Effect of lithium and silver diffusion in single-stack and tandem OLED devices

A study of metal (Li, Ag) diffusion has been carried out in an archetypal OLED device based on N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine|tris(8-hydroxyquinolinato) aluminum|4,7-diphenyl-1,10-phenanthroline (NPB|Alq₃|Bphen). Using single-stack and two-stack tandem OLED structures with variations of layer thicknesses and metal layer placements, we have found that Ag vapor-deposited on Alq₃ layer can diffuse or penetrate deep into Alq₃, up to ∼2,000 Å, causing luminescence quenching. This diffusion can be substantially prevented by a thin layer of Li or Bphen deposited on Alq₃ prior to the deposition of Ag. In contrast, Li diffusion in either Alq₃ or Bphen is limited to about 50–100 Å. Li appears to be able to diffuse into Bphen irrespective of the order of Li and Bphen depositions.     

新型蓝光材料9，10-二萘蒽衍生物的合成及表征

通过引人不同烷基基团,采用亲核取代反应,设计与合成了3种新型9,10-二萘蒽类荧光材料,并研究了它们的紫外可见吸收、荧光发射等光物理性质.这些化合物在甲苯中均发射蓝色荧光,最大吸收和荧光发射峰分别为234～235 nm和431 nm,该类化合物具有较高的相对荧光量子效率,为ADN的1.2倍.它们具有130℃以上的玻璃化转变温度,最高的达到了179℃.以ITO/CFx/NPB/MDTBADN(EDTBADN,Tri-TBADN)/Alq3/LiF/A1为基本器件结构研究了电流密度和电压以及发光效率之间的关系.     

基于FHQZn发光的新结构有机黄光器件

利用一种新型材料(E)-2-(2-(9H-fluoren-2-yl)vinyl)quinolato-Zinc(FHQZn)制备了一种新结构的黄光OLED,器件的结构为:indium-tinoxide(ITO)/4,4′,4″-{N,-(2-naphthyl)-N-phenylamino}-triphenylamine(2T-NATA)(15nm)/FHQZn(xnm)/4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl(DPVBi)(20nm)/2,2′,2″-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole-(TPBi):6%factris(2-phenylpyridine)iridium(Ir(ppy)3)(45nm)/LiF(0.5nm)/Al,FHQZn作空穴传输层和黄色发光层,DPVBi作空穴阻挡层,TPBi中掺杂Ir(ppy)3作电子传输层;研究了发光层FHQZn的厚度对该器件的发光性能的影响。当FHQZn厚度x=25时,得到了效率和亮度最大的黄光器件,最大电流效率为1.31cd/A(at13V),最大亮度为5705cd/m2(at14V),此时色坐标为(0.4,0.5516)。     

Synthesis,characterization and conducting properties of novel poly (vinyl cinnamate)/zinc oxide nanocomposites via in situ polymerization

New polymer nanocomposite based on poly (vinyl cinnamate) (PVCin) with zinc oxide (ZnO) was synthesized by in situ polymerization of vinyl cinnamate with different concentrations of ZnO nanoparticles. The composite was characterized through FT-IR, FT-Raman, UV spectroscopy, XRD, HRTEM, FE-SEM, DSC, TGA and electrical conductivity studies. The IR, Raman and UV spectra ascertained the structural variation of PVCin network by the insertion of nanoparticles within the polymer segment. The morphological studies by TEM and FE-SEM photographs indicate that the nanopowder was uniformly dispersed in the polymer. The presence of nanoparticles in the nanocomposite was clearly observed from the XRD studies and the ordered arrangement of nanoparticles within the macromolecular chain of PVCin increased with increase in concentration of nanofillers. DSC results showed that the glass transition temperature and crystalline melting point were increased smoothly with the increase in concentration of nanoparticles. Analysis of TGA studies showed a significant increase in thermal stability with an increase in weight percentage of nanoparticles. The DC conductivity of nanocomposite was increased by ten orders of magnitude with the addition of 7 wt% of nano ZnO inclusion. AC conductivity, dielectric constant and dielectric loss tangent of nanocomposite was remarkably increased with increase in ZnO content up to 7 wt% of filler particles. Both AC and DC conductivity and dielectric properties were decreased beyond 7 wt% loading.     

Eu~(3+),Tb~(3+)共掺杂NaY(MoO_4)_2材料的制备及发光性能研究

采用水热法制备出NaY(MoO4)2:Eu3+,Tb3+下转换发光材料。通过X射线粉末衍射、红外光谱、荧光激发和发射光谱对其进行表征。讨论了不同反应温度及Eu3+掺杂浓度对NaY(MoO4)2:Eu3+,Tb3+的晶体结构和发光性能的影响,得到水热温度为180℃及Eu3+浓度为摩尔分数0.7%时,样品具有最佳的发光效果。在395nm光激发下,观察到了591nm处橙光发射峰以及616nm处强红光发射峰,分别对应于Eu3+的5D0→7F1和5D0→7F2跃迁。并研究了NaY(MoO4)2:Eu3+,Tb3+材料中Tb3+对Eu3+的敏化作用及能量传递过程。     

RCa_2Mg_2(VO_4)_3(R=Li,K,Na)荧光粉的制备及发光性能研究

采用高温固相法合成了RCa2Mg2(VO4)3(R=Li,K,Na)自激活系列荧光粉,并用X射线衍射仪和荧光分光光度计对合成样品的结构和发光性能进行了表征。结果表明:在750℃下煅烧得到的RCa2Mg2(VO4)3荧光粉具有较好的晶体结构。在331 nm的紫外光激发下,RCa2Mg2(VO4)3荧光粉在491 nm处具有较强的宽峰发射,其中Na Ca2Mg2(VO4)3的发光强度最好。Li Ca2Mg2(VO4)3、KCa2Mg2(VO4)3、Na Ca2Mg2(VO4)3的色坐标分别为(0.245,0.392)、(0.265,0.425)、(0.211,0.326),位于蓝绿光区。Eu3+掺杂后,Na Ca2Mg2(VO4)3:Eu3+样品光谱图中620 nm处出现Eu3+的发射峰,有效促使Na Ca2Mg2(VO4)3色坐标从蓝绿区(0.211,0.326)移到近白光区(0.260,0.322)。     

Poly(2-(N-carbazolyl)ethyl acrylate) as a host for high efficiency polymer light-emitting devices

Poly(2-(N-carbazolyl)ethyl acrylate), a poly(acrylate) comprised of carbazole-side groups attached via a flexible chain to the polymer backbone (PVAK) has been tested as host for solution-processed polymer light-emitting devices (PLEDs). This non-conjugated polymer proved to be an excellent candidate to host wide-bandgap phosphors. Notably, this polymer exhibited a high thermal stability (T_d = 322 °C), a glass transition temperature (T_g) of 91 °C and a wide bandgap corresponding to the pendent carbazole units and the disrupted π-conjugation of the polymer main chain, making this polymeric host a suitable candidate for wide bandgap triplet emitters. When tested as a host for FIrpic and Ir(ppy)₃, the resulting blue and green light-emitting devices showed a maximum luminous efficiency of 18.25 and 17.74 cd/A, respectively, which are comparable to recent reports of devices made using other carbazole-based oxygen-rich polymeric hosts. The polymer was also characterized by UV–visible absorption, photoluminescence spectroscopy as well as cyclic voltammetry.     

4, 6-Bis[3-(dibenzothiophen-2-yl)phenyl] pyrimidine bipolar host for bright,efficient and low efficiency roll-off phosphorescent organic light-emitting devices

A bipolar host 4, 6-Bis[3-(dibenzothiophen-2-yl)phenyl] pyrimidine (DBTPhPm) with small singlet-triplet splitting has been synthesized and confirmed through a series of photophysical and electrochemical properties. Monochromatic phosphorescent organic light-emitting devices (PHOLEDs) based on different hosts [(4,4′-N,N'-dicarbazole) biphenyl, 2,7-bis (diphenylphosphoryl)-9-[4-(N,Ndiphenylamino) phenyl]-9-phenylfluorene, (3,3'-bicarbazole) phenyl and DBTPhPm] and dopants are fabricated. Compared to other hosts, the DBTPhPm-based PHOLEDs exhibited high brightness, high efficiency and low efficiency roll-off. The maximum power efficiency of the DBTPhPm-based red (R), green (G), blue (B), yellow (Y), and orange (O) PHOLEDs are 12.2, 47.2, 17.6, 42.6 and 15.1 lm/W, respectively. The current efficiency roll-off of the R, G, B, Y, and O PHOLEDs are 29.8%, 8.6%, 18.2%, 5.9%, and 22.4% from the maximum current efficiency to the high brightness of 5000 cd/m². The detailed working mechanism of the DBTPhPm-based device is discussed.     

Synthesis,characterization, and antimicrobial activity of chitosan–zinc oxide/polyaniline composites

Organic–inorganic materials of chitosan–zinc oxide/polyaniline (CS–ZnO/PANI) composite were prepared via precipitation with a polymerization method and characterized by FT-IR, XRD, EDXS and TEM analysis, thereby providing evidence of composite formation. The size of the prepared CS–ZnO/PANI composite was found to be 100–200 nm, thereby rendering the morphology suitable for biomedical applications. Antibacterial activities of chitosan–ZnO (CS–ZnO), polyaniline (PANI) and CS–ZnO/PANI composites were determined against Gram-positive bacterium, Staphylococcus aureus (S. aureus), and Gram-negative bacterium, Pseudomonas aeruginosa (P. aeruginosa) and were tested in-vitro at 5–50 μg/mL. Results showed that CS–ZnO/PANI composite had broad-spectrum antibacterial activity that was greatly enhanced in comparison with CS–ZnO. In addition, CS–ZnO/PANI composite has tested fungal strains of Candida albicans (C. albicans) and relatively higher activities were observed than the known antibiotics. Finally, the antimicrobial activity of CS–ZnO/PANI composite against established biofilms was also examined and resulted in more than 95% inhibition in biofilm formation.     

Molecular p doping of 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl and n doping of 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene

This report details p-type doping of 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) with tetrafluorotetracyanoquinodimethane (F4-TCNQ) and n-type doping of 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi) with decamethylcobaltocene (DMC). Both CBP and TPBi are widely used as charge transport layers in organic light-emitting diodes (OLEDs). We confirm efficient p-type F4-TCNQ doping of CBP by observing, as a function of increasing dopant concentration, a shift of the Fermi level (E_F) toward the highest occupied molecular orbital (HOMO) in ultraviolet photoelectron spectroscopy (UPS) scans, a larger amount of fluorine in the film, a transition of the core C 1s electron levels to lower binding energies in X-ray photoelectron spectroscopy (XPS) measurements, and an increase of the current in vertical metal/organic semiconductor/metal devices, which in the context of the Gaussian Disorder Model, can be attributed to an injection barrier lowering and a charge carrier concentration enhancement. In the case of doping of TPBi with DMC, as the dopant concentration increases, a shift of E_F away from the HOMO in UPS and a transition of the core C 1s electron levels to higher binding energies in XPS are observed, both of which are indicative of n-type doping. The presence of inherent degradation of TPBi films during UPS measurements is also established. These findings may pave the way for development of higher performance OLEDs based on doped transport layers.     

Structural, electrical and optical properties of zinc oxide produced by oxidation of zinc thin films

We have investigated the effects of oxidation temperature on the physical properties of polycrystalline zinc oxide thin films. Zinc thin films are oxidized at different temperatures in air. We have found that increasing the oxidation temperature deteriorates the preferred c-axis orientation. Also, increasing the oxidation temperature enlarges the crystal size and increases the number of needle-shaped crystals on the surface of the ZnO samples. By increasing the oxidation temperature, more than zinc melting point, tensile stresses start to build up in the films. Also by increasing temperature, sheet resistance of the films decreases, while photoluminescence intensity ratio (green to orange) increases. Increasing the oxidation temperature reduces the transparency of the films, too. It is proposed that either an increase in the number of oxygen vacancies or a decrease in the volume of grain boundaries, is responsible for the observed behavior of the films at higher oxidation temperatures.     

Electronic and optoelectronic properties of zinc phthalocyanine single-crystal nanobelt transistors

ZnPc single-crystal nanobelts were grown by a physical vapor transport process with the length ranging from 20 to 150 μm and the width ranging from several tens of nanometers to several micrometers. Based on high crystalline ZnPc nanobelts, its single-crystal nanobelt transistors were realized. The field-effect mobility is as high as 0.75 cm²V⁻¹s⁻¹ with OTS modified SiO₂ as dielectric, which is the highest value for the reported ZnPc devices. In addition, ZnPc nanobelt transistors show the excellently photosensitive properties with the high photoswitching ratio (|I_light/I_dark|) of 7.34 × 10³ and the high photoresponsivity at 1.57 × 10⁴ AW⁻¹. These results indicate the future potential of ZnPc single-crystal transistors in organic electronic and optoelectronic applications.     

Structure,charge-transfer and luminescent properties of bis(2-(2-hydroxyphenyl)benzothiazolate)beryllium

A luminescent Be(II) complex of aromatic N, O-chelate ligand, namely Be(BTZ)₂ (BTZ = 2-(2-hydroxyphenyl)benzothiazolate), has been synthesized and characterized by X-ray crystallography. Its charge-transfer and luminescent properties were studied. The results indicated that the single crystal of Be(BTZ)₂ is monoclinic, space group C2/c. With larger the electron-transfer rate than hole-transfer rate, Be(BTZ)₂ may serve as candidate for electron-transport material. The highest occupied molecular orbital energy level (E_HOMO) and the lowest unoccupied molecular orbital energy level (E_LUMO) are −5.79 eV and −2.98 eV, respectively. Be(BTZ)₂displays strong photoluminescence (PL) in the blue region at 456 nm, and the electroluminescent (EL) peak wavelength is located at 460 nm, CIE coordinates are X = 0.1525, Y = 0.1803.     

1.54 μm Near-infrared photoluminescent and electroluminescent properties of a new Erbium (III) organic complex

The crystal structure of Er(PM)₃(TP)₂ [PM = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone, TP = triphenyl phosphine oxide] was reported and its photoluminescence properties were studied by UV–vis absorption, excited, and emission spectra. The Judd–ofelt theory was introduced to calculate the radiative transition rate and the radiative decay time of 3.65 ms for the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ion in this complex. The antenna-effect and phonon-assisted energy-transfer were introduced to discuss the intramolecular energy transfer from ligands to Er³⁺ ion. Based on this Er(III) complex as the emitter, the multilayer phosphorescent organic light emitting diode was fabricated with the structure of ITO/NPB 20 nm/Er(PM)₃(TP)₂ 50 nm/BCP 20 nm/AlQ 40 nm/LiF 1 nm/Al 120 nm, which shows the typical 1.54 μm near-infrared (NIR) emission from Er³⁺ ion with the maximum NIR irradiance of 0.21 μW/cm².     

Electrical properties and luminescence of CuInSe2

We have studied the electrical properties and luminescence spectra of melt-grown CuInSe₂ single crystals and the doping of the crystals with intrinsic defects and extrinsic impurities. The preparation and the properties of p-n junctions are also discussed. We find that the low temperature photoluminescence spectra of crystals as-grown or annealed between 400 and 700 C are characteristic of the conductivity type. At 77 K, p-type crystals emit in a band peaked at 1.00 eV (type A spectrum) whereas the emission of n-type crystals peaks at 0.93 eV (type B spectrum). Type A and type B spectra can be interchanged by alternate anneals in minimum or maximum Se pressure. Type B emission dominates the electroluminescence spectrum of p-n junctions. These features are explained by the appearing and disappearing of a donor level as a consequence of annealing in vacuum or in Se atmosphere. We find that Zn and Cd act as donors. Crystals doped with these impurities have electron concentrations above 10¹⁸ cm⁻³. Zn-dopped samples exhibit a very broad recombination band below the bandgap in photoluminescence both at 77 and 300 K.     

Effect of four different zinc salts and annealing treatment on growth,structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition

ZnS thin films were deposited from four different zinc salts on glass substrates by chemical bath deposition method. Different anions of zinc salts affect the deposition mechanism and growth rate, which influence the properties of the films significantly. The ZnS thin film deposited from ZnSO₄ is smoother, thicker, more homogeneous and compact, nearly stoichiometric, comparing with the films deposited from Zn(CH₃COO)₂ and Zn(NO₃)₂, and ZnCl₂. The scratch test of bonding force between ZnS film and substrate shows that the ZnS film deposited from ZnSO₄ has the most excellent adhesion with the substrate. The presence of SO₄²⁻ promotes heterogeneous ZnS thin film growth via ions by ions deposition, and the films deposited from Zn(CH₃COO)₂ and Zn(NO₃)₂ are formed via clusters by clusters deposition. XRD and HRTEM results show that cubic ZnS films are obtained after single deposition, and the grain size of ZnS thin film deposited from ZnSO₄ for 2.5 h is 10 nm. The average transmission of all films is greater than 85% in the wavelength ranging from 600 to 1100 nm, and the transmission of films deposited from ZnSO₄ or Zn(NO₃)₂ for 1.5, 2 and 2.5 h is greater than 85% in the wavelength varying from 340 to 600 nm, which can enhance the blue response. The band gaps of all ZnS thin films are in the range of 3.88–3.99 eV. After annealing treatment, the mechanical and optical properties of the ZnS thin film deposited from ZnSO₄ are improved significantly.     

Computational studies of electronic structures and photophysical properties of luminescent iridium(III) complexes based on amidinate/bis(pyridylphenyl) ligands

To provide a deeply understanding of the nature of the emissive origin as well as the radiative and nonradiative processes, theoretical studies have been performed on four amidinate/bis(pyridylphenyl) iridium(III) complexes. It has been testified that they have exhibited bright yellowishgreen phosphorescence emission with moderate photoluminescence quantum yields. Besides geometries, electronic structure, absorption and phosphorescence spectra, and the factors governing the radiative decay rate constants of the emissive state have been examined. Additionally, this work also explores the potential energy profiles of the deactivation pathway via the triplet mental-centered states. Among these complexes, complex 2, which contains the bulky t-butyl group on the amidinate nitrogen atoms, presents the highest internal quantum yield. To explore more efficient phosphors, three novel phosphors, 2a, 2b, and 2c have been designed on the basis of complex 2 by incorporation of substituents on the bis(pyridylphenyl) ligand with a slightly higher quantum yield.     

Optical,electrical and photovoltaic properties of thermally evaporated 3-amino-2-[(2-nitrophenyl)diazinyl]-3-(piperidin-1-yl)acrylonitrile thin films

Thin films with various thickness of 3-amino-2-[(2-nitrophenyl)diazinyl]-3-(piperidin-1-yl)acrylonitrile (ANPA) were produced by conventional thermal evaporation. The dependence of the optical, electrical, and photovoltaic properties on the film thickness was investigated. X-ray diffraction showed that the films have an amorphous structure. The optical properties were investigated in terms of transmittance and reflectance in the spectral range 200–2500 nm. Spectral distribution analysis of the absorption coefficient revealed that the films have an indirect allowed electronic interband transition. The optical bandgap decreased from 2.47 to 2.1 eV for an increase in film thickness from 105 to 265 nm. The direct current electrical conductivity of the films was measured for sandwich-structured samples as a function of the heating temperature and film thickness. The films exhibited semiconductor behavior and electrical conduction was attributed to hopping of charge carriers in localized states. ANPA films of differing thickness were deposited on p-type Si single-crystal substrates. The influence of film thickness on the electrical and photovoltaic parameters of Au/ANPA/p-Si/Al heterojunction solar cells was investigated.     

AgIn共掺杂(AgIn)xPb1-2xTe化合物的合成及热电传输性能

用高温熔融法合成了Ag和In共掺的单相n型(AgIn)xPb1-2xTe化合物,研究了(AgIn)掺杂量x对(Ag-In)xPb1-2xTe(x=0.01～0.05)物相组成及热电性能的影响.结果表明:掺杂量x≤0.04时得到单相四元化合物,x=0.05时样品中出现了组成为AgInTe2第二相;(AgIn)xPb1-2xTe化合物的Seebeck系数随着x增加而增大,电导率随着掺杂量x增加而降低;化合物的热导率随着掺杂量x增大而减小;当x=0.01时,(AgIn)xPb1-2xTe化合物的热电性能指数值最大,在800K时达到1.1.