Potential barrier and photovoltage at interfaces of hexadecafluoro-copper-phthalocyanine and copper phthalocyanine films on the surface of tin dioxide

Potential barrier formation during the deposition of ultrathin coatings of copper phthalocyanine (CuPc) and hexadecafluoro-copper-phthalocyanine (F₁₆CuPc) on the surface of polycrystalline tin dioxide and during the deposition of F₁₆CuPc coatings over a CuPc film is studied. A photoinduced change in the surface potential of the prepared structures upon exposure to light in the visible wavelength region is detected. The surface photovoltage of the studied organic films has a positive sign with respect to the substrate, its spectral dependences correspond to the absorption spectra of the organic materials CuPc and F₁₆CuPc. Surface potential measurements are performed using a probe beam of low-energy electrons, based on the total current spectroscopy technique. A total decrease in the work function by 0.2 eV is detected during the deposition of a CuPc film up to 8 nm in thickness on a SnO₂ substrate; in the case of the F₁₆CuPc/SnO₂ interface, an increase in the work function by 0.55 eV is detected. At the initial deposition stage, at organic film thicknesses of up to 1.5 nm, the interfacial potential barrier corresponded to electron density transfer from the organic film to the substrate in both cases of CuPc/SnO₂ and F₁₆CuPc/SnO₂. It is assumed that the photoinduced change in the surface potential is caused by charge-carrier separation in a boundary region up to 1.5 nm thick.     

Preparation of highly oriented copper phthalocyanine film by molecular templating effects for organic field-effect transistor

Highly oriented copper phthalocyanine (CuPc) film consisting of many crystal domains was prepared by introducing titanyl-phthalocyanine (TiOPc) as molecular template at high substrate temperature. CuPc molecules stand up on the top of TiOPc domains exhibiting herringbone structure and high-order arrangement investigated by atomic force microscopy and X-ray diffraction. Then organic transistors were fabricated that exhibited improved device performances, a 0.12 cm²/V s of mobility and a 10⁵ of on/off ratio. Furthermore, template thickness dependence on device performance was disclosed. These results indicated that molecular template is a very effective method to prepare high-mobility organic semiconductor film.     

Low voltage copper phthalocyanine organic thin film transistors with a polymer layer as the gate insulator

Low voltage organic thin film transistors(OTFTs) were created using polymethyl-methacrylate-co g-lyciclyl-methacrylate(PMMA-GMA) as the gate dielectric.The OTFTs performed acceptably at supply voltages of about 10 V.From a densely packed copolymer brush,a leakage current as low as 2×10~(-8) A/cm~2 was obtained.From the measured capacitance-insulator frequency characteristics,a dielectric constant in the range 3.9-5.0 was obtained. By controlling the thickness of the gate dielectric,the threshold voltage ...     

基于聚合物绝缘栅的低电压有机薄膜晶体管

利用甲基丙烯酸甲酯-甲基丙烯酸环氧丙脂为栅绝缘层制备了酞箐铜有机薄膜晶体管,在电压为10V时器件具有较好的性能,栅绝缘层的漏电流密度低至2×10-8A/cm2 。测量其电容特性,该绝缘薄膜的介电常数介于3.9-5.0 。通过对绝缘层的减薄,阈值电压由 -3.5V 升至-2.0V,该酞箐铜有机薄膜晶体管可以在低电压下工作,其场效应迁移率为1.2×10-3 cm2/Vs 。     

异质诱导生长的酞菁铜薄膜晶体管的研究

因酞菁薄膜平面具有多电子共轭大π键结构,本文采用异质诱导的方式对酞菁薄膜的生长特性进行了改善研究。采用高掺杂硅为栅极,氧化硅为绝缘层,生长α-四噻吩或p-六联苯薄膜为异质诱导层,制备了酞菁铜有机薄膜晶体管。利用原子力显微镜研究薄膜生长特性,并对比研究了2种诱导层对薄膜晶体管性能的影响。实验结果表明:α-四噻吩上生长的酞菁铜薄膜,形貌呈片状,而p-六联苯上生长的酞菁铜薄膜,形貌呈针状,均与单层酞菁铜棒状形貌不同。同时,α-四噻吩与p-六联苯薄膜上生长酞菁铜后,两者晶体管电性能都有不同程度的提高,均比单层酞菁铜提高了1~2个数量级,表明α-四噻吩或p-六联苯对酞菁铜薄膜均有诱导效应,可以获得高性能的有机薄膜晶体管。     

Dielectric response and electric properties of organic semiconducting phthalocyanine thin films

The dielectric function of some phthalocyanine compounds (ZnPc, H₂Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ε₁, varies strongly with frequency and temperature. The frequency dependence was expressed as: ε₁ = Aωⁿ, where the index, n, assumes negative values (n < 0). In addition, the imaginary part of the dielectric constant, ε₂, is also frequency and temperature dependent. Data analysis confirmed that ε₂ = Bω^m with values of m less than zero. At low frequencies and all temperatures, a strong dependence is observed, while at higher frequencies, a moderate dependence is obvious especially for the Au-electrode sample. Qualitatively, the type of electrode material had little effect on the behavior of the dielectric constant but did affect its value. Analysis of the AC conductivity dependence on frequency at different temperatures indicated that the correlated barrier hopping (CBH) model is the most suitable mechanism for the AC conduction behavior. Maximum barrier height, W, has been estimated for ZnPc with different electrode materials (Au and Al), and had values between 0.10 and 0.9 eV. For both electrode types, the maximum barrier height has strong frequency dependence at high frequency and low temperatures. The relaxation time, τ, for ZnPc and FePc films increases with decreasing frequency. The activation energy was derived from the slopes of τ versus 1/T curves. At low temperatures, an activation energy value of about 0.01 eV and 0.04 eV was estimated for ZnPc and FePc, respectively. The low values of activation energy suggest that the hopping of charge carriers between localized states is the dominant mechanism.     

First-principles calculation of atomic configurations of carbon and tin near the surface of a silicon thin film used for solar cells

To achieve higher engineering efficiency in solar cells, group-IV compound semiconductors, such as silicon (Si) or germanium (Ge), in the form of thin films containing carbon (C) and/or tin (Sn) atoms, are gaining attention as alternatives to poly-silicon crystals. Atomic configurations of C and Sn atoms near the (001) surface of a Si thin film were analyzed by first-principles calculation based on density functional theory (DFT). The results of the analysis are threefold. First, C and Sn atoms are most stable at the first atomic layer of the Si thin film, and the surface does not affect the stability of C or Sn atoms deeper than the fifth layer. Second, C and Sn atoms deeper than the fifth layer do not affect the stability of newly arrived C and Sn atoms at the surface during film growth. The effects of the (001) surface and interacting C and/or Sn atoms on the thermal-equilibrium concentrations of C and Sn in each layer of the Si thin film were evaluated in consideration of the degeneracy of the atomic configurations. Third, in the case of mono-doping, formation energy of C (Sn) at the (001) surface increases with increasing concentration of surface C (Sn). In the case of co-doping at C/Sn concentration ratio of 1:1, the formation energies of C and Sn decrease with increasing surface concentrations of C and Sn. It is concluded from these results that co-doping enhances the incorporation of C and Sn atoms in the Si thin film.     

Enhancing charge transport in copper phthalocyanine thin film by elevating pressure of deposition chamber

Copper phthalocyanine (CuPc)-based thin film transistors were fabricated using CuPc films grown under different deposition pressure (P_dep) (ranging from 1.8 × 10⁻⁴ Pa to 1.0 × 10⁻¹ Pa). The transistor performance highly depended on P_dep. A field-effect mobility of 2.1 × 10⁻² cm²/(V s) was achieved under 1.0 × 10⁻¹ Pa. Detailed investigations revealed that P_dep modulates the molecular packing and orientation of the organic films grown on a SiO₂/Si substrate and influences the charge transport. Furthermore, from a device physics point of view, contact resistance of the fabricated transistors decreased when P_dep increased, which was beneficial in reducing energy consumption.     

Influence of oxygen on the parameters of a thin film copper phthalocyanine field effect transistor

The influence of oxygen on the electrical parameters of a copper phthalocyanine thin film field effect transistor was investigated by means of temperature‐modulated field effect spectroscopy. It was found that both the dark electrical conductivity and threshold voltage of the source–drain current versus gate voltage dependence were changed after oxygen exposure. Both effects can be effectively utilised for gas sensing. Copyright © 1999 John Wiley & Sons, Ltd.     

The working mechanism of organic photovoltaic cell by using copper phthalocyanine as exciton blocking layer

We demonstrate the working mechanism of organic photovoltaic (OPV) cell with copper phthalocyanine (CuPc) as exciton blocking layer (EBL). The new EBL material CuPc, commonly has been used as electron donor in the organic solar cells due to its electron-donating and hole-transporting properties. But here we proves that the α-polymorph CuPc layer can transfer electrons to Al cathode through the half-filled b_1g level, this mechanism is different from that of general EBL material with larger band gap and electron-transporting property, which is based on damage states induced by the heat of evaporating Al.     

Study of the surface structure of tin dioxide layers for gas sensors by atomic-force microscopy

This paper presents the results of a study by atomic-force microscopy of tin dioxide layers as a function of the conditions under which they are doped with iodine and tellurium during the production of the layers by thermal vacuum deposition of tin, followed by oxidation. Data concerning the atomic-force microscopy of layers fabricated in various processing regimes are presented and discussed. It is shown that introducing volatile impurities into the starting charge is an effective means of modifying the surface structure of the layers and of altering the character of its microsurface. The temperature dependence of the sensitivity of the layers to toluene vapor is studied and analyzed. Fiz. Tekh. Poluprovodn. 32, 654–657 (June 1998)     

Temperature dependence of electroluminescence degradation in organic light emitting devices without and with a copper phthalocyanine buffer layer

Temperature dependence of electroluminescence degradation was investigated in two types of organic light emitting devices (OLEDs) based on tris(8-hydroxyquinoline) aluminum (AlQ₃) emitter molecule, one without and another with copper phthalocyanine (CuPc) buffer layer at the hole-injecting contact interface. Electroluminescence degradation in time was measured for devices operated at 22 and 70 °C. Results unexpectedly showed that devices without the CuPc buffer layer demonstrated negligible change in half-life when operated at 22 or 70 °C, while devices with the CuPc layer showed the expected decrease in half-life when the temperature was increased. The results are explained within the framework of recently proposed OLED degradation mechanism, which identifies AlQ₃ cations as unstable, leading to device degradation.     

Growth of quaterrylene thin films on a silicon dioxide surface using vacuum deposition

Quaterrylene molecules, which have a planar and highly π-conjugated chemical structure, were deposited on a SiO₂ surface, and their thin film structures, including surface morphology and molecular orientation, were examined by atomic force microscopy (AFM) and X-ray diffractometry (XRD). AFM observations revealed the grain size and surface roughness to be closely dependent on the substrate temperature in the range from 27 °C to 200 °C. Particularly at a substrate temperature of 140 °C, grain sizes of up to 6 μm and low surface roughness of 1.67 nm were successfully obtained in the 8 ML-thick film. XRD measurements of the quaterrylene thin film revealed (0 0 l) Bragg reflections, corresponding to a spacing of 1.89 nm. This value coincides with the average height of the terraces of the stepped structure observed in the AFM images. These results clearly demonstrate the quaterrylene molecules to have an upright orientation and that thin films grow as layered structures on the surface. From the full width of half maximum (FWHM) of the XRD rocking curve, the degree of alignment of the molecular planes (mosaicity) was estimated to be 0.09°, which shows that the film has a highly ordered structure.     

Physicochemical properties of the surface and near-surface region of epitaxial n-GaAs layers modified by atomic hydrogen

Changes in the static electrical parameters of the Au-GaAs Schottky barriers in the (n-n ⁺)-GaAs structures treated with atomic hydrogen are closely related to modification of the chemical properties of the surface layers in these structures, including changes in the rate of n-GaAs etching in a DMF-monoethanol amine (1:3) solution, in the electrochemical deposition rate and the structure of the resulting Au layer, and in the degree of passivation of linear defects emerging on the surface. The unprotected surface of epitaxial n-GaAs(100) layer exhibited virtually no etch pits upon the treatment in atomic hydrogen at 100°C. For n-GaAs protected with a 50-Å-thick SiO₂ film, a drop in the etching rate and a considerable decrease in the number of etch pits, as well as a decrease in the thickness of electrochemically deposited gold layer and a change in is structure, were observed for the samples treated in atomic hydrogen at all temperatures in the range studied (100–400°C).     

Enhancing conversion efficiency of inverted organic solar cells using Ag nanoparticles and long wavelength absorbing tin (II) phthalocyanine

Wide wavelength inverted organic solar cells (IOSCs) were fabricated and characterized by doping the active layer with long wavelength absorbing tin (II) phthalocyanine (SnPc). The hole-transporting layer (HTL) comprised Ag nanoparticles (NPs)-embedded poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The short-circuit current density (J_sc) and power conversion efficiency (PCE) were considerably enhanced. It is attributed to that Ag NPs result in the enhancement of the scattering and reflection of light, leading to increase absorption efficiency in the active layer of IOSCs. Moreover, the SnPc-doped active layer exhibits a long wavelength absorption and prevents the active layer from degradation by PCBM clusters. The optimized IOSCs exhibited an open circuit voltage (V_oc), J_sc, fill factor (F.F.), and PCE of 0.5 V, 10.34 mA/cm², 45.33% and 2.33%, respectively, under simulated AM1.5G illumination at 100 mW/cm².     

Effect of Pt, Pd, Au additives on the surface and in the bulk of tin dioxide thin films on the electrical and gas-sensitive properties

The microstructure and properties of thin (??100 nm) SnO₂ films with noble metals Pt, Pd, Au additives, grown by dc magnetron deposition are studied. It is shown that the introduction of additives into the bulk and the deposition of dispersed catalysts on the semiconductor surface make it possible to control the sensor parameters in pure air and upon exposure to reduction (CO, H₂, CH₄) and oxidation (NO₂) gases. Possible mechanisms for the effect of Pt, Pd, Au on the bulk and surface properties of tin dioxide are discussed. The technological conditions for film growth, which provide the selective detection of low concentrations (10?C100 ppm) of CO and H₂, below-explosive concentrations (0.5?C2.5 vol %) of methane, and trace concentrations (0.05?C5 ppm) of NO₂ are determined.     

Implication of molecular orientation on charge transport and gas sensing characteristics of cobalt–phthalocyanine thin films

Charge transport and gas sensing characteristics of cobalt phthalocyanine films deposited along (ATB) and perpendicular (PTB) to the natural twin boundaries of (0 0 1) LaAlO₃ substrate have been investigated. The charge carrier mobility of ATB films (∼5 cm² V⁻¹ s⁻¹) is five orders of magnitude higher compared to that of PTB films (∼7 × 10⁻⁵ cm² V⁻¹ s⁻¹), suggesting that twin boundaries acts like a template for ordering of molecules. The ATB films on exposure to ammonia showed a reversible increase of resistance, with fast response and recovery. In contrast PTB films showed same sensitivity, but exhibits base resistance drift along with sluggish response.     

Photocatalytic degradation of organic dye using titanium dioxide modified with metal and non-metal deposition

In this study, photocatalytic degradation of methyl orange (MO) as an example of organic dye was investigated using different wt% Pd-loaded and N-doped P-25 titanium dioxide (TiO₂) nanoparticles, as example of metal and nonmetal-doped TiO₂, respectively. The Pd-loaded and N-doped TiO₂ photocatalysts were prepared by post-incorporation method using K₂PdCl₄ and urea, respectively, as precursors. A variety of surface analysis techniques were used for characterization of surface and functional group while using ultraviolet/visible (UV–vis) analysis for monitoring photocatalytic degradation of MO. Kinetic parameters were obtained using Langmuir-Hinshelwood model to determine the degradation rate constants. It was found that the metal-loaded titanium dioxide degraded MO in water at a higher rate than did non-metal-loaded titanium dioxide fabricated by using the post-synthesis method. Also, the pure P25-TiO₂ degraded MO more than N-doped TiO₂ because of decreased surface area by particle agglomeration after being made by the post-incorporation method.     

Thermal and electroless deposition of copper on poly(tetrafluoroethylene-co-hexafluoropropylene) films modified by surface graft copolymerization

Surface modification of Ar plasma-pretreated poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film via UV-induced graft copolymerization, under atmospheric conditions, with 4-vinylpyridine (4VP), 2-vinylpyridine (2VP) and 1-vinylimidazole (VIDz) was carried out to improve the adhesion with the thermally evaporated and the electrolessly deposited copper. The surface composition and structure of the graft-copolymerized FEP films were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), respectively. The electroless plating of copper on the graft-copolymerized FEP film could be carried out in the absence of sensitization by SnCl/sub 2/ (the Sn-free activation process). The adhesion strength of the thermally evaporated and the electrolessly deposited copper on the FEP surfaces was affected by the type of monomers used for graft copolymerization and the surface graft concentration. The T-peel adhesion strengths of the electrolessly deposited copper on the 4VP, 2VP and VIDz graft-copolymerized FEP films with 90-s of Ar plasma pretreatment were about 9.8 N/cm, 7.3 N/cm and 4.9 N/cm, respectively.     

Thermally induced structural changes and optical properties of tin dioxide nanoparticles synthesized by a conventional precipitation method

Tin dioxide (SnO₂) nanoparticles were synthesized by a conventional precipitation method using the reaction between tin chloride pentahydrate and ammonia solutions. The obtained powders were calcined at varied temperatures from 300 to 1050 °C, and then characterized by using thermogravimetric analysis, differential thermal analysis and Fourier transformation infrared spectroscopy. The average crystallite size, determined by x-ray diffraction, was found to be in the range of 3.45–23.5 nm. The analysis exhibited a tetragonal phase. The activation energy of crystal growth was calculated and found to be 12.12 kJ/mol. The microstructure of nanoparticles was examined by high resolution transmission electron microscopy. Optical properties were investigated by a UV–vis absorption spectrophotometer. The calculated optical band gap lies between 4.75–4.25 eV as a result of increasing the calcination temperatures and crystallite size.