Theoretical and experimental study of photocurrent action spectrum of ITO/sexithiophene/Al structure

We have studied photovoltaic cells using sexithiophene in (ITO/6T/Al) structure, and we have measured the action spectrum obtained by illumination through the aluminum side which is compared to the measured absorption spectrum. Two models were used to interpret this experiment: the Ghosh model using the carriers diffusion property in the bulk, and the kinetic model describing the dynamic behavior of the charge carriers in the device. The confrontation of these models with the experimental spectra allows us to reach the diffusion length of electron–hole pair L=2×10⁻⁶ cm. We also give the mobility of carriers (μ_n≈1.5×10⁻⁴ cm²/V s, and μ_p≈1.5×10⁻⁵ cm²/V s) and their diffusion coefficients (D_n≈4×10⁻⁶ cm²/s, and D_p≈4×10⁻⁷ cm²/s).     

Transparent conductive Sb-doped SnO2/Ag multilayer films fabricated by magnetron sputtering for flexible electronics

The effects of an embedded silver layer and substrate temperature on the electrical and optical properties of Sb-doped SnO₂ (ATO)/silver (Ag) layered composite structures on polyethylene naphthalate substrates have been investigated. The highest conductivity of ATO/Ag multilayer films was obtained with a carrier concentration of 1.5 × 10²² cm^?3 and a resistivity of 2.4 × 10^?5 Ω cm at the optimum Ag layer thickness and substrate temperature. The photopic averaged transmittance and Haacke figure of merit are 81.7%, and 21.7 × 10^?3 Ω^?1, respectively. In addition, a conduction mechanism is proposed to elucidate the mobility variation with increased Ag thickness. We also describe the influence of substrate temperature on the structural, electrical and optical properties of the ATO/Ag multilayer films, and propose a mechanism for the changes in electrical and optical properties at different substrate temperatures.     

Third-order nonlinear optical property of poly(2,5-dihexyloxy)-p-phenylene vinylene modified by N+ ion implantation

A soluble poly(2,5-dihexyloxy)-p-phenylene vinylene (PDHOPV) was prepared via dehydrochlorination reaction from hydroquinone and n-hexyl bromide as raw materials. The PDHOPV films implanted by 20 keV nitrogen ions (N⁺) in the dose range of 3.8 × 10¹⁵–9.6 × 10¹⁶ ions/cm² were characterized by UV–vis absorption spectra, which showed the optical absorption was raised gradually in the visible region followed by a red shift of optical absorption threshold and the band gap (E_g) was reduced from 2.12 eV to 1.71 eV with the increase of ion dose. The third-order nonlinear optical (NLO) susceptibilities (χ⁽³⁾) were measured by degenerate four-wave mixing (DFWM) technique at 532 nm. The results demonstrated that the χ⁽³⁾ value of PDHOPV film could be enhanced effectively by means of N⁺ ion implantation. When the ion dose was 3.8 × 10¹⁶ ions/cm², the χ⁽³⁾ value of PDHOPV film was maximized to 1.06 × 10⁻⁸ esu which was almost eleven times larger than that of the pristine film. Moreover, the mechanism responsible for the variation of χ⁽³⁾ value of PDHOPV film with N⁺ ion dose was also discussed tentatively.     

Synthesis and characterization of triphenylamine derivatives by oxidative polymerization

Hole transport polymers consisting of 4-methoxytriphenylamine (P-MOTPA) and 4-n-butyltriphenylamine (P-BTPA) were synthesized by oxidative coupling reaction using FeCl₃ as an oxidant. These polymers had good solubility and their thin films showed sufficient morphological stability. ¹H NMR and ¹³C NMR revealed that the monomers were exclusively connected at the p-positions of unsubstituted phenyl groups. Polymers had UV absorption maximum around 370 nm. Cyclic voltammograms of polymers showed well-defined pairs of reduction and oxidation peaks at 1.1 V versus Ag/AgCl, indicating that the polymers are electrochemically active. P-MOTPA and P-BTPA had hole drift mobility of being 4.04 × 10⁻⁵ and 2.98 × 10⁻⁵ cm²/V s at the electric field of 50 V/μm, respectively.     

Synthesis,crystal structure and two-photon absorption of a cadmium complex constructed by DMIT ligand

The cadmium complex [(CH₃)₄N][Cd(C₃S₅)₂]·H₂O constructed by 1,3-dithiole-2-thione-4,5-dithiolato (DMIT) ligand has been synthesized and its structure has been determined by means of X-ray single crystal diffraction. Its two-photon absorption (TPA) has been studied in acetonitrile solution using open-aperture Z-scan technique with 20 picosecond (ps) pulses at wavelength 1064 nm. Its TPA coefficient β was determined to be 4.475 × 10^?10 m/W, corresponding the TPA cross-section σ₂ is 3.95 × 10^?53 (m⁴ s/photon molecule).     

Strain rate sensitivity of a high strain rate superplastic TiNp/2014 Al composite

The effects of deformation temperature and strain in hot rolling deformation on strain rate sensitivity of the TiN_p/2014 Al composite were studied by tensile tests conducted out at 773, 798, 818 and 838 K with the strain rates from 1.7 ×10^?3 to 1.7 × 10⁰ s^?1. It is shown that the curves of m value of the TiN_p/2014Al composite deformed at different temperatures can be divided into two stages with the variation of strain rate, and the critical strain rates are 10^?1 s^?1. The optimum deformation temperature of the TiN_p/2014 Al composite is near incipient melting temperature of 816 K and the optimum strain rate is a little higher than the critical strain rate. The effect of deformation temperature on strain rate sensitivity is relative to liquid phase helper accommodation. The effect of strain in hot rolling deformation on strain rate sensitivity attributes to change of microstructure and deformation mechanism.     

Cationic and radical polymerization of N-vinyl-2-phenylpyrrole: Synthesis of electroconducting,paramagnetic and fluorescent oligomers

Cationic polymerization of N-vinyl-2-phenylpyrrole (catalysts: Me₃SiCl, CF₃COOH, BF₃·OEt₂, HCl, WCl₆, FeCl₃, complex LiBF₄–dimethoxyethane, catalysts concentration 1–2 wt%, 20–70 °C, 24–48 h) affords oligomers (molecular weight 1400–1700) of a unexpected structure with alternating 2-phenylpyrrole and ethylydene units, the yields reaching 63%. The oligomers structure has been supported by isolation and identification of the corresponding dimer, N-vinyl-2-phenyl-5-[N-(2-phenyl-1H-pyrrol-1-yl)ethyl]-1H-pyrrole. Radical polymerization of the same monomer (AIBN, 1.5–4 wt%, 60–80 °C, 40–60 h or UV irradiation or both) gives oligomers (molecular weight 2100–3000) of normal structure having polyethene backbone with pendant 2-phenylpyrrole groups in up to 40% yields. The oligomers of both types are semiconductors (1.3 × 10^?6–3.6 × 10^?6 S/cm) after doping with I₂, paramagnetic (4.2 × 10¹⁷–8.7 × 10¹⁷ g^?1) and fluorescent in a near UV region (λ 355–363 nm, acetonitrile).     

The interdependence of structural and electrical properties in TiO2/TiO/Ti periodic multilayers

Multilayered structures with 14–50 nm periods composed of titanium and two different titanium oxides, TiO and TiO₂, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO₂/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO₂ and rutile phase. DC electrical resistivity ρ measured for temperatures ranging from 300 to 500 K exhibited a metallic-like behaviour (ρ_473K = 1.05 × 10^?5 to 1.45 × 10^?6 Ω m) with a temperature coefficient of resistance ranging from 1.20 × 10^?3 K^?1 for the highest period (Λ = 50.0 nm) down to negative values close to ?4.97 × 10^?4 K^?1 for the smallest one (Λ = 14.0 nm). A relationship between the dimensions of periodic layers and their collective electrical resistivity is proposed where the resistivity does not solely depend on the total thickness of the film, but also depends on the chemical composition and thickness of each sub-layer. Charge carrier mobility and concentration measured by the Hall effect were both influenced by the dimension of TiO₂/TiO/Ti periods and the density of ionized scattering centres connected to the titanium concentration in the metallic sub-layers.     

Controlling of silicon–insulator–metal junction by organic semiconductor polymer thin film

Electrical and photovoltaic properties of a metal–semiconductor–insulator–polymer–metal diode were investigated. The n-Si/SiO₂/MEH-PPV/Al diode shows a rectifying behavior with the rectification ratio of 2.22 × 10⁵ at ±5 V and exhibits a non-ideal behavior due to the series resistance and oxide-organic layers. The organic semiconductor makes a contribution to the I–V characteristics of the diode and the trap-charge limited space charge and space charge limited current mechanisms were observed for the diode. The current–voltage characteristics of the n-Si/SiO₂/MEH-PPV/Al diode under different illumination intensities give an open circuit voltage (V_oc) along with a short circuit current (I_sc). This suggests that the n-Si/SiO₂/MEH-PPV/Al diode is a photovoltaic device with V_oc = 0.456 V and J_sc = 7.89 × 10^?8 A/cm² values under 100 mW/cm² illumination intensity. The photoconductivity mechanism of the diode is controlled by monomolecular recombination. The interface state density D_it values with time constant τ_it of the diode under dark and illumination conditions were found to be 2.53 × 10¹⁰ eV^?1 cm^?2 with 5.09 × 10^?5 s and 2.50 × 10¹⁰ eV^?1 cm^?2 with 8.27 × 10^?5 s, respectively. The obtained results indicate that the n-Si/SiO₂/MEH-PPV/Al diode is a photo-sensitive diode.     

Ions transport and self-doping in layer-by-layer conducting polymer films

The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10⁻⁴ and 3.56 × 10⁻⁴ g/C for the Li⁺ and (C₂H₅)₄N⁺ doped films, and is different for the cast POMA film, i.e., 11.3 × 10⁻⁴ for Li⁺ and 6.45 × 10⁻⁴ g/C for (C₂H₅)₄N⁺. Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li⁺ or (C₂H₅)₄N⁺, are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.     

The effect of a novel organic compound chiral macrocyclic tetraamide-I interfacial layer on the calculation of electrical characteristics of an Al/tetraamide-I/p-Si contact

The Al/tetraamide-I/p-Si Schottky barrier diode (SBD) has been prepared by adding a solution of a novel nonpolymeric organic compound chiral macrocylic tetraamide-I in chloroform on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward-bias current–voltage (I–V) characteristics of Al/tetraamide-I/p-Si SBD with a barrier height value of 0.75 eV and an ideality factor value of 1.77 showed rectifying behaviour. The energy distribution of the interface state density determined from I–V characteristics increases exponentially with bias from 5.81 × 10¹² cm⁻² eV⁻¹ at (0.59-E_v) eV to 1.02 × 10¹³ cm⁻² eV⁻¹ at (0.40-E_v) eV. It has showed that space charge limited current (SCLC) and trap charge limited current (TCLC) are the dominant transport mechanisms at large forward-bias voltages.     

Protonation-induced rearrangements in Langmuir films and redox properties of Langmuir–Blodgett films of 2-(n-alkyl)fulleropyrrolidines

The effect of protonation of the pyrrolidine ring nitrogen of 2-(n-alkyl)fulleropyrrolidines, C₆₀pyr–C_m (m=4, 6, 8, 10 and 12), on the properties of the Langmuir and Langmuir–Blodgett (LB) films was investigated. The isotherms of both surface pressure (π) and surface potential change (ΔV) versus area per molecule (A) for the Langmuir films of C₆₀pyr–C_m were determined simultaneously. It was found that the longer the alkyl chain of the fulleropyrrolidine the larger is the film compressibility, κ, i.e., κ(C₆₀pyr–C₄)=(2.1±0.4)×10⁻² m mN⁻¹, κ(C₆₀pyr–C₈)=(3.5±0.4)×10⁻² m mN⁻¹ and κ(C₆₀pyr–C₁₂)=(4.1±0.5)×10⁻² m mN⁻¹, as expected for the liquid surface films. The values of surface area at zero surface pressure (A₁) differ in the range 0.6 nm² molecule⁻¹ (for m=4–8) to 1.4 nm² molecule⁻¹ (for m=10–12), indicating that all 2-(n-alkyl)fulleropyrrolidines form multilayer or aggregated films on neutral water subphase. However, acidification of the water subphase increases the A₁ values for all investigated fulleropyrrolidines up to ca. 1.9 nm² molecule⁻¹, i.e., the value corresponding to maximum area occupied by a fulleropyrrolidine at horizontal orientation in a monolayer film. Apparently, 2-(n-alkyl)fulleropyrrolidinium cations formed at low pH are markedly de-aggregated in the films and their orientation is changed due to protonation of the pyrrolidine nitrogen. Similarly, however, less pronounced effects are observed if ionic strength of the subphase solution, I, is increased in the range 0≤I≤1.0 mol dm⁻³ NaCl. The Langmuir films formed on a water subphase were the most stable with respect to the LB transfer onto 5 MHz Au–quartz crystal vibrators. Simultaneous cyclic voltammetry and piezoelectric microgravimetry at an electrochemical quartz crystal microbalance of these films showed at least two electroreductions where the fulleropyrrolidine mono anions were stable with respect to dissolution.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Synthesis,crystal structure and thermal behavior of Na4[B10O16(OH)2]·4H2O

New hydrated sodium borate Na₄[B₁₀O₁₆(OH)₂]·4H₂O has been synthesized under mild hydrothermal conditions at 170 °C. The structure was determined by single-crystal X-ray diffraction and further characterized by FT-IR, Raman spectra and DTA-TG. It crystallizes in the monoclinic space group Pc with a unit cell of dimension a = 11.323(2) Å, b = 6.5621(14) Å, c = 12.244(3) Å, α = 90°, β = 91.050(3)°, γ = 90°, V = 909.7(3) Å³, Z = 2. The crystal structure of Na₄[B₁₀O₁₆(OH)₂]·4H₂O consists of Na–O polyhedra and [B₁₀O₁₆(OH)₂]⁴⁻ polyborate anions. Dehydration of this compound occurs in three steps and leads to an amorphous phase which undergoes crystallization.     

Thermoelectric properties of silver-doped n-type Bi2Te3-based material prepared by mechanical alloying and subsequent hot pressing

Effect of Ag-doping on thermoelectric properties of n-type Bi₂(Te_0.94,Se_0.06)₃ is studied. Bulk Bi₂(Te_0.94,Se_0.06)₃ sample with single solid solution phase and high relative density (over 95%) is obtained by mechanical alloying and subsequent hot press sintering. The as-sintered sample has a microstructure of randomly distributed plate grains and its size is about 1 μm. A V-shaped variation for the electrical properties with Ag doping is found which corresponds to different Ag atomic position in lattice among the doping range studied. A maximum figure of merit of about 1.7 × 10⁻³/K is achieved.     

Extraction of electronic parameters of organic diode fabricated with NIR absorbing functional manganase phthalocyanine organic semiconductor

The semiconducting and metal/organic semiconductor properties of the newly synthesized NIR absorbing α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties {M[Pc(S–CH₃CH₂(OH)CH₂(OH))]₄X}(M = Mn^III) have been investigated by electrical conductivity–temperature, optical absorption and current–voltage characteristics methods. The electrical conductivity increases with the temperature, suggesting that the peripheral α-substituted-functional manganase phthalocyanine is an organic semiconductor. The optical band gap and trap energy values were determined and were found to be 2.98 eV and 1.95 eV, respectively. The ITO/MnPc/Al diode shows a rectifying behavior due to the formation of MnPc/Al interface with a rectification ratio of 29.4 at ±2 V. The series resistance R_s and ideality factor n values were found to be 102.6 kΩ and 8.89, respectively. The interface state density for the diode was of order of 2.73 × 10¹¹ eV^?1 cm^?2 with the interface time constant of 1.93 × 10^?5.It is evaluated that newly synthesized α-substituted manganase phthalocyanine bearing functional 2,3-dihydroxypropylthio moieties is an organic semiconductor and can be used in electronic device applications as an organic diode.     

The calculation of electronic properties of an Ag/chitosan/n-Si Schottky barrier diode

In this study, the film of chitosan by adding the solution of chitosan being a polymeric compound on the top of an n-Si substrate and then by evaporating solvent was formed. It was seen that the chitosan/n-Si contact demonstrated clearly rectifying behavior and the reverse curves exhibit a weak bias voltage dependence by the current–voltage (I–V) curves studied at room temperature. Average barrier height and ideality factor values for this structure were determined as 0.94 eV and 1.81, respectively. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitosan/n-Si substrate in the energy range (E_c−0.785) to (E_c−0.522) eV have been determined from the I–V characteristics. The interface state density N_ss ranges from 5.39 × 10¹² cm⁻² eV⁻¹ in (E_c−0.785) eV to 1.52 × 10¹³ cm⁻² eV⁻¹ in (E_c−0.522) eV. The interface state density has an exponential rise with bias from the midgap towards the bottom of the conduction band.     

Stoichiometric interfaces of Al and Ag with Al2O3

Atomic geometries and adhesive energetics as computed from first principles are presented for stoichiometric Al(111)/Al₂O₃(0001) and Ag(111)/Al₂O₃(0001) interfaces and for the Al₂O₃(0001) surface. At both the interfaces and the alumina surface we found substantial interplanar relaxations within the alumina. We found the Al₂O₃(0001) surface energy to be 2150 mJ/m², in reasonable agreement with earlier results. Interfacial energies varied only 10–15% over the 3 primary sites we investigated for each metal/alumina combination. For Al/Al₂O₃, we found the metal equilibrium configuration to be atop Al atoms of the alumina, with a work of adhesion of 1078 mJ/m². For Ag/Al₂O₃, the work of adhesion is determined to be 672 mJ/m², and we found the Ag atoms to be in the (3-fold oxygen) hollow sites. These works of adhesion appear to be reasonably consistent with experimental data for solid Al or Ag on Al₂O₃, but allowance for nonstoichiometry in the interface (work in progress) may be important for this quantity. Finally, we discuss the accuracy of improved exchange–correlation potential approximations.     

Two new nickel(II) complexes: Synthesis and third-order optical nonlinearity

Two new nickel(II) complexes were synthesized and characterized by UV, MS and elemental analysis. Their off-resonant third-order nonlinear optical properties were measured using femtosecond laser and degenerate four-wave mixing technique. The third-order nonlinear optical susceptibilities χ⁽³⁾ are 3.38 × 10^?13 esu and 3.64 × 10^?13 esu. The nonlinear refractive index n₂ are 6.22 × 10^?12 esu and 6.70 × 10^?12 esu. The second-order hyperpolarizabilities γ of the molecules are 3.38 × 10^?31 esu and 3.65 × 10^?31 esu. The response times are 61 fs and 74 fs. The results show that the two complexes have potential nonlinear optical applications.     

Synthesis,crystal structure and electrical conductivity of [bmim][Ni(dmit)2]3 (bmim = 1-butyl-3-methylimidazolium,dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

A new complex [bmim][Ni(dmit)₂]₃ has been prepared, and its crystal structure and electrical conductivity where determined and measured. Crystallographic parameters for C₂₆H₁₅N₂S₃₀Ni₃: triclinic system; space group: P-1; a=12.760(3), b=19.441(4), c=11.670(2) Å; α=102.00(3), β=117.10(3), γ=95.06(3)°; Z=2, R=0.0579 (I>2σ(I)). The conductivity of this salt at room temperature is 1.7×10⁻² S cm⁻¹ and it shows semiconduction in the temperature range of 110–290 K.