Yaoqi Li

Multilayered graphene used as anode of organic light emitting devices

In this report, we find multilayered graphene, which has good transparency, conductivity and suitable work function, can be used as the anode for the organic light emitting device. Our device structure is Al/glass/multilayered graphene/V2O5/NPB/CBP:(ppy)2Ir(acac)/Bphen/Bphen:Cs2CO3/Sm/Au. The maximum luminance efficiency and maximum power efficiency reach 0.75 cd/A and 0.38 lm/W, respectively. We believe that by optimizing the hole density and uniforming the thickness of the multilayered graphene anode, the device efficiency can be remarkably increased in the future.

Promoted H2 Generation from NH3BH3 Thermal Dehydrogenation Catalyzed by Metal–Organic Framework Based Catalysts

The application of ammonium borane (AB) as a hydrogen storage material is limited by the sluggish kinetics of H(2) release. Two catalysts based on metal-organic frameworks (MOFs) have been prepared either by applying MOF as precursors or by the in situ reduction method. In the release of H(2) from AB, the high H(2) content of the whole system, the remarkably lower reaction onset temperature, the significantly increased H(2) release rates at ≤90°C, and the decreased reaction exothermicity have all been achieved with only 1.0 mol% MOF-based catalyst. Moreover, the clear catalytic diversity of three catalysts has been observed and discussed. The in situ synthesized Ni(0) sites and the MOF supports in the catalysts were proven to show significant and different effects to promote the catalytic activities. With MOF-based catalysts, both the enhanced kinetics and the high H(2) capacity of the AB system present great advantages for future use.

Two pillared-layer metal–organic frameworks constructed with Co(II), 1,2,4,5-benzenetetracarboxylate, and 4,4′-bipyridine: syntheses, crystal structures, and gas adsorption properties

Two new metal–organic frameworks (MOFs) [Co2(btec)(bipy)2(DMF)]·DMF·3H2O (1) (btec = 1,2,4,5-benzenetetracarboxylate; bipy = 4,4′-bipyridine; DMF = N,N′-dimethylformamide) and Co2(btec)(bipy)(DMF)2 (2) were synthesized with the same starting materials under different solvothermal conditions. The higher temperature favors the generation of compound 2, while the slightly lower temperature with the higher bipy ratio leads to the porous structure of compound 1. Their structures are determined by single-crystal X-ray diffractions. Compound 1 is a 3D pillared-layer framework with interconnected channels along two directions after the removal of free guest molecules. The BET (Brunauer–Emmett–Teller) surface area of 1 was calculated to be 596 m2 g−1 by nitrogen adsorption at 77 K. The hydrogen adsorption isotherm at 77 K shows an excess uptake of 1.1 wt% at 15 bar. The heat (Qst) of hydrogen adsorption was estimated to be 7.3 kJ mol−1 at zero coverage. In compound 2, the wave-like layers constructed with btec are further pillared by bipy, giving rise to the 3D framework with the 1D channels occupied by coordinated DMF molecules.

Superior hydrogen desorption kinetics of Mg(NH2)2 hollow nanospheres mixed with MgH2 nanoparticles

Mg3N2 nanocubes were prepared by vaporized bulk magnesium in ammonia atmosphere associated with plasma metal reaction. Then the product transformed to Mg(NH2)2 hollow nanospheres after it was reacted with NH3 based on the Kirkendall effect. The electron microscopy results suggested that the obtained hollow nanospheres were around 100nm and the shell thickness was about 10nm. Because of its short distance for Mg2+ diffusion and large specific surface area for interaction between Mg(NH2)2 and MgH2, the structure dramatically enhanced the hydrogen desorption kinetics of Mg(NH2)2–2MgH2.

Top-emission Si-based phosphor organic light emitting diode with Au doped ultrathin n-Si film anode and bottom Al mirror

We report a highly efficient top-emission Si-based phosphor organic light emitting diode (PhOLED) with an ultrathin polycrystalline n-Si:Au film anode and a bottom Al mirror. This anode is formed by magnetron sputtering followed by Ni induced crystallization and then Au diffusion. By optimizing the thickness of the n-Si:Au film anode, the Au diffusion temperature, and the other parameters of the PhOLED, the highest current and power efficiencies of the n-Si:Au film anode PhOLED reached 85±9 cd/A and 80±8 lm/W, respectively, corresponding to an external quantum efficiency of 21±2% and a power conversion efficiency of 15±2%, respectively, which are about 60% and 110% higher than those of the indium tin oxide anode counterpart and 70% and 50% higher than those of the bulk n+-Si:Au anode counterpart, respectively.

Au generation centres doped n+-Si: hole-injection adjustable anode for efficient organic light emission

An organic light-emitting diode (OLED) with an n-Si-anode usually has an efficiency evidently lower than the OLED with the same structure with a p-Si-anode due to insufficient hole injection from the n-Si anode compared with the p-Si-anode. In this study, we find that introducing Au as generation centres with a suitable concentration into the n+-Si anode can enhance hole injection to match electron injection and then considerably promote the power efficiency. With optimizing Au generation centre concentration in the n+-Si anode, the OLED with a structure of n+-Si: Au/NPB/AlQ/Sm/Au reaches a highest power efficiency of 1.0 lm W−1, evidently higher than the reported highest power efficiency of 0.2 lm W−1 for its p-Si-anode counterpart. Furthermore, when the electron injection is enhanced by adopting BPhen:Cs2CO3 partly instead of AlQ as the electron transport material, and the Au generation centre concentration in the n+-Si anode is promoted correspondingly, then a highest power efficiency of 1.8 lm W−1 is reached. The role of Au generation centres in the n+-Si anode is discussed.