Simple 3,6-bis(diphenylaminyl)carbazole molecular glasses as hole transporting materials for hybrid perovskite solar cells

3,6-bis(diphenylaminyl)carbazole molecular glasses were initially designed as solid hole conductor for solid-state dye-sensitized solar cells. Herein we employed these simple and easy-to-synthesize carbazole derivatives in CH₃NH₃PbI₃ regular perovskite solar cells. Devices using these hole transporting materials (HTM) gave comparable efficiency to the conventional Spiro-OMeTAD based control device made under the same conditions, thus demonstrating the huge potential of carbazole-based molecular glasses as an emerging class of lower cost organic hole conductors with easier synthetic pathways for solid state hybrid solar cells.     

Effect of temperature and α-irradiation on gas permeability for polymeric membrane

In the present study the polyethersulphone (PES) membranes of thickness (35 ±2) μm were prepared by solution cast method. The permeability of these membranes was calculated by varying the temperature and by irradiation of α ions. For the variation of temperature, the gas permeation cell was dipped in a constant temperature water bath in the temperature range from 303–373 K, which is well below the glass transition temperature (498 K). The permeability of H₂ and CO₂ increased with increasing temperature. The PES membrane was exposed by a-source (₉₅Am₂₄₁) of strength (1 μ Ci) in vacuum of the order of 10⁻⁶ torr, with fluence 2.7 × 10⁷ ions/cm². The permeability of H₂ and CO₂ has been observed for irradiated membrane with increasing etching time. The permeability increases with increasing etching time for both gases. There was a sudden change in permeability for both the gases when observed at 18 min etching. At this stage the tracks are visible with optical instrument, which confirms that the pores are generated. Most of pores seen in the micrograph are circular cross-section ones.     

Dielectric properties of Na<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>NbO<Subscript>3</Subscript> in orthorhombic phase

Pellets of ceramic Na_1−xK_xNbO₃ (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and 0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease, and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature with increasing frequency.     

Cadmium substituted high permeability lithium ferrite

Polycrystalline Li_0.5-x/2Cd_xFe_2.5-x/22O₄ ferrites wherex = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 were prepared by a double sintering ceramic technique and characterized by X-ray diffraction and scanning electron microscopy (SEM). The lattice parameter is found to increase monotonically with the cadmium content. It is explained in terms of the sizes of component ions. The grain size of the samples increases up tox = 0.3 and then it decreases for higher values ofx. A similar trend is observed in the variation of Ms with Cd²⁺ content. The initial permeability (μ_i) is however found to increase continuously withx. The increase in μ_i is attributed to decrease of anisotropy constant K₁ and higher grain size of the samples.     

Visible light enhanced TiO2 thin film bilayer dye sensitized solar cells

Visible light enhanced nitrogen-sulfur (N-S) doped titanium dioxide (TiO₂) thin films were prepared by the sol-gel method using thiourea as a dopant. The physical and chemical properties of the TiO₂ thin films were greatly influenced by the amount of thiourea added to the sol-gel solution. The greatest shift to longer wavelengths for visible light absorption was observed with 0.6 g of thiourea in the precursor solution, while 0.4 g yielded the largest particle sizes. These single-cycle dip-deposited N-S doped TiO₂ thin films were used as visible light harvesters as well as blocking layers in dye sensitized solar cells. When deposited directly on conducting fluorine doped tin oxide electrodes, photo-conversion efficiencies were reduced. However, the opposite configuration, with N-S doped thin films on top of nanoporous TiO₂, yielded an increased open-circuit voltage of 0.84 V, a short-circuit current density of 9.86 mA cm⁻², and an overall conversion efficiency of 5.88% greater than that of a standard cell. The effectiveness of the blocking layer on the cell efficiencies was analyzed by electrochemical impedance spectroscopy.     

Metallo-organic compound-based plasma enhanced CVD of ZrO2 films for microelectronic applications

ZrO ₂ films on silicon wafer were deposited by microwave plasma enhanced chemical vapour deposition technique using zirconium tetratert butoxide (ZTB). The structure and composition of the deposited layers were studied by fourier transform infrared spectroscopy (FTIR). The deposition rates were also studied. MOS capacitors fabricated using deposited oxides were used to characterize the electrical properties of ZrO ₂ films. The films showed their suitability for microelectronic applications.     

Dye-sensitized solar cells with natural dyes extracted from rose petals

Nanocrystalline TiO₂ dye-sensitized solar cells have been fabricated using TiO₂ photoelectrode sensitized using the extracts of red rose and table rose as natural sensitizers and their characteristics have been studied. The extracts having anthocyanin pigment (pelargonidin, peonidin and cyanidin), which have hydroxyl and carboxylic groups in the molecule can attach effectively to the surface of TiO₂ film. The solar cell constructed using the red rose sensitized TiO₂ photo-electrode exhibited a short-circuit photocurrent of 4.57 mA/cm² and a power conversion efficiency of 0.81 % and that of table rose sensitized TiO₂ photo-electrode exhibited a short-circuit photocurrent of 4.23 mA/cm² and a power conversion efficiency of 0.67 %. Natural dye sensitized TiO₂ photo electrodes present the prospect to be used as an environment-friendly, low-cost alternative system.     

Preparation of Cu2ZnSnS4 thin films by sulfurization of stacked metallic layers

Stacked precursors of Cu, Sn, and Zn were fabricated on glass/Mo substrates by electron beam evaporation. Six kinds of precursors with different stacking sequences were prepared by sequential evaporation of Cu, Sn, and Zn with substrate heating. The precursors were sulfurized at temperatures of 560 °C for 2 h in an atmosphere of N₂ + sulfur vapor to fabricate Cu₂ZnSnS₄ (CZTS) thin films for solar cells. The sulfurized films exhibited X-ray diffraction peaks attributable to CZTS. Solar cells using CZTS thin films prepared from six kinds of precursors were fabricated. As a result, the solar cell using a CZTS thin film produced by sulfurization of the Mo/Zn/Cu/Sn precursor exhibited an open-circuit voltage of 478 mV, a short-circuit current of 9.78 mA/cm², a fill factor of 0.38, and a conversion efficiency of 1.79%.     

Enhancing photovoltaic performance of photoelectrochemical solar cells with nano-sized ultra thin Sb2S3-sensitized layers in photoactive electrodes

Sb₂S₃-sensitized photoelectrochemical solar cells were prepared with photoactive electrodes containing thick and thin Sb₂S₃-sensitized layers, polyaniline hole conductor containing little amount of de-ionized water, and Pt counter electrodes. The device with the thin Sb₂S₃-sensitized layer shows much higher power conversion efficiency (3.78 %) than that of the device with the thick Sb₂S₃-sensitized layer (0.88 %). The FESEM and TEM images reveal that the device with the thin Sb₂S₃-sensitized layer is nanostructure, as that of the traditional quantum dot sensitized solar cell, while the device with the thick Sb₂S₃-sensitized layer is flat configuration. The photoactive electrode with the thin Sb₂S₃-sensitized layer shows higher light absorption, lower charge transfer resistance and longer electron lifetime compared with that of the one with the thick Sb₂S₃-sensitized layer, which results in higher photocurrent generation of the device.     

Towards an all-polymer cathode for dye sensitized photovoltaic cells

Highly conducting conjugated polymer composite was deposited by vapour phase polymerization. Poly[3,4-ethylenedioxythiophene:para-toluenesulfonate] (PEDOT:PTS) itself was used as the counter electrode in a dye sensitized solar cell. The maximum photocurrent of 9.7 mA/cm², open circuit voltage of 759 mV, fill factor of 0.71 with a power conversion efficiency of 5.25% were observed for glass based wet type dye sensitized solar cell, under illumination of 100 mW/cm². It was observed that the resistance, during operation of the dye sensitized solar cells, due to the I₃⁻ conversion was less with PEDOT:PTS coated cathodes than with standard platinum coated fluorine doped tin oxide and was confirmed by steady state electrochemical measurements.     

High resistivity In-doped ZnTe: electrical and optical properties

Semi-insulating <111> ZnTe prepared by In doping during Bridgman growth was found to have a resistivity of 5.74 × 10⁷ ohm-cm, the highest reported so far in ZnTe, with hole concentration of 2.4 × 10⁹/cm³ and hole mobility of 46 cm² /V.s at 300 K. The optical band gap was 2.06 eV at 293 K compared with 2.26 eV for undoped semiconducting ZnTe. Thermally stimulated current (TSC) studies revealed 2 trap levels at depths of 202–222 meV and 412–419 meV, respectively. Photoluminescence (PL) studies at 10 K showed strong peaks at 1.37 eV and 1.03 eV with a weak shoulder at 1.43 eV. Short anneal for 3 min at 250°C led to conversion to a p-type material with resistivity, 14.5 ohm-cm, indicating metastable behaviour. Raman studies carried out on undoped and In-doped samples showed small but significant differences. Possible models for semi-insulating behaviour and meta-stability are proposed.     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.     

Anatase Mesoporous TiO2 Nanofibers with High Surface Area for Solid‐State Dye‐Sensitized Solar Cells

Mesoporous nanofibers (NFs) with a high surface area of 112 m²/g have been prepared by electrospinning technique. The structures of mesoporous NFs and regular NFs are characterized and compared through scanning electron microscope (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and selected area electron diffraction (SAED) studies. Using mesoporous TiO₂ NFs as the photoelectrode, solid‐state dye‐sensitized solar cells (SDSCs) have been fabricated employing D131 as the sensitizer and P3HT as the hole transporting material to yield an energy conversion efficiency (η) of 1.82%. A J_sc of 3.979 mA cm^?2 is obtained for mesoporous NF‐based devices, which is 3‐fold higher than that (0.973 mA cm^?2) for regular NF‐based devices fabricated under the same condition (η = 0.42%). Incident photon‐to‐current conversion efficiency (IPCE) and dye‐desorption test demonstrate that the increase in J_sc is mainly due to greatly improved dye adsorption for mesoporous NFs as compared to that for regular NFs. In addition, intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) measurements indicate that the mesopores on NF surface have very minor effects on charge transport and collection. Initial aging test proves good stability of the fabricated devices, which indicates the promise of mesoporous NFs as photoelectrode for low‐cost SDSCs.     

Cu2ZnSnS4 thin film solar cells from electroplated precursors: Novel low-cost perspective

Thin-film solar cells based on Cu₂ZnSnS₄ (CZTS) absorbers were fabricated successfully by solid-state reaction in H₂S atmosphere of electrodeposited Cu-Zn-Sn precursors. These ternary alloys were deposited in one step from a cyanide-free alkaline electrolyte containing Cu(II), Zn(II) and Sn(IV) metal salts on Mo-coated glass substrates. The solar cell was completed by a chemical bath-deposited CdS buffer layer and a sputtered i-ZnO/ZnO:Al bilayer. The best solar cell performance was obtained with Cu-poor samples. A total area (0.5 cm²) efficiency of 3.4% is achieved (V_oc = 563 mV, j_sc = 14.8 mA/cm², FF = 41%) with a maximum external quantum efficiency (EQE) of 80%. The estimated band-gap energy from the external quantum efficiency (EQE) measurements is about 1.54 eV. Electron backscatter-diffraction maps of cross-section samples revealed CZTS grain sizes of up to 10 µm. Elemental distribution maps of the CZTS absorber show Zn-rich precipitates, probably ZnS, and a Zn-poor region, presumably Cu₂SnS₃, close to the interface Mo/CZTS.     

Synthesis and characterization of HDA/NaMMT organoclay

In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine (CH₃(CH₂)₁₅NH₂, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5.6 × 10⁻⁴−9.4 × 10⁻³ mmol/l. The rheological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction. The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment with HDA.     

Enhanced efficiency of tri-layered dye solar cells with hydrothermally synthesized titania nanotubes as light scattering outer layer

In the present study dye sensitized solar cells (DSSCs) have been fabricated with a tri-layer photo anode consisting of hydrothermally prepared titania nano tubes (TNT) having a diameter of 9-10 nm and length of several micrometers as outer layer, P25 TiO₂ powder as transparent light absorbing middle layer and a compact TiO₂ inner layer to improve the adhesion of different layers on a transparent conducting oxide coated substrate. In comparison to cells fabricated using TNTs or P25 alone, the tri-layer DSSCs exhibit an enhanced efficiency of 7.15% with a current density of 17.12 mA cm^− 2 under AM 1.5 illumination. The enhancement is attributed to the light scattering generated by TNTs aggregates, reduction in electron transport resistance at the TiO₂/dye/electrolyte interface and an improvement in electron life-time.     

Influence of Zn doping on electrical and optical properties of multilayered tin oxide thin films

In this study, the electrical and optical properties of Zn doped tin oxide films prepared using sol-gel spin coating process have been investigated. The SnO² : Zn multi-coating films were deposited at optimum deposition conditions using a hydroalcoholic solution consisting of stannous chloride and zinc chloride. Films with Zn doping levels from 0–10 wt% in solution are developed. The results of electrical measurements indicate that the sheet resistance of the deposited films increases with increasing Zn doping concentration and several superimposed coatings are necessary to reach expected low sheet resistance. Films with three coatings show minimum sheet resistance of 1–479 kΩ/ in the case of undoped SnO₂ and 77 kΩ/ for 5 wt% Zn doped SnO₂ when coated on glass substrate. In the case of single layer SnO₂ film, absorption edge is 3.57 eV and when doped with Zn absorption edge shifts towards lower energies (longer wavelengths). The absorption edge lies in the range of 3.489-3.557 eV depending upon the Zn doping concentration. The direct and indirect transitions and their dependence on dopant concentration and number of coatings are presented.     

合成介质对PEDOT催化染料敏化太阳电池光阴极性能的影响

采用聚3,4-乙烯二氧噻吩(PEDOT)/FTO为对电极,研究了合成介质对循环伏安法电聚合制备的PEDOT/FTO对电极性能的影响。通过SEM、CV、EIS、Tafel曲线,并首次采用SECM方法对所制备的对电极的电催化性能进行了表征。结果表明:在LiClO4水溶液和1-丁基-3-甲基四氟硼酸盐离子液体(IL)中制备的光阴极具有良好的电催化性能。J-V测试曲线表明,在LiClO4水溶液和IL中制备的光阴极所组装的DSSC器件的光电转化效率分别达6.4%和6.6%,接近于同等条件下以Pt对电极构建的DSSC器件的光电转化效率。     

The optical properties of nanoporous structured titanium dioxide and the photovoltaic efficiency on DSSC

This study examined the characterization of nanoporous structured titanium dioxide and its application to dye-sensitized solar cells (DSSCs). TEM revealed nanopore sizes of 10.0 nm with a regular hexagonal form. When nanoporous structured TiO₂ was applied to DSSC, the energy conversion efficiency was enhanced considerably compared with that using nanometer sized TiO₂ prepared using a hydrothermal method. The energy conversion efficiency of the DSSC prepared from nanoporous structured TiO₂ was approximately 8.71% with the N719 dye under 100 mW cm⁻² simulated light. FT-IR spectroscopy showed that the dye molecules were attached perfectly to the surface and more dye molecules were absorbed on the nanoporous structured TiO₂ than on the nano-sized TiO₂ particles prepared using a conventional hydrothermal method. Electrostatic force microscopy (EFM) showed that the electrons were transferred rapidly to the surface of the nanoporous structured TiO₂ film.     

Fill factor enhancement of organic solar cells based on a wide bandgap phosphorescent material and C60

Planar heterojunction organic solar cells using wide bandgap phosphorescent material bis[2-(4-tertbutylphenyl)benzothiazolato-N,C^2'] iridium (acetylacetonate) [(t-bt)₂Ir(acac)] as electron donor and fullerene (C₆₀) as electron acceptor were fabricated. A large open circuit voltage of 0.94 V was achieved due to low highest occupied molecular orbital level of (t-bt)₂Ir(acac). The effect of different hole transport layers and substrate heating were investigated to improve fill factor. It is shown that the open circuit voltage is strongly influenced by the interface energy barrier, whereas the fill factor is mainly limited by the charge carrier transport properties in active materials. The fill factor was significantly improved by either using hole transport layer with high carrier mobility or increasing the hole mobility of (t-bt)₂Ir(acac). A power conversion efficiency of 2.10% under AM 1.5 solar illumination at an intensity of 100 mW/cm² was achieved by heating the substrate during the deposition of active materials.