Structures, Mobilities, and Electronic Properties of Functionalized Silicene: Superhalogen BO2 Adsorption.

The narrow band gap of silicene severely hinders its application in nanoelectronic devices. Therefore, it is significant to open the band gap of silicene and maintain its high carrier mobility. And for that, the adsorption of different coverage superhalogens BO2 on the silicene surface have been investigated based on density functional theory and the CALYPSO method. The results show that BO2 unit prefers to adsorb on silicene with adjacent mode irrespective of the size of substrate. The electronic structure analysis indicates that the density of states near the Fermi level are mainly contributed by Si-p and BO2-p orbitals. (BO2)n-silicene exhibits metallic character with the exception of (BO2)2 adsorbed on 4 × 4 supercell. As for (BO2)2-silicene, silicene transforms from a gapless direct semiconductor to an indirect semiconductor. Furthermore, the effective electron mass of two BO2 superhalogens on 4 × 4 silicene is estimated and found to be smaller than that of graphene. It is expected to result in higher electron mobility.

Prediction of the Iron-Based Polynuclear Magnetic Superhalogens with Pseudohalogen CN as Ligands.

To explore stable polynuclear magnetic superhalogens, we perform an unbiased structure search for polynuclear iron-based systems based on pseudohalogen ligand CN using the CALYPSO method in conjunction with density functional theory. The superhalogen properties, magnetic properties, and thermodynamic stabilities of neutral and anionic Fe2(CN)5 and Fe3(CN)7 clusters are investigated. The results show that both of the clusters have superhalogen properties due to their electron affinities (EAs) and that vertical detachment energies (VDEs) are significantly larger than those of the chlorine element and their ligand CN. The distribution of the extra electron analysis indicates that the extra electron is aggregated mainly into pseudohalogen ligand CN units in Fe2(CN)5¯ and Fe3(CN)7¯ cluster. These features contribute significantly to their high EA and VDE. Besides superhalogen properties, these two anionic clusters carry a large magnetic moment just like the Fe2F5¯ cluster. Additionally, the thermodynamic stabilities are also discussed by calculating the energy required to fragment the cluster into various smaller stable clusters. It is found that Fe(CN)2 is the most favorable fragmentation product for anionic Fe2(CN)5¯ and Fe3(CN)7¯ clusters, and both of the anions are less stable against ejection of Fe atoms than Fe(CN)n-x.

Crystal Structures, Stabilities, Electronic Properties, and Hardness of MoB2: First-Principles Calculations.

On the basis of the first-principles techniques, we perform the structure prediction for MoB2. Accordingly, a new ground-state crystal structure WB2 (P63/mmc, 2 fu/cell) is uncovered. The experimental synthesized rhombohedral R3̅m and hexagonal AlB2, as well as theoretical predicted RuB2 structures, are no longer the most favorite structures. By analyzing the elastic constants, formation enthalpies, and phonon dispersion, we find that the WB2 phase is thermodynamically and mechanically stable. The high bulk modulus B, shear modulus G, low Poisson's ratio ν, and small B/G ratio are benefit to its low compressibility. When the pressure is 10 GPa, a phase transition is observed between the WB2-MoB2 and the rhombohedral R3̅m MoB2 phases. By analyzing the density of states and electron density, we find that the strong covalent is formed in MoB2 compounds, which contributes a great deal to its low compressibility. Furthermore, the low compressibility is also correlated with the local buckled structure.

Investigation on the neutral and anionic BxAlyH2 (x + y = 7, 8, 9) clusters using density functional theory combined with photoelectron spectroscopy.

The structure and bonding nature of neutral and negatively charged BxAlyH2 (x + y = 7, 8, 9) clusters are investigated with the aid of previously published experimental photoelectron spectra combined with the present density functional theory calculations. The comparison between the experimental photoelectron spectra and theoretical simulated spectra helps to identify the ground state structures. The accuracy of the obtained ground state structures is further verified by calculating their adiabatic electron affinities and vertical detachment energies and comparing them against available experimental data. The results show that the structures of BxAlyH2 transform from three-dimensional to planar structures as the number of boron atoms increases. Moreover, boron atoms tend to bind together forming Bn units. The hydrogen atoms prefer to bind with boron atoms rather than aluminum atoms. The analyses of the molecular orbital on the ground state structures further support the abovementioned results.

[Effect of spacer on red and green phosphorescent organic light-emitting devices].

We have investigated the performances of organic light-emitting diodes (OLED) with different spacer, the structure was fabricated as ITO/MoO3 (40 nm)/NPB(40 nm)/TCTA(10 nm)/CBP:GIr114:R-4B2%(30 nm)/spacer (3 nm)/CBP: GIr114%:R-4B2%(30 nm)/BCP(10 nm)/Alq3 (40 nm)/LiF(1 nm)/Al(100 nm), the spacers were CBP, TCTA, TPBI and BCP separately, GIr1 and R-4B were green and red phosphorescent dye respectively. The results showed that compared to the reference device utilized CBP as the spacer layer, TCTA, TPBI and BCP had higher current efficiency in excess of 59%, 79% and 93%, the maximum current efficiency of 16.91 cd x A(-1) was achieved with BCP as the spacer at voltage of 5 V, TPBI and BCP as the spacer layer obtained the higher current density and lower efficiency roll-off. We attributed to these results to the follow reasons, the first was that carriers and excitons were limited to a narrow recombination region because of TCTA with higher LUMO energy level and triplet energy, which improved the probability of carriers recombination, in addition, more serious quenching at higher current density. The second reason was that TPBI and BCP had the higher HOMO energy level and electron mobility, which broadened excitons recombination zone. In addition, the spacer layer caused the accumulation of electrons or holes and the formation of high space electric field, leading to carrier injection and transport more effectively. In particular, we obtained a better stability of phosphorescent organic light-emitting diodes since the way for the red and green co-doped with host material.

[A new non-contact method based on relative spectral intensity for determining junction temperature of LED].

The high-power white LED was prepared based on the high thermal conductivity aluminum, blue chips and YAG phosphor. By studying the spectral of different junction temperature, we found that the radiation spectrum of white LED has a minimum at 485 nm. The radiation intensity at this wavelength and the junction temperature show a good linear relationship. The LED junction temperature was measured based on the formula of relative spectral intensity and junction temperature. The result measured by radiation intensity method was compared with the forward voltage method and spectral method. The experiment results reveal that the junction temperature measured by this method was no more than 2 degrees C compared with the forward voltage method. It maintains the accuracy of the forward voltage method and overcomes the small spectral shift of spectral method, which brings the shortcoming on the results. It also had the advantages of practical, efficient and intuitive, noncontact measurement, and non-destruction to the lamp structure.

[Influence of BCP on efficiency of red phosphorescent electroluminescent device].

The present paper uses the R-4B as phosphor dopant, the main body was CBP, regulation carrier composite layer was BCP, and the device structure was ITO/MoO3 (30)/NPB (40)/TCTA (10)/CBP : R-4B(6%)(15)/BCP(chi)/CBP : R-4B(6%) (15)/BCP(10)/Alq3 (40)/LiF/Al. In the device, chi was the thickness of the BCP with five different thickness of the device. At the same time, another contrast device was made, which had been optimized at MoO3 without regulated BCP layer. The result shows that the luminous area was 1.18 cm2, BCP was 4, MoO3 was 30 nm, its performance was the best, light voltage was 4 V, maximum efficiency was 18. 9 cd x A(-1), its corresponding EL main peak was at 612 nm, and color coordinates was (0.643, 0.353), getting stable and high efficient red phosphor OLED devices.

[Properties of phosphorescent organic light-emitting diodes with different doping order on light emitting layer].

Utilizing GIr1(green) and R-4B(red) phosphorescent dye, organic light-emitting diodes with different doping orders on red and green light-emitting layers were fabricated. The authors investigated the luminescent properties of devices combined with the effect of electron (TCTA) and hole (BCP) blocking layer. The results showed that the great impacts on spectrum, light efficiency, luminance and luminescent color were produced based on different doping order, and the authros also found the strong emission peak at the interface of the BCP and CBP layer. With the use of the red and green doping type, 0.527 mA x cm(-2), 104 cd x m(-2), 19.75 cd x A(-1) and (0.371 7, 0.576 8) could be reached, respectively. The reasons were that on the one hand, because of large difference between energy levels of host material CBP and doping material GIr1, R-4B, and charge trapping and hopping via dopants were the main mechanism of change; on the other hand, for the different energy levels between dopants and blocking layers, the doping sequence could affect barrier distribution, and then affect the electric field distribution.

[The influence of junction temperature on the white LED spectral characteristics of the mixture of the DCJTB and YAG : Ce3+].

The present paper mainly studies the influence of the junction temperature on the white LED spectral characteristics of the mixture of the DCJTB and YAG: Ce3+ phosphor. With layered coating of YAG phosphor and organic materials DCJTB on the LED chip with the method of hierarchical point powder, the color rendering index of the device will reach up to 90. The junction temperature can be measured conveniently and accurately with the integrated LED cooling pad which was developed by the laboratory. Experiments show that: the rise of the junction temperature can make the radiation amplitude of the blue chip decline continuously. The yellow radiation amplitude of YAG phosphor which is excited by radiation first increases and then decreases, the red spectrum is blue-shifted, the color rendering index of the device decreased linearly, while the color temperature first increases and then decreases.

[Spectral analysis of LED excited organic material MPPV].

By the method of spin-coating, a glass was coated with a layer of organic material MPPV dissolved in organic solvent tetrahydrofuran (THF). The radios of MPPV: THF were 25 mg: 1 mL, 50 mg: 1 mL, 100 mg: 1 mL and 150 mg: 1 mL. Then we irradiated the organic thin film by blue and white LED. The results showed that the blue and white LEDs could excite the organic material MPPV to emit red light in the region of 600-750 nm. And with the increase in the organic material MPPV, the color coordinate moved from (0.265 4, 0.248 9) to (0.395 4, 0.288 0) gradually. When the ratio of MPPV: THF was 100 mg: 1 mL, the white LED had the best color-rendering index of 86.1. The minimum of color temperature reached 2609K which was lower than that of white LED obtained by blue LED excited yellow YAG phosphor. Therefore, with the method of blue and white LED exciting the organic material MPPV, the color-rendering index and luminescence properties of LED could be improved significantly.

Enhancement of All-Inorganic Perovskite Solar Cells by Lead-Cerium Bimetal Strategy.

Owing to the instability of organic materials, an inorganic perovskite solar cell (PSC) attracts much attention in recent years. However, the instability of phase and overmuch traps lead to the inferior performance of inorganic perovskite solar cell, a high performance inorganic PSC is desirable. The element of cerium possesses a suitable chemical and physcial properties to substitute lead. We utilize cerium to partially substitute lead, a lead-cerium (Pb-Ce) bimetal based inorganic PSC is successfully achieved to modify the stability of PSC, the CsPb0.85Ce0.1I3 based PSC exhibits a champion PCE (power conversion efficiency) of 17.57%, and the tolerance of thermal, illumination, and environmental are enhanced among 10-20%. The enhanced PCE is ascribed to the structure of lead-cerium (Pb-Ce) bimetal perovskite absorbing layers and high quality of perovskite film.

[The spectrogram characteristics of organic blue-emissive light-emitting excitated YAG : Ce phosphor].

It is demonstrated that the panchromatic luminescence devices with organic blue-emissive light-emitting was fabricated. This technique used down conversion, which was already popular in inorganic power LEDs to obtain white light emission. A blue OLED device with a configuration of ITO/2T-NATA (30 nm)/AND : TBPe (50 Wt%, 40 nm)/Alq3 (100 nm)/LiF(1 nm)/Al(100 nm) was prepared via vacuum deposition process, and then coated with YAG : Ce phosphor layers of different thicknesses to obtain a controllable and uniform shape while the CIE coordinates were fine tuned. This development not only decreased steps of technics and degree of difficulty, but also applied the mature technology of phosphor. The results showed that steady spectrogram was obtained in the devices with phosphor, with a best performance of a maximum luminance of 13 840 cd x m(-2) which was about 2 times of that of the devices without phosphor; a maximum current efficiency of 17.3 cd x A(-1) was increased more two times more than the devices without phosphor. The emission spectrum could be adjusted by varying the concentration and thickness of the phosphor layers. Absoulte spectrogram of devices was in direct proportion with different driving current corresponding.

Understanding the structural transformation, stability of medium-sized neutral and charged silicon clusters.

The structural and electronic properties for the global minimum structures of medium-sized neutral, anionic and cationic Sin(µ) (n = 20-30, µ = 0, -1 and +1) clusters have been studied using an unbiased CALYPSO structure searching method in conjunction with first-principles calculations. A large number of low-lying isomers are optimized at the B3PW91/6-311 + G* level of theory. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable. The growth behaviors clearly indicate that a structural transition from the prolate to spherical-like geometries occurs at n = 26 for neutral silicon clusters, n = 27 for anions and n = 25 for cations. These results are in good agreement with the available experimental and theoretical predicted findings. In addition, no significant structural differences are observed between the neutral and cation charged silicon clusters with n = 20-24, both of them favor prolate structures. The HOMO-LUMO gaps and vertical ionization potential patterns indicate that Si22 is the most chemical stable cluster, and its dynamical stability is deeply discussed by the vibrational spectra calculations.