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In D-p-A structured organic dyes, rhodanine acetic acid and its derivates have served as electron acceptors successfully. In this work, two single rhodanine organic dyes with different methylene units have been synthesized and applied in dye-sensitized solar cells (DSSCs). The photophysical, electrochemical and photovoltaic properties have been studied systematically. The results show that dye with double methylene units produces a higher photon-to-electron conversion efficiency (eta) of 4.5% than that of a single methylene unit dye with a eta of 4.1%. Also, it is interesting to notice that the lengthened distance between electron acceptor and TiO2 surface does not decrease the short-circuit current density (J(sc)) and IPCE response for both structured dyes. On the contrary, rhodanine dye bearing double methylene units exhibits a better J(sc) and IPCE response than the single methylene unit. The explanation for this trend is probably due to the fact that increased methylene units could suppress regeneration between the injected electron and the oxidized dye effectively., QC 20140130

A novel trigeminal zinc porphyrin sensitizer (T) and two zinc porphyrin monomers (M1 and M2) were successfully designed and synthesized. The spectral, electrochemical, and photovoltaic properties of the porphyrin dyes were investigated. Compared with M1, the molecule of M2 has an additional aliphatic n-hexyloxyl chain at the meso-position of the porphyrin framework, and such a structure is favorable for the formation of a compact hydrophobic layer at the TiO2 surface and the retardation of the diffusion of I-3(-) ions into the nanoporous TiO2 electrode, resulting in more effective suppression of the charge recombination process and a higher V-oc. Meanwhile, M2 has larger IPCE values than those of M1, leading to the higher J(sc) value. Thus, the DSSC devices based on M2 demonstrated a relatively high power conversion efficiency of 5.77%, with the J(sc), V-oc and ff values of 13.93 mA cm(-2), 732 mV, and 0.566, respectively. Even though dye T has the highest molar absorption coefficients and multiple binding moieties, the corresponding power conversion efficiency is 2.30%, which is lower than those for M1 and M2. These observations may be ascribed to the low efficiency of the electron injection process caused by the isolation of the LUMOs from the anchoring carboxyl groups in addition to the lowest adsorption amount., QC 20140404

D-pi-A and D-A-pi-A-structured organic dyes represent different developmental directions of photosensitizers in dye-sensitized solar cells (DSSCs). In this work, two phenothiazine derivatives-based D-pi-A and D-A-pi-A-structured organic dyes have been synthesized and applied in DSSCs. The physical and electrochemical properties of both dyes have been investigated systematically. The results show that the D-A-pi-A-structured dye exhibits a broader spectrum response but lower molar coefficient of extinction when compared to the D-pi-A-structured dye. Regarding photovoltaic performance, the D-pi-A-structured dye yields a higher efficiency (h) of 7.5% with a higher short-circuit current density (J(sc)) of 16.36 mA cm(-2) and open-circuit voltage (V-oc) of 706 mV than that of the D-A-pi-A-structured dye. Incident photon-to-electron conversion efficiency (IPCE) studies and impedance analysis also support these results. These results demonstrate that the phenothiazine derivatives-based D-pi-A-structured organic dyes can compete with, and even exceed, D-A-pi-A-structured organic dyes under the same test conditions., QC 20140804

U ovom radu proučavana je fotokatalitička degradacija arilazo piridonskih boja, 5-(4-supstituisani fenilazo)-6-hidroksi-4-metil-3-cijano-2-piridona, korišćenjem simuliranesunčeve svetlosti. Kao katalizatori korišćeni su komercijalni TiO2 (Aeroxide P25) i TiO2filmovi.U prvom delu rada opisana je sinteza i karakterizacija arilazo piridonskih boja.Arilazo boje su sintetisane na dva načina. Prvi način sinteze obuhvata reakcijediazotovanja supstituisanih anilina i kuplovanja dobijene diazonijum soli sa 6-hidroksi-4-metil-3-cijano-2-piridonom. Drugim načinom arilazo piridonske boje su dobijenekuplovanjem diazonijum soli sa ketoestrom uz ciklizaciju nastalog proizvoda etil 3-okso-2-(supstitisanifenildiazenil)butanoata sa cijanoacetamidom. Da bi se ispitao uticajelektronskih efekata supstituenata na apsorpcione spektre sintetisanih boja, azo-hidrazotautomeriju i konstante kiselosti, sintetisano je jedanaest boja koje su se razlikovale poprirodi supstituenta na fenilnom jezgru diazo komponente. Ovi uticaji su kvantifikovanikorišćenjem Hammett-ove jednačine (princip linearnih korelacija slobodnih energija -LFER princip). Dobijeni rezultati su pokazali da elektron-akceptori prisutni na fenilomjezgru utiču na povećanje π,π-konjugacije u hidrazo tautomeru, dok elektron-donori utiču napovećanje π,π-konjugacije u azo tautomeru. Pokazano je da je elektronsko ponašanjeatoma azota azo i hidrazo grupe različito kod boja sa elektron-donorskim i elektronakceptorskimsupstituentima. Takođe, dobijeni rezultati su pokazali da je udeo hidrazokomponente i konstanta kiselosti najmanji kod nesupstituisanih boja, dok sapovećanjem elektron-donorskih i elektron-akceptorskih svojstava supstituenata u diazokomponenti boja ove vrednosti rastu.U drugom delu rada proučavana je fotokatalitička degradacija arilazo piridonskih bojakorišćenjem komercijalnog katalizatora TiO2, Aeroxide P25. Ispitivan je uticaj sledećihreakcionih parametara na brzinu fotodegradacije 5-(4-sulfofenilazo)-6-hidroksi-4-metil-3-c, In this dissertation photocatalytic degradation of 5-(4-substituted phenylazo)-6-hydroxy-4-methyl-3-cyano-2-pyridone using simulated sun light was investigated. Thecommercial TiO2, Aeroxide P25 and immobilized films were used as photocatalysts.The first part of the dissertation describes synthesis and characterization ofarylazo pyridone dyes. The arylazo pyridone dyes having different substituents (fromelectron-donating to electon-withdrawing) on phenyl ring of diazo component weresynthesized by two ways. The first synthesis way includes diazotization-couplingreactions and involves the conversion of 4-sulphoaniline to the diazonium ionintermediate 4-sulphobenzendiazonium ion, followed by the reaction with 3-cyano-6-hydroxy-4-methyl-2-pyridone. In the second way, the dyes were synthesized bycoupling diazonium salts with ketoesters followed by condensation withcyanoacetamide. The influence of electronic effects of substituents group in the arylazocomponent on the absorption spectra, azo/hydrazo tautomerism and acid constants ofdyes was investigated and quantified using Hammett equation (principle of linear freeenergy relationship-LFER). The obtained results showed that electron-withdrawingsubstituents in the arylazo component increase π,π-conjugation in hydrazo tautomer,while electron-donating substituents increase π,π-conjugation in azo tautomer. In addition, itwas observed that the electronic behaviour of the nitrogen atoms of azo and hydrazo groupis different between derivates with electron-donating and electron-withdrawing substituents.The results also showed that the quantity of hydrazo component and pKa values increasedwith increasing electron-donating and electron-withdrawing efects of substituents.In the second part of the dissertation the photocatalytic degradation of synthesizeddyes using commercial TiO2 Aeroxide P25 was investigated. The influence of differentprocess parameters (catalyst concentration, initial dye concentration, temperature, pH,H2O2 concent

Photon upconversion by sensitized triplet-triplet annihilation (UC-STTA) is a promising strategy for boosting the theoretical maximum efficiency of single threshold solar cells, in particular, dye-sensitized solar cells (DSSCs). Here, we report a substantial increase in the efficiency of UC-STTA on a nanostructured surface, using noncoherent excitation light with intensities as low as 0.5 mW cm(-2), easily achieved under sun illumination. The studied surface was a mesoporous ZrO2 film working as a proxy system for the study of photophysics relevant to DSSCs. A well-known UC-STTA "emitter" dye, 9,10-diphenylanthracene (DPA), was chemically modified to yield methyl 4-(10-p-tolylanthracen-9-yl)benzoate (MTAB), which was chemisorbed onto ZrO2. The "sensitizer" dye, platinum(II) octaethylporphyrin (PtOEP), was free in butyronitrile (BuN) solution surrounding the ZrO2 nanostructure. A rigorous oxygen removal minimized photodegradation of the dyes and enhanced triplet-triplet annihilation efficiency. The system already approaches the so-called "strong annihilation limit" at light intensities below 8 mW cm(-2). Highly efficient triplet-triplet annihilation is a requisite for the use of UC-STTA in DSSCs. Time-resolved data show that the limiting process in the UC-STTA mechanism of the present system is the dynamic triplet energy transfer step from PtOEP in solution to MTAB on the surface of ZrO2. This result can guide the way toward a better understanding and further efficiency improvement of UC-STTA on nanocrystalline metal oxides., QC 20131111

This work investigates the use of different sol–gel routes for fabricating photocatalytic thin TiO2 films on polymeric substrates. Systematic investigation of the sol–gel process was conducted which involved the preparation of TiO2 suspensions by different sol–gel routes, such as: (1) non-aqueous processing (well-controlled hydrolysis rate), (2) alkoxide hydrolysis with excess water + HNO3 + aging at 35°C, (3) sol–gel with excess water + varying HNO3 concentrations (molar ratio of HNO3/Ti = 0.05–1.00) plus refluxing at 80°C, and (4) sol–gel with excess water + HNO3, followed by hydrothermal treatment at 150°C.The major findings are as follows: (1) the first route resulted in amorphous TiO2 with BET surface area close to zero and pore volume which is not detectable, (2) the second and third routes produced nanocrystalline TiO2 with degree of crystallinity of ~30–35% and ~45–55%, respectively, crystallite sizes of ~4.0 nm and ~4.0–5.0 nm, respectively, BET surface area of 170 m2/g and 236 m2/g, respectively, and pore volumes of 0.047 cm3/g and 0.076 cm3/g, respectively, (3) in the case of crystalline TiO2 films, the films with larger BET surface area displayed higher photoactivity, (4) the fourth route produced nanocrystalline TiO2 with degree of crystallinity ~70% and crystallite sizes of ~8.5 nm, (5) the TiO2 samples derived from the non-aqueous sol–gel route and aqueous sol–gel route behaved differently during thermally-induced crystallisation, (6) refluxing at 80°C promotes the crystallisation of TiO2 and the formation of homogeneous TiO2 colloids. The high colloidal homogeneity is a base for suspension stability and results in films of higher porosity and thus higher photoactivity, (7) hydrothermal treatment of TiO2 suspensions resulted in highly crystalline TiO2 with crystallite interfaces; which led to films with optical band-gaps comparable to bulk crystalline TiO2, and high photoactivities, and (8) a nove

Nanocrystalline C-doped TiO2 hybrid hollow spheres were prepared by solvothermal synthesis by controlling calcinations of mixtures of furfural, chitosan or saccharose with titanium isopropoxide. The origin of the carbon influences the texture, the crystalline framework, and the optical and photoelectrochemistry properties of the TiO2. The results indicate that the carbon–TiO2 hybrid hollow spheres may be used as TiO2-based film electrodes for use in solar cells.

In the present paper, we report the synthesis of bimodal mesoporous anatase TiO2 films by the EISA (Evaporation-Induced Self-Assembly) method using sol-gel chemistry combining two porogen agents, a low molecular weight ionic template and a neutral block copolymer. The surfactant template (C(16)mimCl) generates non-oriented worm-like pores (8 to 10 nm) which connect the regularly packed ellipsoidal mesopores (15 to 20 nm diameter) formed by an amphiphilic block copolymer of the type poly(isobutylene)-b-poly(ethylene oxide) (PIB-PEO). The surfactant template can also significantly influence the size and packing of the ellipsoidal mesopores. The mesostructural organization and mesoporosity of the films are studied by Environmental Ellipsometry-Porosimetry (EEP), Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) and electron microscopy techniques. Electrochemical characterization is performed to study the permeability of the films to liquid solutions, using two types of probe moieties (K3FeIII(CN)(6) and Ru(bpy)(3)(2+)) by the wall-jet technique. An optimum ratio of C(16)mimCl/PIB-PEO provides anatase films with a continuous bimodal mesopore structure, possessing a permeability up to two times higher than that of the mesoporous films templated by PIB-PEO only (with partially isolated mesopores). When C(16)mimCl is used in large quantities, up to 20% weight vs. PIB-PEO, large overall porous volume and surface area are obtained, but the mesostructure is increasingly disrupted, leading to a severe loss of permeability of the bimodal films. A dye-sensitized solar cell set-up is used with anatase films as the photoelectrode. The photosensitizer loading and the total energy conversion efficiency of the solar cells using the mesoporous films templated by an optimal ratio of the two porogen agents C(16)mimCl and PIB-PEO can be substantially increased in comparison with the solar cells using mesoporous films templated by PIB-PEO only.

Photoinduced molecular rearrangements are important in daily events essential for life such as visual perception and photo-protection of light harvesting complexes in plants. In this study we demonstrate that similar photoarrangements appear in an analogous technological application where the device performance is controlled by chromophores in sensitized anatase TiO2, one of the main components for light-harvesting in dye-sensitized solar cells (DSC). STM reveals that illumination leads to distortions of organic dyes containing conjugated backbones and of cis-bis(isothiocyanate)-bis-(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II)-bis(tetrabutylammonium), known as N719. The dyes were adsorbed in a closed-packed mode on an anatase(101) single crystal surface and imaged in the dark and under white light illumination in an ultra-high vacuum (UHV). STM images of N719 clearly suggest rearrangements caused by rotation of the dye. Conversely, organic dyes rearrange by photoisomerization depending on the number of double bonds, their position in the molecular structure and on the ligand modifications., QC 20120806

Colloidal upconversion (UC) nanocrystals were explored as energy relay materials for dye-sensitized solar cells for the first time. The utilization of colloidal UC nanocrystals was found to significantly enhance the upconversion efficiency and improve the photocurrent of the cells for low infrared irradiation intensity. In addition, it was found that UC nanocrystals of small size favor infiltration into a TiO2 film and bring higher relay efficiency. Finally, we found that UC nanocrystals can serve as a scattering material to increase the light absorption capability of the cells and increase the overall photocurrent of the cells under simulated sunlight irradiation., QC 20120910

A water-soluble organic redox couple (TT-/DTT) and new organic dyes (D45 and D51) have been developed for aqueous dye-sensitized solar cells (DSCs). An optimal efficiency of 3.5% was obtained using the D51 dye and an optimized electrolyte composition. The highest IPCE value obtained was 68% at 460 nm., QC 20130108

In this study, the feasibility of preparing porous TiO2 films on a stainless steel substrate from a hydrothermally prepared colloidal TiO2 solution by the spray pyrolysis technique is presented. The prepared samples were annealed at different temperatures and characterized by the XPS, XRD and SEM techniques, porosimetry and specific surface area measurements. The photocatalytic activities of the resulting films were evaluated by measuring the degradation of an azo pyridone dye, used as model pollutant, under simulated sunlight conditions. The relationships between the structural and morphological characteristics of the TiO2 films and their photoactivity were observed. It was found that the photoactivity was markedly dependent on the annealing temperature. On increasing the calcination temperature from 500 degrees C to 700 degrees C, the crystallite size and the rutile content increased, whereas the specific surface area and the rate of photodegradation decreased. Calcination at 700 degrees C resulted in a completely loss of photoactivity, due to the partial transformation of anatase to rutile phase, the increased crystallite size and decreased specific surface area. Specific activity (per unit of mass and per unit of surface area) was lowered within thicker films, pointing out significance of transport phenomena through porous films (the transport of dye and the transmittance of light as immaterial reagent). Based on the obtained results, the spray pyrolysis method appears to be a good choice for the preparation of photocatalytically active TiO2 films for the removal of dye pollutants.

A modified polysulfide redox couple, [(CH(3))(4)N](2)S/[(CH(3))(4)N](2)S(n), in an organic solvent (3-methoxypropionitrile) was employed in CdS quantum dot (QD)-sensitized solar cells (QDSSCs), and an unprecedented energy conversion efficiency of up to 3.2% was obtained under AM 1.5 G illumination. The QDs were linked to nanoporous TiO(2) via covalent bonds by using thioglycolic acid, and chemical bath deposition in an organic solvent was then used to prepare the QDSSCs, facilitating high wettability and superior penetration capability of the TiO(2) films. A very high fill factor of 0.89 was observed with the optimized QDSSCs., QC 20110913

Redox couples, as one of the crucial components of dye-sensitized solar cells, have been investigated for many years. Due to the many drawbacks of I I(-)/I(3)(-) electrolyte, scientists have paid more attention to seeking other alternative electrolyte systems. Up to now, the best efficiency of iodine-free redox couple-based DSCs, 7.5%, has been achieved by ferrocene/ferrocenium redox couple under AM 1.5G, 100mW cm(-2) light illumination and other redox couples also show the promising future in DSCs. In this feature article, we systematically present three series of iodine-free redox couples including metal-complexes, inorganic and pure organic redox couples, and further compare the different photovoltaic and photophysical properties of these redox couples. As a consequence, the goals of this article are to show the important progress achieved in the redox couples research area of DSCs and analyze the advantages as well as the disadvantages of these redox couples to speed up the further development of iodine-free redox couples in the future., QC 20110808

Charge separation at the dye/titania interface in dye sensitized solar cells is strongly influenced by the thickness and homogeneity of the sensitizing dye layer, as this controls the potential drop across the interface, and the probability of an excited electron being transferred from the dye to the titania. In this study we use atomic force microscopy and the depth profiling method neutral impact collision ion scattering spectroscopy (NICISS) to investigate the thickness and homogeneity of N719 dye adsorbed to titania before and after rinsing with pure acetonitrile. Both experimental methods show that the dye layers are closed but inhomogencous. Inhomogeneity is more pronounced for unrinsed samples., QC 20150716

Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiOx targets with different oxygen contents. The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films., Sp. Iss. SI 464KZ Times Cited:0 Cited References Count:19

TiO2 films have attracted much attention because of their photoactivity and superhydrophilcity. For the superhydrophilicity studies, most research focused mainly on enhancing superhydrophilicity of Ti02 film under UV illumination. A hydrothermal-dip-coating superwetting TiO2 film was synthesised and found to preserve its superhydrophilicity up to 6 months. This non-UV superwetting TI02 film potentially opens an alternative application as bioactive layer for growing hydroxyapatite (HAP) coating, used extensively as prosthetic device medically.In this research, a systematic study was carried out, aiming to understand and optimise the hydrophilicity and superwetting properties of Ti O2 film without UV illumination. The effect of (i) PEG concentration, (ii) film thickness and (iii) agglomerate size of TiO2 on the wettability of TiO2 film was investigated. Although the presence of PEG does affect the porosity of the film, PEG concentration does not play significant role in retaining superhydrophilicity of the film. The evidence from AFM showed that surface roughness is the key parameter to control in order to retain the superhydrophilic wetting and antifogging behavior of the synthesised films, which can be tuned by simple manipulation of the multilayer assembled of TiO2 nanoparticles through varying the film thickness and agglomerate size. A film thickness of (̃˜140nm) yielded the optimum roughness (rms =23nm) for the creation of the best superhydrophilic wetting behavior. Thicker films smoothened the film roughness, and therefore causing detrimental effects on their superhydrophilic wetting properties. Smaller agglomerate size was also found to be important in retaining the roughness film. The photoactivity of the "non UV illuminated"superhydrophilic film was found that be comparable with a Pilkington Activ™ in degrading methyl blue.The growth of Hydroxyapatite (HAP), synthesised via organic-inorganic hybrid method, and the mechanical stability of the HA

Novel organic dyes (C1-1, C1-5 and C2-1) with a tetrahydroquinoline moiety as the electron donor, different thiophene-containing electron spacers and a cyanoacrylic acid moiety as the electron acceptor have been designed and synthesized for the application in dye-sensitized solar cells (DSSCs). An interesting relationship between the dye structures, properties, and the performance of DSSCs based on these tetrahydroquinoline dyes is obtained. Although C2-1 dye, which has a rigid electron spacer, has the narrowest action spectrum among these dyes, it gives the highest solar-to-electricity conversion efficiency (eta) of 4.49% (V-oc = 600 mV, J(sc) = 11.20 mA/cm(2), ff = 0.67) of a DSSC under simulated AM 1.5 irradiation (100 mW/cm(2)). Under the same conditions, the eta value of a DSSC based on N3 dye is 6.16%., QC 20100525

Zinc stannate (Zn2SnO4) particles with 27-nm size were synthesized by hydrothermal treatment. Nanoporous Zn2SnO4 thin films were prepared on conducting glass substrates and used as working electrodes in dye-sensitized solar cells, DSSC. Their behavior was compared with standard TiO2 cells, using (TBA)(2)-cis-Ru(Hdcbpy)(2)(NCS)(2) (known as N719) as a dye and an electrolyte containing 0.7 M LiI and 0.05 M I-2 in 3-methoxypropionitrile. Under the same working conditions, Zn2SnO4 DSSC showed higher open-circuit potential, but their overall efficiency was lower due to their lower incident photon-to-current conversion efficiency. The properties of electrons in DSSC have been studied by measuring their transport time and lifetime by photocurrent and photovoltage transient measurements, respectively. The electron diffusion length is similar in both oxides, demonstrating the possible use of Zn2SnO4 as an electron collector in DSSC applications. On the other hand, photoinduced absorption measurements reveal problems in the electron injection from the dye to Zn2SnO4, owing to the higher position of its conduction band, in agreement with the higher open-circuit potential measured. Zinc stannate will be an interesting mesoporous material for DSSC, provided the use of dyes with a higher position of the LUMO compared to that of N719, as it will permit attaining higher photovoltages without affecting the photocurrent., QC 20100525

Electrical and optical properties of low-temperature, plasma enhanced chemical vapour deposited films of Ti02 have been studied; the source gases were TiCl4 and O2. The amorphous, as-deposited films had a dielectric constant ~33 consistent with their measured density of 3.2 0.2 g cm - . Films deposited using a -41 V substrate bias contained the anatase phase and some rutile as evidenced from infrared spectroscopy and x-ray scattering. Annealing of these films at 600 C resulted in a significant increase in the rutile content of the film., Pub. in the Sem. Science and Technology, v20, p870-875, 2005.

Photoinduced electron transfer from the valence band of nanocrystalline NiO, a p-type semiconductor, to an excited bound dye, coumarin 343, and the subsequent recombination have been measured by femtosecond transient absorbance spectroscopy probing with white light. It was found that both processes are nonexponential. The photoinduced electron transfer from the semiconductor to the excited bound dye has an ultrafast component (similar to 200 fs), which is comparable to the time constants measured for photoinduced electron injection in C343-TiO2 colloid solutions. The process is very efficient and constitutes the main path of deactivation of the excited dye. Back electron transfer is also remarkably fast, with the main part of the recombination process happening with a time constant of similar to 20 ps. Dye-sensitized nanostructured p-type semiconductors are attractive materials due to their potential use as photocathodes in dye-sensitized solar cells and solid electrolytes in solid-state dye-sensitized solar cells. To our knowledge, this is the first time that the photoinduced electron-transfer kinetics of a sensitized p-type semiconductor has been studied., QC 20100525