三吸附子STM系统图像解释研究

应用激子动力学方法描述扫描隧道显微镜隧道中电子运动的动力学行为新方案，得到了三吸附子扫描隧道显微镜系统图像解释公式的解析形式。     

Management of charge carriers and excitons for efficient and color-stable white phosphorescent organic light-emitting diodes with simplified structure

We have demonstrated color-stable and highly efficient simplified white phosphorescent organic light-emitting diodes. The key feature is the use of a novel approach to confine the distribution of charge carriers and excitons across the whole blue emission layer. The resulting two-color white device has the maximum power efficiency and current efficiency of 45.5 lm/W and 43.5 cd/A with a very low color shift over a wide range of luminance. By systematically investigating the working mechanisms, we found that the ambipolar charge carrier transport ability of co-host layer which ensures the distribution of excitons to form in the whole blue emission layer was the critical factors for constructing color-stable white devices. Our results show that simplified white devices based on two organic materials achieving excellent color stability are possible.     

Correlation between interlayer thickness and device performance in blue phosphorescent organic light emitting diodes with a quantum well structure

We systematically examined the effects of interlayer (ITL) thickness variation in an emission layer (EML) on electrical and optical characteristics of blue phosphorescent organic light-emitting diodes. The EML consisted of a quantum well structure using a hole transport material 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) as an ITL. This ITL facilitated the confinement of charge carriers in the recombination zone (RZ), adjusted the charge carrier balance in the EML, and prevented the triplet exciton loss to adjacent transport layers. The thickness variation in the ITL greatly influenced the size and location of the RZ and the exciton density (ED), which is related to charge balance and exciton diffusion in the EML. A micro-cavity effect around 500 nm and the corresponding redshift/blueshift in the electroluminescent spectrum arose from different ITL thicknesses. Remarkably, the device having a 5-nm-thick TAPC ITL showed better current and power efficiencies than those of any other devices because of the rearrangement of the locations of excitons and ED through control of the hole/electron charge density.     

Femtosecond Dynamics in Single Wall Carbon Nanotube/Poly(3-Hexylthiophene) Composites

Femtosecond transient absorption measurements on single wall carbon nanotube/poly(3-hexylthiophene) composites are used to investigate the relaxation dynamics of this blended material. The influence of the addition of nanotubes in polymer matrix on the ultrashort relaxation dynamics is examined in detail. The introduction of nanotube/polymer heterojunctions enhances the exciton dissociation and quenches the radiative recombination of composites. The relaxation dynamics of these composites are compared with the fullerene derivative-polymer composites with the same matrix. These results provide explanation to the observed photovoltaic performance of two types of composites.     

Excitation functions of (n, α) reaction cross-sections for some important isotopes from threshold to 20 MeV

The (n, α) reaction cross-sections from threshold to ∼20 MeV on some important nuclides ⁴²Ca, ^50,53Cr, ^56,57Fe, ^58,62Ni, and ^63,65Cu involved in the reactor shielding design have been calculated using the Hauser–Feshbach statistical model with preequilibrium effects by involving PCROSS option in Empire 2.19. The transmission coefficients for neutrons in the entrance channel are calculated using the optical model potential of Koning. In the exit channel optical model potential of Avrigeanu has been used. The experimental values have been chosen carefully for all the isotopes, from EXFOR data base. The calculations are compared with existing experimental data as well as with evaluated data files (ENDF/B-VI.0 and JENDL-3.3). A good agreement between the calculated and experimental data validates the nuclear model approaches with increased predictive power to supplement and extend the nuclear database that is required for several applications.     

Spectrally dependent photocurrent generation in aggregated MEH-PPV:PPDI donor–acceptor blends

Films of MEH-PPV and PPDI blends with weight ratio 1:2 have been prepared by spin-coating and annealing between 0 and 60 min at 95 °C. The films were characterized by absorption spectroscopy and atomic force microscopy (AFM). The main emphasis has been on the photon conversion efficiency in the photovoltaic cells as a function of excitation wavelength and applied voltage/electric field. Site selective excitation at wavelengths at which either non-aggregated bulk PPDI or dimers/aggregates of PPDI absorb prove that (i) the rate-limiting process for power conversion is the field-assisted escape of optically generated geminate electron–hole pairs from their mutual coulombic potential and (ii) the photogeneration yield depends on the donor–acceptor topology. A significant difference of the yield has been noted when alkoxy-pendent groups in MEH-PPV are replaced by phenyl-alkoxy groups.     

Quantitative estimation of exciton quenching strength at interface of charge injection layers and organic semiconductor

The performance of polymer light emitting diodes (PLEDs) degrades due to exciton quenching at the interface with charge injection layers and electrodes. We investigate the photo-physics of singlet excitons in Poly (9, 9-dioctylfluorene-alt-benzothiadiazole) (F8BT) conjugated polymer interfaced with various commonly used hole and electron injection layers. Absolute, steady-state and transient photoluminescence (PL) studies are carried out on pristine F8BT film and films with injection layer/F8BT to understand the role of injection layers on exciton quenching. Exciton quenching by the charge injection layers is treated by accounting for both exciton diffusion and the non-radiative transfer of energy to the charge injection layer. The non-radiative transfer of energy is modelled using dipole-dipole interaction theory coupled with diffusion of excitons, from which we obtain the exciton capture radius (x₀) in the range of 1–7 nm. We also correlate x₀ with PL decay time (τ) using the relation τ α 1/x₀³. The steady-state PL yield for each case also shows correlation with the PL decay lifetime. This study provides interesting insight on the selection criterion for injection layer to be used in PLEDs for minimizing optical losses while preserving the electronic injection properties.     

Improved efficiency and stability in polymer solar cells using a Tetra-nuclear Zinc(II) complex interfacial layer

Tetra-nuclear Zinc(II) complex Zn₄O(AID)₆ [AID = 7-azaindolate] is a wide band gap luminescent material that exhibits efficient emission matching the absorption spectra of organic donor materials such as polythiophene (P3HT). This work demonstrates polymer solar cells (PSC) based on P3HT:PCBM (phenyl-C₆₁-butyric acid methyl ester) blend active layer with a Zn₄O(AID)₆ cathode interfacial layer achieving a power conversion efficiency (PCE) significantly higher than that of the reference devices. The energy level and impedance spectroscopy analysis show that the Zn₄O(AID)₆ cathode interfacial layer acts as an efficient exciton/hole blocking layer, and reduces charge recombination rate with more efficient electron extraction. The Zn₄O(AID)₆ interfacial layer also helps achieve longer lifetime of PSC devices. The improved efficiency and stability combined with low cost and nontoxicity of Zn₄O(AID)₆ make it a promising cathode interfacial material for high-performance and stable PSC devices.     

Low-temperature photoluminescence study of exciton recombination in bulk GaAsBi

The exciton recombination processes in a series of elastically strained GaAsBi epilayers are investigated by means of time-integrated and time-resolved photoluminescence at T = 10 K. The bismuth content in the samples was adjusted from 1.16% to 3.83%, as confirmed by high-resolution X-ray diffraction (HR-XRD). The results are well interpreted by carrier trapping and recombination mechanisms involving the Bi-related localized levels. Clear distinction between the localized and delocalized regime was observed in the spectral and temporal photoluminescence emission.