Chuannan Li

White light emission induced by confinement in organic multiheterostructures

A technique for inducing white-light emission from organic multiheterostructures is proposed. The configuration of organic multiheterostructure white-light emitting diodes is ITO/TPD(50 nm)/BePP2(5 nm)/TPD(4 nm)/BePP2:rubrene(5 nm)/TPD(4 nm)/Alq3(10 nm)/Al. Triphenyldiamine derivative (TPD) is used as a hole-transporting layer and the potential barrier layers. Blue fluorescent phenylpyridine beryllium (BePP2), orange fluorescent rubrene, and green fluorescent aluminum complex (Alq3) are used as three primary colors. BePP2 and BePP2 doped with rubrene act as the potential wells sandwiched between TPD barrier layers, in which excitons are confined. Alq3 is used as an electron-transporting green-color emitter. The white-light emission spectrum covers a wide range of the visible region, and the Commission Internationale de l’Eclairage coordinates of the emitted light are (0.32, 0.38) at 9 V. The maximum brightness and luminous efficiency of this device are 4000 cd/m2 (at 17 V) and 0.4 lm/W, respectively.

Highly efficient phosphorescent organic light-emitting devices based on Re (CO )3Cl -bathophenanthroline

Highly efficient orange organic electroluminescent devices based on Re(CO)3Cl-bathophenanthroline have been fabricated. A device with 9 wt% shows the highest efficiencies of 13.8 cd A−1 (luminance efficiency), 8.69 lm W−1 (power efficiency) and 5.24% (external quantum efficiency). Maximum luminance over 4000 cd m−2 is obtained. By discussing the mechanisms, it is believed that trapping contributes mostly to these relatively much higher efficiencies.

Electronic structure of cubic Li(Fe0.1Mn1.9)O4 studied with Mössbauer spectroscopy and first-principles calculation

Mossbauer spectrum was collected in Fe3+ doped cubic LiMn2O4 (LiFe0.1Mn1.9O4) by using 57Fe as the radiation source. In the model of the crystal-field theory, the energy gaps between different d orbitals, ΔE(b1g−a1g) and ΔE(b2g−eg), characterize the strength of the Jahn–Teller effect in the crystal. A relationship between the Mossbauer quardrupole splitting and the energy gaps was established, based on which both ΔE(b1g−a1g) and ΔE(b2g−eg) of the [MnO6] octahedron in LiFe0.1Mn1.9O4 are estimated to be about 0.41 and 0.30 eV, respectively. Electronic structure of LiMn2O4 was studied theoretically via ab initio calculation based on the density-functional theory. Calculation shows that a gap about 0.28 eV between the filled Mn d bands is equivalent to ΔE(b2g−eg). It also shows that the first unoccupied states are dominated by Mn 3d contribution essentially from both a1g and b1g of Mn d states. Distance between the two peaks in the first unoccupied band was used to calculate ΔE(b1g−a1g), which is about 0.36 e...

HIGH EFFICIENT GREEN EMISSION FROM ORGANIC MULTI-QUANTUM WELLS STRUCTURE

Organic green light emitting devices (LEDs) with multi-quantum wells (MQWs) structure were fabricated. Aromatic diamine was used as hole-transporting layer and potential barrier layer; tris (8-hydroxyquinoline) aluminum acted as electron transporting layer and MQWs green emitting layer. The influence of the barrier layer thickness and quantum well number to the device performance was also investigated. The barrier thickness must be thin (such as 4 nm) enough to tunnel through and distribute charge carriers uniformly in different wells (mainly electrons). The organic MQWs LEDs showed enhanced electroluminescent efficiencies. Maximum luminous efficiency and external quantum efficiency were 1.24 lm/W and 1.04%, respectively.

A high performance fluorescent white organic light-emitting device and its optimization for full-colour display

A white organic light emitting diode (OLED) was fabricated in which blue emission host 9,10-di(2-naphthyl)anthracene (ADN) doped with an orange emission dye (rubrene) was used to generate bright, high efficiency white light. A large amount of work was done to study the emission mechanism of a rubrene-doped device. Finally, to get optimized EL spectra, we introduced a green light which is emitted from tris(8-hydroxy-quinoline) aluminium (Alq3), the electron transport material, into the emission of white light.

Highly efficient and bright doped organic electroluminescent diodes using an aluminum electrode

Remarkable improvement in efficiency and electroluminescence (EL) has been observed in an organic EL device, which consists of a hole-transport layer and a luminescent layer. The hole-transport layer is an N,N′-bis(3-methyphenyl)-N,N′-diphenylbenzidine film. The doped emitting layer consists of 8-(quinolinolate)-aluminum as the host and rubrene as the emission dopant. The doped cell with aluminum cathode demonstrated a luminance in excess of 20,000 cd/m2 and an external quantum efficiency of 2.7%, which is about four times and three times, respectively, greater than those of the undoped cell. The EL emission from the device shows spectral narrowing and a shift to higher energy.

Organic single-quantum-well electroluminescent device

A new kind of single-quantum-well electroluminescent (EL) device consists of a hole transport N,N-Bis(3-methyphenyl)-N,N-diphenylbenzidine(TPD) layer, and electron transport 8-(quinolinolate)-aluminum(Alq) layer and a light emitting layer of Alq doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) has been fabricated by the multisource-type high-vaccum organic molecular deposition. The dopant rubrene is as a potential well, and the undoped Alq layer is as a barrier layer. The EL spectra shows the spectral narrowing and the emission peak energy blue-shift, and the efficiency and luminance of the device have been significantly improved. The experimental phenomena is explained as the result of recombination of carriers from the quantized energy state.