle-stable characteristic. The white TEOLED exhibits a maximum current efficiency of 12.4 cd/A, and the CIE coordinates at 6 V only shift by (0.048, 0.046) from 0° to 60°. It can be attributed to the less angle-dependent cavity emission of the TEOLED with AGA cathode.

Efficient and low-voltage phosphorescent organic light-emitting devices based on blue iridium complex host

By adopting a phosphorescent host/guest system consisting of blue iridium complex as host and a series of phosphorescent dyes as guest, efficient and low-voltage monochromic organic light-emitting devices(OLEDs) were fabricated. The devices with blue iridium host have higher power efficiency than the device with the conventional host 4,4′-N,N′-dicarbazole-biphenyl. The enhancement of the maximum power efficiency in green phosphorescent device can reach 37.2%. Dichromatic white OLED could be achieved by simply adjusting the concentration of the orange dyes. At a brightness of 1000 cd/m2, the power efficiency of the white device is 8.4 lm/W with a color rendering index of 76.