Novel zinc porphyrin with phenylenevinylene meso-substituents: Synthesis and application in dye-sensitized solar cells

A novel zinc porphyrin, P, with phenylenevinylene segments at two opposite meso-positions and carboxyphenyl at the other two meso-positions of the porphyrin ring, was synthesized and characterized. The phenylenevinylene substituents were terminated with electron-accepting 4-nitro-α-cyanostilbene units. Elongation of the π-conjugation enhanced the solubility of P as well as broadened and strengthened the absorption spectrum. We have investigated the application of P in quasi solid state dye-sensitized solar cells (DSSCs). Under illumination intensity of 100 mW cm⁻², a power conversion efficiency of 2.90% was obtained for the DSSC based on P as sensitizer, which was significantly improved to 4.22% upon addition of deoxycholic acid (DCA) into the P solution for TiO₂ sensitization. Coadsorption of DCA decreased the dye adsorption, but significantly improved both short circuit current (J_sc) and open circuit voltage (V_oc). The breakup of π stacked aggregates might improve the electron injection yield and thus J_sc. The electrochemical impedance data indicate that the electron lifetime was improved by the coadsorption of DCA, which was attributed to the improvement in both V_oc and J_sc. The increase in J_sc has also been attributed to the reduction of the back reaction i.e., the recombination of electrons with tri-iodide ions.     

Influence of composition and heat treatment in CdCl<Subscript>2</Subscript> solution on intrinsic point defects in CdTe films

CdTe films of different compositions were grown by the chemical molecular-beam deposition method. The activation energy and the nature of deep levels in relation with the composition of films based on the temperature dependence of electroconductivity are defined, and the influence on these levels of heat treatment process in CdCl₂ solution has been studied. Deep levels with the following activation energies are defined: E_v +0.31 eV; E_v + 0.42 ± 0.03 eV; E_c–0.44 ± 0.01 eV; E_c–0.28 eV; E_v + 0.24 ± 0.01 eV.     

Influences of water in bis-benzimidazole-derivative electrolyte additives to the degradation of the dye-sensitized solar cells

The chemical stability of dye-sensitized solar cells (DSSC) determines both the cell performance and the cell life-time. The presence of water in the solar cell from surrounding leakage through the imperfection packaging sealants causes the decrease in life-time of photogenerated electrons on the working electrodes, which induces the occurrence of the dark current to the electrolytes and thus leakage current significantly deteriorated the life-time of the DSSC. Reliable electrolyte additives diminishing the influences of water to the DSSCs degradation process becomes a critical issue in maintaining an acceptable cell life-time.In this work, the effects of four benzimidazole derivatives a-d as the electrolyte additives in the presence of water were comprehensively examined by time-dependent photovoltaic performance of the cells. As a result, open-circuit voltage (V_oc), short-circuit current (J_sc), efficiency (η), and fill factor (FF) collected from I-V curves were studied. In addition, electrochemical impedance spectroscopy (EIS) technique was implemented to evaluate the effects of the charge-transfer resistance (R_ct) at the interfaces between TiO₂/dye/electrolyte. Results showed that the bis-benzimidazole derivative c gives significant improvement in the long-term stability due to the effective protection of the ligands between dye and working electrodes from the attack by environmental water molecules.     

Production and Characteristics of (ZnSe)<Subscript>0.1</Subscript>(SnSe)<Subscript>0.9</Subscript> Films for Use in Thin Film Solar Cells

(ZnSe)_x(SnSe)_1–x films have been produced using chemical molecular beam deposition (CMBD) from an ZnSe and SnSe compound with a stoichiometric composition at a substrate temperature of 500°С. The structural, morphological, and electrophysical properties of (ZnSe)_0.1 (SnSe)_0.9 films are studied. The size of film grains is 5–6 μm. The results of X-ray diffraction analysis of specimens have revealed that the films have a crystalline (orthorhombic) structure. The structural parameters of the produced films are presented. The electrical conductivity of the films measured using the Van der Pauw method varies within 15–0.6 Ω cm^–1.     

Anchorage of N3 dye-linked polyacrylic acid to TiO2/electrolyte interface for improvement in the performance of a dye-sensitized solar cell

A synthetic route was developed to link N3 dye to polyacrylic acid (PAA) using ethylenediamine (en) as the linker. The resulting complex, PAA–en–N3, was then coated onto a TiO₂ film. The modified TiO₂ film electrode (hereafter PAA–en–N3/TiO₂), when used as the photoanode in a dye-sensitized solar cell (DSSC), exhibited enhanced solar energy conversion efficiency compared with that of the usual DSSC with the N3/TiO₂ film electrode. The increase in efficiency was attributed to the increased open-circuit voltage (V_oc) and short-circuit photocurrent (J_sc). The increase in V_oc was attributed to the formation of a hydrophobic PAA–en–N3 layer on the TiO₂/electrolyte interface, while the increase in J_sc was attributed to the additional dye acquired by the TiO₂ film from the PAA–en–N3 complex.     

Thin Semiconductor Films of Fullerene C<Subscript>70</Subscript> Nanoaggregates on the Surface of a Plane Glass Substrate

It was shown for the first time that, in the volume of an evaporating drop of a fullerene C₇₀ solution in toluene located on the surface of a glass substrate, the self-organization of C₇₀ molecules occurs and crystalline nC₇₀ nanoaggregates of a spherical shape are synthesized. Films of nC₇₀ nanoaggregates are deposited on a plane surface of a glass substrate. The physical mechanism of the self-organization of C₇₀ molecules and the formation of large nC₇₀ nanoaggregates are proposed, namely, Ostwald ripening, according to which relatively large nC₇₀ nanoaggregates grow through smaller ones. The possibility of using thin films as solar transducers is discussed.     

Aqueous dye-sensitized solar cell based on new ruthenium diphenyl carbazide complexes

The major challenge of the operation of every solar cell based on dye including water splitting solar cell (WSSC) and dye sensitized solar cell (DSSC) is the using organic solvent medium which causes to decompose the solar cell structure, resulting environmental impact. Here, we synthesized and characterized two new ruthenium complexes with nitrogen and oxygen donor ligands for DSSC application which show good stability on TiO₂ surface in water solvent. Interestingly, the DSSC based on [Ru(dcbpy)₂(DPC)]Cl, where dcbpy = 4,4-dicarboxilic acid 2,2-bipyridin and DPC = diphenylcarbazide, was shown better efficiency in water than methanol dye loading as well as N3 as a benchmark sensitizer in the same condition. The DPC-based exhibited open circuit voltage (V_oc) of 0.63 V, short-circuit current density (J_sc) of 2.5 mA/cm² and fill factor (FF) of 70%, resulting an overall power efficiency of 1.12%. The incident-photon-to-current conversion efficiency (IPCE) value is also reached to 45% for [Ru(dcbpy)₂(DPC)]Cl in the same condition It is proposed that the ruthenium complex containing nitrogen and oxygen donor ligands is more stability on TiO₂ and prevent the decomposition of TiO₂ porous under water solvent condition.     

Novel iminocoumarin dyes as photosensitizers for dye-sensitized solar cell

Novel iminocoumarin dyes (2a-c and 3a-c) having carboxyl and hydroxyl anchoring groups onto the dyes skeletons have been designed and synthesized for the application of dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs). The photophysical and electrochemical studies showed that these iminocoumarin dyes are suitable as light harvesting sensitizers in DSSC application. The dyes having carboxyl and hydroxyl anchoring groups (2a-c) showed better efficiency when compared to the dyes having carboxyl group (3a-c) alone. The cell consisted of dye 2a generated the highest solar-to-electricity conversion efficiency (η) of 0.767% (open circuit voltage (V_oc) = 0.491 V, short circuit photocurrent density (J_sc) = 2.461 mA cm⁻², fill factor (ff) = 0.635) under simulated AM 1.5 irradiation (1000 W m⁻²) with a total semiconductor area of 0.25 cm². The corresponding incident photon-to-current conversion efficiency (IPCE) of the above cell was 21.38%. The overall low efficiency of the dyes is ascribed to the lack of light harvesting ability at longer wavelength region.     

Synthesis of TiO<Subscript>2</Subscript> nanoparticle using sol–gel route and testing its photovoltaic performance in dye-sensitized solar cell

In the present work, sol–gel method is used to synthesize TiO₂ nanoparticle. The characterization of the prepared TiO₂ powder is done using Powder X-ray diffraction (powder XRD), Scanning Electron Microscope (SEM), Energy-Dispersive X-Ray Spectroscopy (EDS) and Ultraviolet-Visible Spectrophotometry (UV-Vis). The XRD pattern reveals formation of anatase phase TiO₂. The SEM images reveal agglomeration of nanoparticles. The absorbance spectrum of TiO₂ nanoparticles was observed with excitonic peaks at 327 nm and the band gap came out to be ~3.2 eV. This prepared TiO₂ was tested for photovoltaic performance by using it in the Dye sensitized solar cell (FTO/TiO₂/N719/KI-I₂/Pt). Conversion of solar light energy to electricity was successfully done using this TiO₂. The fabricated cell showed an open-circuit voltage (V _OC) of 587 mV and short-circuit current density (J _SC) of 5.06 mA/cm². Maximum power (P _max) generated was 1.912 mW/cm² with a fill factor (FF) of 0.644 and a conversion efficiency of 1.91%.     

Enhancement in the performance of dye-sensitized solar cells containing ZnO-covered TiO2 electrodes prepared by thermal chemical vapor deposition

A ZnO-covered TiO₂ (denoted as ZnO/TiO₂) film was prepared by incorporating a small quantity of particulate ZnO in a TiO₂ matrix by thermal chemical vapor deposition. When used in a dye-sensitized solar cell, an enhancement was observed in both short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc) by 12% and 17%, respectively, relative to those of a cell containing a bare TiO₂ film. The observed J_sc enhancement is attributed to the increase in the surface area of the ZnO/TiO₂ film, and the V_oc enhancement to the formation of a potential barrier by ZnO at TiO₂/electrolyte interface. The films were characterized by FE-SEM, EDX, and XRD.     

Synthesis and characterization of trivalent metal porphyrin with NCS ligand for application in dye-sensitized solar cells

Two novel trivalent metal porphyrin dyes, P_Mn-HT-SCN and P_Ga-HT-SCN, were designed, synthesized and firstly applied in dye-sensitized solar cells (DSSCs). These two dyes possess porphyrin donor modified with manganese (III) and gallium (III) as coordination metal and NCS as the second ligand, cyanoacrylic acid as electron-accepting moiety and 4-hexylthiophene as π-spacers. Each of the porphyrin showed different adsorption behavior and saturated coverage on the TiO₂ surface. Between the two dyes, the P_Mn-HT-SCN-based DSSCs afforded the best photovoltaic performance: a short-circuit photocurrent density (J_sc) of 4.32 mA/cm², an open-circuit photovoltage (V_oc) of 0.61 V and a fill factor (FF) of 0.58, corresponding to a solar-to-electricity conversion efficiency of 1.53% under 100 mW/cm² irradiation.     

Solid-state dye-sensitized solar cell with p-type NiO as a hole collector

A solid-state dye-sensitized solar cells (DSSC) comprising of p-type NiO thin layer on TiO₂ was fabricated in which the dye is adsorbed on the p-type oxide and the thin NiO layer acts as a hole collector as well as a barrier for charge recombination. DSSC with NiO-coated TiO₂ electrodes with Ru-dye delivers I_sc=0.15 mA and V_oc=480 mV. It was shown that the p-type oxide materials could be successfully used to construct DSSC and the plausible charge transfer mechanism is discussed.     

Ceramic microfilters based on the solar-furnace-synthesized CaZr<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript>

Ceramic microfilter samples (d _max = 18.3 μm) were prepared based on mixed calcium orthophosphate with an NZP structure melted in a solar furnace; the microfilters have a productivity one order of magnitude higher that that of chamotte-bentonite filters with the same size of the largest pores.     

On the use of triethylamine hydroiodide as a supporting electrolyte in dye-sensitized solar cells

For the first time, the application of a molten salt, triethylamine hydroiodide (THI), as a supporting electrolyte was investigated for the dye-sensitized solar cells (DSSCs). Titanium dioxide (TiO₂) electrode was modified by incorporation of high- and low-molecular weight poly(ethylene glycol) along with TiO₂ nanoparticles of two different sizes (300 nm (30 wt%) and 20 nm (70 wt%)). The highest apparent diffusion coefficient (D) of 8.12×10⁻⁶ cm² s⁻¹ was obtained for I⁻ (0.5 M of THI) from linear sweep voltammetry (LSV). Short-circuit current density (J_sc) increases with the concentration of THI whereas open-circuit potential (V_oc) remains the same. Optimum J_sc (19.28 mA cm⁻²) and V_oc (0.7 V) with a highest conversion efficiency (η) of 8.45% were obtained for the DSSC containing 0.5 M of THI/0.05 M I₂/0.5 M TBP in CH₃CN. It is also observed that the J_sc and η of the DSSC mainly relates with the D values of I⁻ and charge-transfer resistances such as R_ct1 and R_ct2 operating along Pt/TiO₂ electrolyte interface, obtained from LSV and electrochemical impedance spectroscopy (EIS). For comparison, tetraethylammonium iodide (TEAI) and LiI were also selected as supporting electrolytes. Though both the THI and TEAI have similar structures, replacement of one methyl group by hydrogen improves the efficiency of the DSSC containing the former electrolyte. Further, the DSSC containing THI exhibits higher J_sc and η than LiI (7.70%), from which it is concluded that THI may be used as an efficient and alternative candidate to replace LiI in the current research of DSSCs.     

Effects of pH of a hybrid gel incorporated with 3-aminopropyltrimethoxysilane on the performance of a quasi-solid state dye-sensitized solar cell

Network hybrid gel prepared with tetraethyl orthosilicate, 3-aminopropyltrimethoxysilane (APS) and poly(ethylene glycol) was used as an electrolyte matrix in a quasi-solid state dye-sensitized solar cell (DSSC). Change in pH of this hybrid gel by varying the composition of APS was found to have remarkable effects on the photoelectrochemical performance of the cell. The hybrid gel matrix, having silane polymer backbones with free amine functionality, was characterized by FT-IR spectra and FE-SEM images, and the assembled DSSC by photocurrent-voltage and incident photon to current conversion efficiency curves. The unsealed, quasi-solid state DSSC with the hybrid gel has shown an increase in the open-circuit voltage (V_oc) and a steady decrease in the short-circuit photocurrent (J_sc), with increase in the content of APS. A maximum conversion efficiency of 4.5% was obtained for a DSSC by using 20% of APS in its hybrid gel at a light intensity of 100 mW cm⁻². Upon replacing the amino group of APS by bulkier aniline and benzophenoaniline groups, conversion efficiencies of the corresponding DSSCs were reduced. Variations in the V_oc and J_sc are explained in terms of shift of the flat band potential of TiO₂ and a complex formation between I₃⁻ and −NH₂ of APS of the electrolyte.     

On High Dimensional Schrödinger Equation with Quasi-Periodic Potentials

In this paper, we consider the high dimensional Schrödinger equation \( -\frac {d^{2}y}{dt^{2}} + u(t)y= Ey, y\in \mathbb {R}^{n}, \) where u(t) is a real analytic quasi-periodic symmetric matrix, \(E= \text {diag}({\lambda _{1}^{2}}, \ldots , {\lambda _{n}^{2}})\) is a diagonal matrix with λ _j >0,j=1,…,n, being regarded as parameters, and prove that if the basic frequencies of u satisfy a Bruno-Rüssmann’s non-resonant condition, then for most of sufficiently large λ _j ,j=1,…,n, there exist n pairs of conjugate quasi-periodic solutions.     

Studies on polycrystalline cadmium sulphide photoanodes

The spectral dependence of absolute quantum efficiency for chemically deposited cadmium sulphide thin-film electrodes in 1 M NaOH: 0.1 M Na₂S:0.1 M S, is reported. A peak quantum efficiency of 1.75 × 10⁻² is observed at λ = 560 nm. The diffusion length of minority carriers has been calculated from Gartner's photocurrent equation. The light intensity dependence of the short-circuit current (J_sc) was linear, whereas the open-circuit voltage (V_oc) showed a [log I_L]² variation. Reasons for observed low values of V_oc and J_sc are discussed.     

Analysis of turbulence and surface growth models on the estimation of soot level in ethylene non-premixed flames

Soot prediction in a combustion system has become a subject of attention, as many factors influence its accuracy. An accurate temperature prediction will likely yield better soot predictions, since the inception, growth and destruction of the soot are affected by the temperature. This paper reported the study on the influences of turbulence closure and surface growth models on the prediction of soot levels in turbulent flames. The results demonstrated that a substantial distinction was observed in terms of temperature predictions derived using the k-ε and the Reynolds stress models, for the two ethylene flames studied here amongst the four types of surface growth rate model investigated, the assumption of the soot surface growth rate proportional to the particle number density, but independent on the surface area of soot particles, f(A_s) = ρN_s, yields in closest agreement with the radial data. Without any adjustment to the constants in the surface growth term, other approaches where the surface growth directly proportional to the surface area and square root of surface area, f(A_s) = A_s and f(A_s) = √A_s, result in an under-prediction of soot volume fraction. These results suggest that predictions of soot volume fraction are sensitive to the modelling of surface growth.     

Novel symmetric squaraine chromophore containing triphenylamine for solution processed small molecule bulk heterojunction solar cells

New symmetrical low band-gap small molecule materials, SQ-bis[HP-HT2-TPA] and SQ-bis[HP-HT2-BT] incorporating as novel derivative of squaraine-pyrrole framework and π-extended thiophene with triphenyamine (TPA) and benzothiophene (BT) end group, have been synthesized and characterized. The effects of TPA moiety were investigated. Compared to SQ-bis[HP-HT2-BT], SQ-bis[HP-HT2-TPA] exhibited three times improved transporting property of hole carrier and four times enhanced absorptivity by more efficient intermolecular π−π interaction for high-efficiency bulk heterojunction (BHJ) device, suggesting that TPA contributes to a better hole mobility. The bulk-heterojunction photovoltaic devices fabricated with SQ-bis[HP-HT2-TPA]/C₇₁-PCBM BHJ film had an average power-conversion efficiency of 1.83%(±0.12) under 100 mW/cm², with a short-circuit current (J_sc) of 9.32 mA/cm², fill factor (FF) of 0.30, and open-circuit voltage (V_oc) of 0.65 V, which has ∼42% higher efficiency compared to SQ-bis[HP-HT2-BT]/C₇₁-PCBM BHJ films.     

Influence of gamma radiation on spectral photosensitivity of (Si<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> (ZnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solution

Increase of the photosensitivity of the pSi-n(Si₂)_{1 ? x} (ZnSe) _x (0 ≤ x ≤ 0.01) structure exposed to gamma radiation with photon energy E _ph ≥ 2.3 eV has been demonstrated. It is shown that irradiation with dose up to 10⁴ rad raises and radiation with dose up to 10⁵ rad reduces the forward current of the pSi-n(Si₂)_{1 ? x} (ZnSe) _x structure.