New fluoranthene-based cyanine dye for dye-sensitized solar cells

In this paper, a new fluoranthene-based unsymmetrical organic cyanine dye I and the corresponding cyanine dye II containing ethynyl unit for the purpose of comparison were designed and synthesized as sensitizers for the application in dye-sensitized solar cells (DSSCs). The absorption spectra, electrochemical and photovoltaic properties of I and II were extensively investigated. The DSSCs based on the fluoranthene dye I showed the better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 67%, a short-circuit photocurrent density (J_sc) of 7.83 mA cm^?2, an open-circuit photovoltage (V_oc) of 0.476 V, and a fill factor (ff) of 0.63, corresponding to an overall conversion efficiency of 2.34% under simulated AM 1.5G solar light condition. Also, the effects of chenodeoxycholic acid (CDCA) in a solution as a co-adsorbate on the photovoltaic performance of DSSCs based on cyanine dyes were also investigated. The presence of CDCA for 0.5 h, increases both the photovoltage and photocurrent of the DSSC incorporating I, in which the photovoltage and photocurrent increase 9.3% and 20%, respectively. The above photovoltaic results indicate that coadsorption of appropriate amount CDCA is effective to improve solar cell performance.     

Photovoltaic properties of poly(terthiophene) doped with light-harvesting dyes and photocurrent generation mechanism

A range of commercially available anionic dyes were successfully incorporated as dopants during the electrodeposition of poly(terthiophene) (P(TTh)). Photovoltaic testing revealed that the best photoelectrochemical cell (PEC) was based on P(TTh) doped with Sulforhodamine B, which showed short-circuit-current (I_sc) = 178 μA cm⁻², open-circuit-voltage (V_oc) = 318 mV, fill-factor (FF) = 29.6% and power-conversion-efficiency (PCE) = 0.0334% under white light illumination intensity of 500 W m⁻². Photocurrent action spectroscopy of the PECs based on dye-doped P(TTh)s prepared here, and of the PECs prepared in a previous study, showed that only a cationic dye directly contributed to photocurrent, while anionic dyes did not. It is proposed that these observations are due to attractive or repulsive electrostatic interactions between dyes and the electron acceptor I₃⁻ at the polymer/electrolyte interface.     

Photo-induced magnetization in copper(II) octacyanomolybdate(IV)

The photomagnetic effect of the mixed-valence compound Cu₂^II[Mo^IV(CN)₈]·7.6H₂O (Cu^II; 3d⁹, S=1/2, Mo^IV; 4d², S=0) (1) was investigated. The UV–VIS spectra showed the intervalence transfer (IT) band between Mo^IV–CN–Cu^II and Mo^V–CN–Cu^I around 500 nm. When the paramagnetic compound 1 was irradiated by a filtered blue light (400–430 nm, 3 mW/cm²) of a Xe lamp at 5 K, the irradiated sample exhibited a spontaneous magnetization with a Curie temperature of 17 K. By annealing the irradiated sample above 200 K, the magnetic property of this sample returned to the initial state. This photo-induced magnetization is explained by the following mechanism. The excitation of the IT band causes the electron transfer from Mo^IV (S=0) to Cu^II (S=1/2), producing a mixed-valence isomer of Mo^V (S=1/2)–CN–Cu^I (S=0). However, half of the copper ions remain as Cu^II ions due to the stoichiometric limitation and hence the irradiated 1 is expressed as Cu^ICu^II[Mo^V(CN)₈]·7.6H₂O. The unpaired electrons on Mo^V (S=1/2) ions and those on Cu^II (S=1/2) ions in the irradiated compound interact ferromagnetically, giving rise to the spontaneous magnetization.     

Photovoltaic devices based on polythiophenes and substituted polythiophenes

In recent years there has been considerable interest in the fabrication of photovoltaic devices using polymeric and organic materials. This paper presents work carried out using a range of polythiophenes, including some substituted with porphyrin moieties as light harvesters. Homopolymers and copolymers were investigated for their performance in photovoltaic devices, and the use of both solid polymer electrolyte and liquid electrolyte was examined. Both photoelectrochemical cells and Schottky devices were investigated. The best photoelectrochemical cell was fabricated using polyterthiophene which had V_oc=139 mV, I_sc=123.4 μA cm⁻², fill factor=0.38, and energy conversion efficiency=0.02% at a halogen lamp intensity of 317 W m⁻². The Schottky device gave a V_oc=0.5 V and I_sc of 0.98 μA cm⁻² at a halogen lamp intensity of 500 W m⁻².     

Flexible N-channel organic phototransistor on polyimide substrate

We report a flexible photoresponsive organic field-effect transistor, phototransistor (OPT), based on a fluorinated copperphthalocyanine (F₁₆CuPc) and polymer gate dielectric on a flexible polyimide substrate. Under light illumination, the device exhibited a photoresponsivity of 2.15 mA/W at V_GS = 2 V and optical power of 5.66 mW/cm². The current ratio (I_photo/I_dark) of the light to dark states was calculated to be around 300 at V_GS = 2 V. Furthermore, the switching time of the phototransistor was found to be lower than 0.1 s. When the substrate was bent outward up to a bending radius of 4.4 mm, the device still showed photoresponsive field-effect characteristics. However, the photoresponsivity and I_photo/I_dark ratio decreased with decreasing bending radius. These results indicate that the present flexible OPT could potentially be used in optoelectronic device applications.     

Micrometer-scaled OFET channel patterns fabricated by using PEDOT/PSS microfibers

We have easily fabricated channel patterns of organic field-effect transistors (OFETs), in which channel lengths were 5 μm, by using wet-spun poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) microfibers with diameters of ca. 5 μm. Pentacene-based FETs with a top-contacted configuration, showed a hole mobility of 0.13 cm² V^?1 s^?1 and on/off current ratio of 9.4 × 10⁴. The device also showed large current of ca. 160 μA (V_D = ?50 V; V_G = ?50 V), reflecting shorter channel length of the devices. We have evaluated self-assembled monolayer (SAM) through measurements of water contact angle and by Zisman plot. As a result, critical surface tension of the octadecyltrichlorosilane (OTS)-treated SiO₂ surface is 17 mN m^?1 which is consistent with that of well-known SAM. We also well analyzed the cross-sections of the device by a scanning transmission electron microscopic (STEM) technique. The results indicated that the thicknesses of the pentacene layer in the channel part and Au layer in the source/drain part were ca. 30 and 30 nm, respectively. Furthermore, it is also indicated that the 100-nm grains of the pentacene were well adhered on the surface of the SAM-formed SiO₂ layer.     

Improved mobility of the copper phthalocyanine thin-film transistor

Copper phthalocyanine (CuPc) organic thin-film transistor (OTFT) was fabricated by thermal evaporation deposition on p-SiO₂ dielectric layer. Organic thin-film transistors used in large display areas need the enhancement of transistor performances by increasing the I_on/I_off ratio and the mobility. The output and transfer characteristics of CuPc-OTFT having source/drain interdigitated-finger geometry were investigated. The mobility, I_on/I_off ratio and inverse sub-threshold slope for the CuPc-OTFT were found to be 5.32 × 10^?3 cm² V^?1 s^?1, 1.94 × 10⁴ and 2.5 V/decade, respectively. The interface state density of the transistor was found to be 3.73 × 10¹¹ eV^?1 cm^?2 using the conductance-frequency method. The CuPc film indicated a homogeneous surface having 3.878 nm small roughness values as observed by atomic force microscope (AFM) measurements. The obtained results indicate that we have improved a CuPc-OTFT transistor with high mobility without being of any substrate treatment.     

Design and synthesis of a novel class of inhibitors for mild steel corrosion in acidic and carbon dioxide-saturated saline media

p-(9-(2-Methylisoxazolidin-5-yl)nonyloxy)benzaldehyde I, prepared using a cycloaddition protocol, was elaborated into its cinnamaldehyde derivative II which upon quarternization with propargyl chloride afforded III bearing an interesting blend of structural traits suitable for imparting inhibition of mild steel corrosion. Novel compounds I–III showed efficient inhibition against mild steel corrosion in CO₂–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar), 1, 4, 7.7 M HCl, and 0.5 M H₂SO₄ at 60 °C as determined by gravimetry and electrochemical methods. The presence of carbonaceous surface and nitrogen, as revealed by XPS study, indicated the formation of a film covering the metal surface, which imparted corrosion inhibition.     

Sintering behavior and non-linear properties of ZnO varistors processed in microwave electric and magnetic fields at 2.45 GHz

A study of the densification behavior and grain growth mechanisms of ZnO-based varistors composed of 98 mol.% ZnO–2 mol.% (Bi₂O₃, Sb₂O₃, Co₃O₄, MnO₂) has been carried out. The pressed samples were sintered in microwave electric (E) and magnetic (H) fields using a single-mode cavity of 2.45 GHz. The effect of the sintering temperature (900–1200 °C), holding time (5–120 min) and sintering mode (E, H) on the microstructure and electrical properties of the sintered varistor samples were investigated. The grain growth kinetics was studied using the simplified phenomenological equation Gⁿ = kte^(?Q/RT). The grain growth exponent (n) and apparent activation energy (Q) values were estimated for both electric and magnetic heating modes and were found to be n = 3.06–3.27, Q = 206–214 kJ mol^?1, respectively. The lower value of n estimated in the E field was attributed to a volume diffusion mechanism, whereas the higher n value in the H field sintering was correlated mainly to a combined effect of volume and surface diffusion processes. Samples sintered in the H and E fields showed high final densities. Moreover, the ones sintered in the H field presented slightly higher density values and bigger grains for all sintering temperatures than E field heated ones. The optimal sintering conditions were achieved at 1100 °C for a 5 min soaking time for both H and E field processed samples, where respectively densities of 99.2 ± 0.5% theoretical density (TD) and 98.3 ± 0.5% TD along with grain size values of G = 7.2 ± 0.36 μm and G = 6.6 ± 0.33 μm were obtained. Regarding the electrical properties, breakdown voltage values as high as 500–570 V mm^?1 were obtained, together with high non-linear coefficients α = 29–39 and low leakage currents (J_l ≈ 5 × 10^?3 mA cm^?2), respectively, for E and H field sintered varistor samples. Moreover, samples sintered in an H field systematically exhibited higher breakdown voltage values compared to the ones sintered in the E field. This was attributed to an improved coupling between the H field and the present dopants within the ZnO matrix, this latter being mostly semiconductive, thus leading to an enhanced reactivity and improved properties of the electrostatic barrier.     

A study of optical properties and annealing effect on the absorption edge of pristine- and iodine-doped polyazomethine thin films

Aromatic polyazomethine (PPI) thin film have been obtained by chemical vapor deposition (CVD) method, via polycondensation process and characterized by X-ray diffraction, AFM, FTIR and detailed UV–Vis–NIR studies. Optical transmission and fundamental reflectivity spectra of the film have been examined within the spectral range 200–2500 nm. The refractive index (n), film thickness (d) and parameters of the absorption edge i.e. the optical gap (E_G) and the Urbach energy (E_U) have been found for the PPI film before and after iodine (I₂) doping. Then the annealing effect (from 25 °C every 25 °C up to 225 °C) on the absorption edge have been investigated during “in situ” spectral measurements. Amorphous character of the films allowed us to obtain the E_G and E_U values, in the way typical for amorphous semiconductors. As a result of iodine doping, the energy gap of the PPI film (2.19 eV) distinctly reduces to 1.73 eV, due to the polaron states and, simultaneously, the Urbach energy decreases. Thermal stability of the pure PPI film, being the typical feature of polyazomethines, was confirmed, while after iodine doping the film turned out to be thermo-stable only below 100 °C; then the distinct changes of the optical gap and the Urbach energy, connected with the iodine releasing process, have been presented and discussed.     

Electrochemical corrosion behaviors of straight WC–Co alloys: Exclusive variation in grain sizes and aggressive media

The electrochemical corrosion behaviors of straight WC–10Co cemented carbides with grain sizes of 1.2, 2.6, 6.1 and 8.2 μm, were comparatively investigated in the solutions of NaOH (pH = 13), Na₂SO₄ (pH = 7) and H₂SO₄ (pH = 1) respectively. To insure a sole variable of WC grain sizes, specific magnetic saturation values of the alloys are adjusted to be identical. The results show a good linear dependence for R_ct (charge transfer resistance) and I_corr (corrosion current density) against the grain sizes. A high sensitivity of the grain sizes to both R_ct and I_corr are identified in NaOH and H₂SO₄. In the solutions of NaOH and Na₂SO₄, the alloys with smaller WC grain sizes exhibit better corrosion resistances, while the alloys with larger WC grain sizes exhibit better corrosion resistances in H₂SO₄. Additionally, in terms of the corrosiveness, NaOH is the weakest and H₂SO₄ is the most aggressive for all the alloys. The corrosion mechanisms were discussed in light of the SEM surface observation, X-ray photoelectron spectroscope analysis and the electrical equivalent circuits for electrochemical impedance spectroscopy.     

Large spectral shifts of electronic transitions in MoSI molecular wire dispersions as a function of bundle diameter

A systematic study of optical absorption spectra of Mo₆S_9?xI_x (x = 6) molecular wire dispersions in ethanol, fractionated into different bundle diameter populations shows that electronic transitions shift significantly as a function of bundle diameter. Two electronic transitions show significant shifts: the Mo–S charge transfer peak shifts from 1.8 to 1.5 eV and the next inter-band transition shifts from 2.7 to 2.4 eV with increasing bundle diameter d, in the range 5–100 nm. This empirical observation hugely simplifies characterization of Mo₆S_9?xI_x wire dispersions according to diameter, opening the way to rapid advances in processing of these materials. We discuss the possible origin of the shift, dismissing quantum size effects, impurities and solvatochromism as well as stoichiometric variations between x = 6 and x = 4.5.     

The characterization of structure,thermal stability and magnetic properties of Fe–Co–B–Si–Nb bulk amorphous and nanocrystalline alloys

Recently bulk amorphous alloys have attracted great attention due to their excellent magnetic properties. The glass-forming ability of bulk amorphous alloys depends on the temperature difference (ΔT_x) between glass transition temperature (T_g) and crystallization temperature (T_x). The increase of ΔT_x causes a decrease of the critical cooling rate (V_c) and growth of the maximum casting thickness of bulk amorphous alloys. The aim of the present paper is to characterize the structure, the thermal stability and magnetic properties of Fe₃₆Co₃₆B₁₉Si₅Nb₄ bulk amorphous alloys using XRD, Mössbauer spectroscopy, DSC and VSM methods. Additionally the magnetic permeability μ_i (at force H ≈ 0.5 A/m and frequency f ≈ 1 kHz) and the intensity of disaccommodation of magnetic permeability Δμ/μ(t₁) (Δμ = μ(t₁ = 30 s) ? μ(t₂ = 1800 s)), have been measured, where μ is the initial magnetic permeability measured at time t after demagnetisation, the Curie temperature T_C and coercive force H_c of rods are also determined with the use of a magnetic balance and coercivemeter, respectively.Fe–Co–B–Si–Nb bulk amorphous alloys were produced by pressure die casting with the maximum diameters of 1 mm, 2 mm and 3 mm.The glass transition temperature (T_g) of studied amorphous alloys increases from 807 K for a rod with a diameter of 1 mm to 811 K concerning a sample with a diameter of 3 mm. The crystallization temperature (T_x) has the value of 838 K and 839 K for rods with the diameters of 1 mm and 3 mm, respectively. The supercooled liquid region (ΔT_x = T_x ? T_g) has the value of about 30 K. These values are presumed to be the origin for the achievement of a good glass-forming ability of the Fe–Co–B–Si–Nb bulk amorphous alloy. The investigated amorphous alloys in the form of rods have good soft magnetic properties (e.g. M_s = 1.18–1.24 T). The changes of crystallization temperatures and magnetic properties as a function of the diameter of the rods (time of solidification) have been stated.     

Crystal structure of [NBu4]2[Pd2{C4(COOMe)4}2(μ-OH)2] determined ab initio by charge flipping

The crystal structure of bis(tetra-n-butylammonium)bis(μ₂-hydroxo)-bis(1,2,3,4-tetrakis(methoxycarbonyl)-1,3-butadiene-1,4-diyl)-di-palladium, [NBu₄]₂[Pd₂{C₄(COOMe)₄}₂ (μ-OH)₂], was determined ab initio by X-ray single-crystal diffractometry using the charge flipping method. The compound crystallizes in the monoclinic system with P2₁/c as space group and the following cell parameters: a = 12.8481(6) Å, b = 63.744(3) Å, c = 16.6102(8) Å, β = 111.943(10). The asymmetric unit is formed by two molecules, and the unit cell contains eight molecules (Z = 8) giving a density of 1.369 g cm^?3. The coordination around the Pd(II) atoms is approximately planar, the methoxycarbonyl groups at the α and β positions relative to Pd are perpendicular and parallel to the palladacycle ring, respectively, and the {Pd(μ-O)}₂ core has a bent conformation. The structure closely resembles the features reported previously for other palladacyclopentadiene complexes.     

Decomposition of 8.5 mol.% Y2O3-doped zirconia and its contribution to the degradation of ionic conductivity

Transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy was applied to analyze the microstructure and the local chemical composition of as-sintered and aged Y₂O₃-doped ZrO₂ (YDZ) thick-film substrates with yttria contents of 8.5 mol.% (8YDZ) and 10 mol.% (10YDZ). Selected-area electron diffraction and dark-field TEM imaging show nanoscale precipitates of the tetragonal YDZ phase, which are coherently embedded in grains consisting of the cubic phase. A distinct coarsening of the tetragonal regions is observed after 2500 h annealing of 8YDZ at 950 °C in an oxidizing atmosphere. This coarsening is accompanied by decomposition on the cationic sublattice on the nanoscale, leading to the depletion of yttrium in the tetragonal regions. The decomposition is discussed in terms of spinodal decomposition which takes place even at a high doping concentration of 8.5 mol.% Y₂O₃.     

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.     

Crystal structure and properties of U2Co3Al9

A new ternary compound with stoichiometry U₂Co₃Al₉ has been synthesized. It adopts the orthorhombic Y₂Co₃Ga₉-type structure (space group Cmcm, Z = 4, a = 12.824(2) Å, b = 7.515(1) Å, c = 9.249(2) Å). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θ_CW = −48 K and μ_eff = 3.2 μ_B. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at T_t = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at T_t = 8 K.     

The calculation of electronic parameters of an Ag/chitin/n-Si Schottky barrier diode

We have formed polymeric organic compound chitin film on n-Si substrate by adding a solution of polymeric compound chitin in N,N-dimethylacetamide and lithium chloride on top of an n-Si substrate and then evaporating solvent. It has been seen that the chitin/n-Si contact has 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. The barrier height and ideality factor values of 0.959 eV and 1.553, respectively, for this structure have been obtained from the forward bias I–V characteristics. Furthermore, the energy distribution of the interface state density located in the semiconductor band gap at the chitin/n-Si substrate in the energy range from (E_c − 0.897) to (E_c − 0.574) eV have been determined from the I–V characteristics. The interface state density, N_ss, ranges from 5.965 × 10¹² cm⁻² eV⁻¹ in (E_c − 0.897) eV to 1.706 × 10¹³ cm⁻² eV⁻¹ in (E_c − 0.574) eV and has an exponential rise with bias this energy range.     

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.     

High-temperature thermoelectric properties of Sr2RuYO6 and Sr2RuErO6 double perovskites influenced by structure and microstructure

The high-temperature thermoelectric properties of Sr₂RuYO₆ and Sr₂RuErO₆ double perovskites were evaluated and reported for the first time. These compounds show high Seebeck coefficients not only at room temperature, but also at high temperature (for Sr₂RuYO₆, S_RT ≈ ?475 μV K^?1 and S_1200K ≈ ?250 μV K^?1; Sr₂RuErO₆, S_RT ≈ ?400 μV K^?1 and S_1200K ≈ ?250 μV K^?1). The n-type semiconducting behaviour dominates the resistivity values. Both compounds crystallize in a monoclinic unit cell (space group P2₁/n). The lattice parameters are a = 5.7761(2), b = 5.7804(1), c = 8.1689(1), α = γ = 90° and β = 90.2087(8)° for the Sr₂RuYO₆, and a = 5.7760(1), b = 5.7722(0), c = 8.1544(4), α = γ = 90° and β = 90.2099(7)° for Sr₂RuErO₆. The unit cell can be described approximately as √2a_p × √2a_p × 2a_p, where a_p is the unit cell parameter of the ideal cubic perovskite structure. High-resolution transmission electron microscopy shows an interesting three-dimensional micro-twin-domain texture where the c axis is placed in the three space directions. Structural transitions at high temperatures (T_t(Sr₂RuYO₆) ≈920 K and T_t(Sr₂RuErO₆) ≈890 K) are observed by specific heat measurement in both compounds, which are found to have a strong influence on the Seebeck coefficient and electrical conductivity.