Nanocrystalline TiO2 Electrodes Research Articles

Fabrication of Nanosticks-Like CdS Sensitizer for the Application of Solar Cells.

The novelty of this work is to fabricate the Nanosticks (NSs) like CdS sensitizer on the surface of TiO₂ electrode by chemical bath deposition (CBD) method with a very high vacuum annealed at 350 °C for 30 min. Whereas, nanocrystalline TiO₂ electrodes have been prepared on FTO (SnO₂: F) glass by a spin-coating method with high purity (99.99%, Degussa P25) TiO₂ powder. The surface of the CdS layer has been covered by NSs like structures which are confirmed by the scanning electron microscope image. The 100 nm of platinum-coated FTO substrate and polysulfide-based electrolyte are used to assemble the Grätzel Solar cell (GSC). The performance of solar cell (SC) based on NSs like CdS has been compared with the nanoparticles (NPs) based CdS sensitized SC, where CdS NPs has synthesized by CBD without any post-annealing. The efficiency of NSs like CdS sensitized SC exhibits 2.44%, which is 2 folds of the efficiency of the CdS NPs sensitized SC. The NSs like CdS sensitized SC shows the highest photocurrent 20.24 mA/cm² compared to CdS NPs based SC.

Electrocatalytic CO2 Reduction with a Ruthenium Catalyst in Solution and on Nanocrystalline TiO2.

A RuII complex [Ru(PO3 Et2 -ph-tpy)(6-mbpy)(NCCH3 )]2+ [PO3 Et2 -ph-tpy=diethyl(4-[(2,2':6',2''-terpyridin)-4'-yl]phenyl)phosphonate; 6-mbpy=6-methyl-2,2'-bipyridine] is explored as a molecular catalyst for electrocatalytic CO2 reduction in both a homogeneous solution and, as a phosphonated derivative, on nanocrystalline-TiO2 surfaces. In CH3 CN, the complex acts as a selective electrocatalyst for reduction of CO2 to CO at a low overpotential of 340 mV but with a limited turnover number (TON). An enhancement in reactivity was observed by immobilizing the phosphonated derivative of the catalyst on a nanocrystalline-TiO2 electrode surface, with the catalyst surface protected by a thin overlayer of NiO. The surface-functionalized electrode was characterized by X-ray photoelectron and diffuse reflectance spectroscopies (XPS and DRS). Electrocatalytic reduction of CO2 to CO occurred at -1.65 V versus Fc+/0 with a TON of 237 per catalyst site during 4 h of electrocatalysis. Post-catalysis XPS measurements reveal that the molecular structure of the catalyst is retained on TiO2 after the long-term electrocatalysis.

Pathways Following Electron Injection: Medium Effects and Cross-Surface Electron Transfer in a Ruthenium-Based, Chromophore–Catalyst Assembly on TiO2

Interfacial dynamics following photoexcitation of the water oxidation assembly [((PO3H2)2bpy)2RuII(bpy-bimpy)RuII(tpy)(OH2)]4+, −[RuaII–RubII–OH2]4+, on nanocrystalline TiO2 electrodes, starting from either −[RuaII–RubII–OH2]4+ or −[RuaII–RubIII–OH2]5+, have been investigated. Transient absorption measurements for TiO2–[RuaII–RubII–OH2]4+ in 0.1 M HPF6 or neat trifluoroethanol reveal that electron injection occurs with high efficiency but that hole transfer to the catalyst, which occurs on the electrochemical time scale, is inhibited by local environmental effects. Back electron transfer occurs to the oxidized chromophore on the microsecond time scale. Photoexcitation of the once-oxidized assembly, TiO2–[RuaII–RubIII–OH2]5+, in a variety of media, generates −[RuaIII–RubIII–OH2]6+. The injected electron randomly migrates through the surface oxide structure reducing an unreacted −[RuaII–RubIII–OH2]5+ assembly to −[RuaII–RubII–OH2]4+. In a parallel reaction, −[RuaIII–RubIII–OH2]6+ formed by electron injectio...

Directing the mechanism of CO2 reduction by a Mn catalyst through surface immobilization.

Immobilization of a Mn polypyridyl CO2 reduction electrocatalyst on nanocrystalline TiO2 electrodes yields an active heterogeneous system and also significantly triggers a change in voltammetric and catalytic behaviour, relative to in solution. A combination of spectroelectrochemical techniques are presented here to elucidate the mechanism of the immobilized catalyst in situ.

Enhanced photoelectrochemical properties of nanocrystalline TiO2 electrode by surface sensitization with CuxO quantum dots

Nanoporous anatase TiO2 films were fabricated by a screen-printing method, and CuxO quantum dots (QDs) were deposited on the TiO2 films through successive ionic layer adsorption and reaction (SILAR). The amount of CuxO QDs on the TiO2 films are controlled by changing the number of SILAR cycles. The morphology, microstructure, optical, and photoelectrochemical properties of different CuxO sensitized TiO2 films (CuxO/TiO2) were investigated in detail. The nanoporous TiO2 film offers a large surface area for anchoring QDs. QD deposited samples exhibited a significant improvement in photoelectrochemical performance than the bare of TiO2. CuxO/TiO2, prepared with 7 SILAR cycles, showed the best photoelectrochemical properties, where the photocurrent density was enhanced to 500.01 μA/cm2 compared with 168.88 μA/cm2 of bare TiO2 under visible light. These results indicate that the designed CuxO/TiO2 structure possesses superior charge separation efficiency and photoelectrochemical properties.

Anodized Ti3SiC2 As a Potential Anode Material for Li-Ion Microbatteries

To date, Li-ion microbatteries (µLIBs) are the most in demand storage systems for many microelectronic devices due to their high energy densities and cycling performances1. To enhance their performances beyond the current state of the art, there is an ongoing search to find alternative electrode materials. Recently, the synthesis and electrochemical performance of a new anode material based on MXene2-4, which are fabricated by chemical etching of A element from MAX phases5 (Mn+1AXn: where n = 1, 2, or 3; M is an early transition metal; A is an A-group element; and the X is carbon and/or nitrogen), has been reported. In this work, a fully dense Ti3SiC2 was electrochemically anodized in fluoride containing aqueous electrolyte to produce a thin oxide film based on titania, some silica and carbon. The anodization takes place in a two electrode electrochemical cell in the presence of aqueous electrolyte, 1 M NaOH, 1 M H3PO4, containing 0.1 v/v HF at an applied potential of 10 and 60 V for 3 h. Fig 1. a and b, shows the SEM image of Ti3SiC2 anodized (A-312)at potential of 10 and 60 V, respectively. The morphology and thickness of the porous film formed by the anodization is dependent on the competition between electrochemical oxide formation and chemical dissolution which is strongly affected by the applied potential. At lower applied potential the oxide layer adopt a layered morphology which might due to the selective etching of one of its elements. When the anodizing potential is 60 V, the oxide formation is a dominant process leading to formation of pores. Fig. 1 SEM images of anodized Ti3SiC2 for 3 h at potential of 10 (a) and 60 V (b). Fig. 2a shows the cyclic voltammgram curves obtained for pristine and Ti3SiC2 anodized at 10 and 60 V, recorded at a scan rate of 1 mV.s-1 between 1 – 3 V vs Li/Li+. Unlike the pristine sample, the A-312 exhibits the presence of single cathodic and anodic peaks at 1.67 and 2.17 V vs Li/Li+ corresponding to the insertion and extraction of Li+ in/from anatase titania6. The cycle life performance tests were performed in two electrode Swagelok cell. The half-cells were assembled by using A-312 as a working electrode, Li foil as a counter electrode, and a Whatman glass microfiber soaked in 1 M LiPF6 in EC:DEC electrolyte as separator. The cell was cycled at 200, 300, 500 A.cm-2 in a potential window of 1 – 3 V vs Li/Li+. It delivers a specific capacity of 460, 350, 380 and mAh.cm-2 after 1st, 2nd, and 140th cycles, respectively, Fig2b. The cycle life performance shows a good capacity recovery after being cycled at faster rates. Furthermore, the capacity values are much higher than that reported for amorphous titania nanotubes7, and comparable to that for self-supported titania nanotubes fabricated by Wei and co-workers8. Fig. 2 (a) CVs of pristine material and Ti3SiC2 anodized at 10 and 60 V. (b) Cycling performance of Ti3SiC2 anodized at 60 V at various current density. Reference 1. Ellis, B. L.; Knauth, P.; Djenizian, T., Three-Dimensional Self-Supported Metal Oxides for Advanced Energy Storage. Adv. Mater. 2014, 26 (21), 3368-3397. 2. Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W., Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23 (37), 4248-4253. 3. Come, J.; Naguib, M.; Rozier, P.; Barsoum, M.; Gogotsi, Y.; Taberna, P.-L.; Morcrette, M.; Simon, P., A Non-Aqueous Asymmetric Cell with a Ti2C-Based Two-Dimensional Negative Electrode. J. Electrochem. Soc. 2012, 159 (8), A1368-A1373. 4. Naguib, M.; Halim, J.; Lu, J.; Cook, K. M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W., New Two-Dimensional Niobium and Vanadium Carbides as Promising Materials for Li-ion Batteries. J. Am. Chem. Soc. 2013, 135 (43), 15966-15969. 5. Barsoum, M. W.; El-Raghy, T., The MAX Phases: Unique New Carbide and Nitride Materials-Ternary Ceramics Turn out to Be Surprisingly Soft and Machinable, yet Also Heat-Tolerant, Strong and Lightweight. Am. Sci. 2001, 89 (4), 334-343. 6. Kavan, L.; Grätzel, M.; Rathouský, J.; Zukalb, A., Nanocrystalline TiO2 (Anatase) Electrodes: Surface Morphology, Adsorption, and Electrochemical Properties. J. Electrochem. Soc. 1996, 143 (2), 394-400. 7. Ortiz, G. F.; Hanzu, I.; Djenizian, T.; Lavela, P.; Tirado, J. L.; Knauth, P., Alternative Li-ion Battery Electrode based on Self-Organized Titania Nanotubes. Chem. Mater. 2009, 21 (1), 63-67. 8. Wei, W.; Oltean, G.; Tai, C.-W.; Edstrom, K.; Bjorefors, F.; Nyholm, L., High Energy and Power Density TiO2 Nanotube Electrodes for 3D Li-ion Microbatteries. J. Mater. Chem. A 2013, 1 (28), 8160-8169. Figure 1

(Invited) Development of the Hybrid Solar Cells Using Copper Iodide As a Hole Transport Material

Developing highly efficient and low-cost solar cells as an alternative to conventional silicone solar cell has been attracted much interest. In this regard, the dye-sensitized solar cell (DSC) and perovskite solar cell (PSC) has been intensively studied as a promising system due to its unique operating mechanism to result in reasonably high energy conversion efficiency and its much lower fabrication cost. We have developed a dye-sensitized solid-state cells (DSSCs) using p-CuI or p-CuSCN as a hole-conductor. Although the DSSC is free from the problems associated with the liquid electrolyte, it suffers from its own problems, such as oxidation of CuI under illumination, incomplete pore-filling, loosening of contacts between TiO2 surface and CuI crystallites, and so on. The deposition of CuI inside the voids and on top of the surface of the nanocrystalline TiO2 electrode is achieved by the so called “solution casting” in which the hole conductor (CuI) is dissolved in a suitable solvent and filled into the voids while heating the film to evaporate the solvent. The incomplete pore-filling is a major problem associated with this type of solar cells. Electrodeposition of CuI within the pores of interconnected TiO2 particles has been investigated by the current pulse and continuous current electrodeposition techniques, both in the dark and under illumination. It has been found that the solar cells fabricated using the electrodes prepared by pulse electrodeposition, under illumination, give a collection efficiency of 3.28% with N-719 dye, whereas those prepared by continuous electrodeposition give only 0.75%, both in the absence of triethylamine hydrothiocyanate (THT, a crystal growth inhibiter), under simulated AM 1.5 illumination. CuI films were also grown by the combination of pulse electrodeposition (without THT) followed by solution casting. The cells prepared by these electrodes give even higher collection efficiency of 3.85% compared to 3.38% of the films prepared by only solution casting of CuI in the presence of THT. The major drawback of CuSCN as p-type semiconductor in this solar cell is its poor hole conductivity (10-2 S m-1) and consequent slower rate of reduction of oxidized dye molecules thus allowing the recombination of electrons injected to conduction band of TiO2 with the oxidized dye molecules and/or with holes in CuSCN. We investigated a versatile procedure adopted for significantly enhancing the p-type conductivity of cuprous thiocyanate to result in significantly improved, controllable and tunable performance of the TiO2/N719 Dye/CuSCN all-solid state solar cell. Another approach for DSSCs is focused on TiO2/Sb2S3/CuI/Au-FTO solar cell which utilizes Sb2S3 as an extremely thin light absorbing layer and CuI as a hole conducting material. The solar cell shows very poor performance of lower open-circuit voltage of 0.256 V, a short-circuit current density of 9.50 mA cm-2 and a fill factor of 0.39 under 1 sun illumination for a cell with active surface area of 0.25 cm-2. This is due to the recombination of photo-generated electrons with the holes of the highly conducting CuI. This recombination can be overcome to a certain degree by applying a blocking layer on the Sb2S3 layer to cover the voids in the Sb2S3 layer. The application of N719 dye on the Sb2S3 layer as a recombination blocking layer enhances the conversion efficiency of the solar cell by a factor of 2.5 due to the enhancement of all the solar cell parameters to result in an open circuit voltage of 0.37, short-circuit current density of 13.4 mA cm-2, and a fill factor of 0.50. IPCE and dark current measurements reveal that the main role of the dye on the Sb2S3 layer is the suppression of recombination the electrons with the holes in CuI. Interactions of the NSC groups in the N719 dye with CuI are facilitating the transfer of the photo-generated holes in Sb2S3 to the CuI layer for efficient transport towards the counter electrode. In addition to DSCs, perovskite solar cells (PSCs) have been developed intensively because of rapid increase in its efficiency. PSC has been considered as a kind of derivative of DSCs at first, but recent studies uncovered its unique characteristics different from DSCs. We have also developed PSCs using CuI as a hole transport material. In early studies, application of CuI to PSC gave only poor efficiencies (1-2 %). Recently remarkable improvement has been achieved by introducing carbon nanotube and controlling conditions of CuI film formation. We have successfully fabricated PSCs around 10% of efficiency. The contact between perovskite and CuI seems to play essential role for fabricating efficient PSCs.

A poly (ethylene oxide), poly (vinylidene fluoride) and polycapro lactone polymer blend doped with an indigenous nitrogen–sulfur based organic compound as a novel electrolyte system for dye-sensitized solar cell applications

The present study reports, for the first time, the strategy of blending three different polymers followed by the doping of an organic nitrogenous compound to develop a solvent-free novel doped multi-polymer blend electrolyte system for dye-sensitized solar cell (DSSC) applications. Precisely, this novel electrolyte consists of poly (ethylene oxide) (PEO) blended with poly (vinylidene fluoride) (PVdF) and poly (capro lactone) (PCL) that is incorporated into the synthesized 2,6-bis (2-thio pyridyl) pyridine (BTPP) along with KI and I2. The current–voltage (I–V) characteristics of the nanocrystalline DSSC fabricated using the present electrolyte generates a photocurrent of 15.5mA/cm2, a photo-voltage of 905mV, a fill factor of 0.53 and yields an overall energy conversion efficiency of 9.3% under a simulated sunlight radiation of 80mW/cm2. The impressive photoelectric performance of the fabricated solar cell is mainly attributed to the synergic effects of the electrolyte composed of the unique blending of three polymers and the electron donicity of BTPP that leads to strongly influence the interaction between the nanocrystalline TiO2 electrode and I−/I3− electrolyte, thereby leading to high conversion efficiency.

Atomic layer deposition assisted sacrificial template synthesis of mesoporous TiO2 electrode for high performance lithium ion battery anodes

TiO2 has been considered a promising anode material particularly for large-size Li ion battery (LIB) along with the superior reliability in safety issue. Unfortunately, low Li storage capacity no more than the half of theoretical capacity has been the major bottleneck for the practical utilization of TiO2 anodes. We report mesoporous anatase TiO2 nanocrystalline anode materials produced from atomic layer deposition (ALD) based sacrificial carbon template synthesis for the significant enhancement in reversible capacity approaching the theoretical value. ALD conformal deposition of the nanoscale thick TiO2 layer at sacrificial carbon black template surface and subsequent thermal calcination at relatively low temperature produce mesoporous nanocrystalline TiO2 electrode with anatase crystalline phase. The resultant anode material with large specific surface area (260m2g−1) effectively facilitates the Li intercalation/deintercalation at electrode surface as well as enhances electrolyte permeability. Consequently, remarkable specific capacity (280mAhg−1), high first coulomb efficiency (85%) and excellent cycle ability (80% @100 cycles at 1 C) are achieved (Table S1). This ALD based sacrificial carbon templating method is a fast, facile and controllable advanced technology that offers a robust viable route for various high performance nanostructured materials.

Theoretical Verification of Photoelectrochemical Water Oxidation Using Nanocrystalline TiO2 Electrodes.

Mesoscopic anatase nanocrystalline TiO2 (nc-TiO2) electrodes play effective and efficient catalytic roles in photoelectrochemical (PEC) H2O oxidation under short circuit energy gap excitation conditions. Interfacial molecular orbital structures of (H2O)3 &OH(TiO2)9H as a stationary model under neutral conditions and the radical-cation model of [(H2O)3&OH(TiO2)9H]+ as a working nc-TiO2 model are simulated employing a cluster model OH(TiO2)9H (Yamashita/Jono’s model) and a H2O cluster model of (H2O)3 to examine excellent H2O oxidation on nc-TiO2 electrodes in PEC cells. The stationary model, (H2O)3&OH(TiO2)9H reveals that the model surface provides catalytic H2O binding sites through hydrogen bonding, van der Waals and Coulombic interactions. The working model, [(H2O)3&OH(TiO2)9H]+ discloses to have a very narrow energy gap (0.3 eV) between HOMO and LUMO potentials, proving that PEC nc-TiO2 electrodes become conductive at photo-irradiated working conditions. DFT-simulation of stepwise oxidation of a hydroxide ion cluster model of OH−(H2O)3, proves that successive two-electron oxidation leads to hydroxyl radical clusters, which should give hydrogen peroxide as a precursor of oxygen molecules. Under working bias conditions of PEC cells, nc-TiO2 electrodes are now verified to become conductive by energy gap photo-excitation and the electrode surface provides powerful oxidizing sites for successive H2O oxidation to oxygen via hydrogen peroxide.

Enhanced photovoltaic performance of dye-sensitized solar cells based on NaYF4:Yb3+, Er3+-incorporated nanocrystalline TiO2 electrodes

Near infrared to visible up-conversion of light by rare earth ion-doped phosphors (NaYF4:Yb3+, Er3+) that convert multiple photons of lower energy to higher energy photons offer new possibilities for improved performance of photovoltaic devices. Here, up-conversion phosphor NaYF4:Yb3+, Er3+ doped nanocrystalline TiO2 films are designed and used as a electrode for dye-sensitized solar cells, and the photovoltaic performance of DSSCs based on composite electrodes are investigated. The results show the cell with NaYF4:Yb3+, Er3+ achieves a power conversion efficiency of 7.65% under one sun illumination (AM 1.5G, 100mWcm−2), which is an increase of 14% compared to the cell without NaYF4:Yb3+, Er3+ (6.71%). The performance improvement is attributed to the dual effects of enhanced light harvesting from extended light absorption range and increased light scattering, and lower electron transfer resistance.

Artificial photosynthesis by using chloroplasts from spinach adsorbed on a nanocrystalline TiO2 electrode for photovoltaic conversion

Photovoltaic conversion has been achieved by use of chloroplasts (photosynthetic organs) from spinach adsorbed on a nanocrystalline TiO2 film on an indium tin oxide (ITO) glass electrode (chloroplast/TiO2 electrode). The shape of the absorption spectrum of the chloroplast/TiO2 electrode is almost the same that of a dispersion of the chloroplasts. Absorption maxima of the chloroplast/TiO2 electrode observed at 430, 475, and 670 nm were attributed to carotenoid and chlorophyll molecules, suggesting that chloroplasts have been adsorbed by the nanocrystalline TiO2 film on the ITO electrode. The photocurrent responses of chloroplast/TiO2 electrodes were measured by using a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water and 100 mW cm−2 irradiation. The photocurrent of the chloroplast/TiO2 electrode was increased by adding water to the redox electrolyte. The photocurrent responses of chloroplast/TiO2 electrodes irradiated with monochromatic light (680 nm, the absorption band of photosystem II complexed with evolved oxygen) were measured by use of a solution of 0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile as redox electrolyte in the presence or absence of water. A chloroplast/TiO2 electrode photocurrent was observed only when the redox electrolyte containing water was used, indicating that the oxygen evolved from water by photosystem II in chloroplasts adsorbed by a nanocrystalline TiO2 film on an ITO electrode irradiated at 680 nm is reduced to water by the catalytic activity of the platinum electrode. The maximum incident photon-to-current conversion efficiency (IPCE) was 0.8 % on irradiation at 670 nm.

CdS and CdSe quantum dot co-sensitized nanocrystalline TiO2 electrode: Quantum dot distribution, thickness optimization, and the enhanced photovoltaic performance

The anatase TiO2 nanoparticle films with different thicknesses have been fabricated through screen printing method, and CdS and CdSe quantum dots (QDs) have been deposited on TiO2 films in turn through successive ionic layer adsorption and reaction (SILAR) method. It has been found that the amount of QDs decreases significantly and the size of QDs increases obviously with the depth increasing in TiO2 nanoparticle films, and the size distribution of QDs shifts to large-size direction with the TiO2 film thickness increasing. Furthermore, a qualitative model of CdS/CdSe quantum dot distribution in TiO2 nanoparticle films has been obtained. After optimizing the TiO2 film thickness, the quantum dot-sensitized solar cells (QDSCs) with about 10 μm thick nanocrystalline TiO2 electrodes and Pt counter electrodes have reached relatively high power conversion efficiencies of 3.26 ± 0.10% under one sun illumination (100 mW cm−2, AM 1.5 G).

Influence of microwave plasma pre-treatments of TiO2 electrodes on dye-sensitised solar cell efficiencies

The use of ozone and other pre-treatments of TiO2 photo-electrodes has become an important process step used to increase the efficiency of dye-sensitised solar cells (DSSCs). These pre-treatments are applied to reduce surface contamination and defects in order to improve current density, open circuit voltage and the overall efficiency of DSSCs. This study evaluates the scope of using low pressure microwave (MW) plasma pre-treatments of nanocrystalline TiO2 electrode layers as an alternative pre-treatment method to be applied prior to the dye adsorption step and evaluates the DSSC fabricated using such electrodes. Compared to control cells, (which had not been plasma treated), the power conversion efficiencies of the MW oxygen plasma treated cells exhibited significant improvement, for example up to 23% higher values.When comparing the 30sMW plasma pre-treatment with a 20min, UV-O3 treatment of TiO2 photo-electrodes, the former showed an increase of maximum power density by 23.5% compared to the 14.4% exhibited by the latter. Even though MW plasma treatment is carried out under low pressure (750Pa) compared to the atmospheric pressure UV-O3 treatments, the MW plasma treatment has the additional advantage of a shorter treatment time requiring only 30s instead of the 20min needed for the UV-O3 treatment. The observed improvement in cell efficiencies were shown to have a strong correlation with a decrease in the concentration of oxygen vacancy related Ti3+ defects in TiO2. The cell efficiency decreased with an increase in Ti3+ defects as Ti3+ defects serve as charge recombination centres for back electron transfer pathways. A decrease in Ti3+ concentration also increases the level of dye adsorption as the sensitizers are anchored via Ti4+, again paving the way for improved light harvest and an enhancement in the cell output. These results indicate that the MW plasma treatment represents an alternative rapid method for the pre-treatment of TiO2 photo-electrodes prior to dye adsorption in DSSC manufacturing.

Spectroelectrochemical Photoluminescence of Trap States of Nanocrystalline TiO2 in Aqueous Media

Trap state photoluminescence of nanocrystalline TiO2 electrodes is investigated as a function of applied bias and pH in aqueous electrolyte. Films composed of the anatase polymorph reveal an increase in a broad red emission at increasingly negative potentials, with an onset about 200 mV positive of the pH-dependent literature value of the conduction band potential, followed by conversion to the green emission characteristic of hole traps at more negative bias. Green photoluminescence is the only emission seen from mixed-phase (P25, anatase/rutile) films at any applied potential, while red-emitting electron traps in P25 appear to be quenched by electron transfer to rutile hole traps. The influence of surface treatment by TiCl4 is investigated for both anatase and P25 in order to shed light on the mechanism by which this treatment improves the performance of TiO2-based solar cells. Our results reveal the difference between trap state distributions of P25 and anatase nanoparticles and address the molecular b...

Influences of the electron donor groups on the properties of thiophene-pyrrole-thiophene and tert-butyl based new ruthenium II bipyridyl sensitizers for DSSCs and DFT studies

RuII(4,5-diazafluoren-9-[4-(2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl)]aniline)-(4,4′-dicarboxy-2,2′-bipyridine)(thiocyanate), [Ru(L1)(dcbpy)(NCS)], [K51] and RuII(4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine)-(4,4′-dicarboxy-2,2′-bipyridine)(thiocyanate), [Ru(L2)(dcbpy)(NCS)], [K330] are synthesized as photosensitizers. Photophysical and electrochemical properties are characterized to understand the capabilities of these compounds acting as light sensitizers and injecting electrons to the conduction band of metal-oxide semiconductor. And their photovoltaic properties are investigated in a liquid-state dye sensitized solar cells (DSSCs). A solar energy to electricity conversion efficiencies of 4.92%, 2.52% are obtained under the standard AM 1.5 irradiation (100mWcm−2) with short-circuit photocurrent densities (Jsc) of 17.48mAcm−2 and 7.65mAcm−2, open-circuit photovoltages (Voc) of 506mV and 490mV, and fill factors (ff) of 0.66 and 0.56 for K330 and K51, respectively. As a result, K330 sensitized nanocrystalline TiO2 electrode gives higher efficiency than K51 sensitized nanocrystalline TiO2 electrode in dye sensitized solar cell (DSSC). And also density functional theory studies are carried out to estimate the photovoltaic properties of ruthenium complexes in designed states.

Zinc octacarboxylic phthalocyanine/lutein dyads co-adsorbed nanocrystalline TiO2 electrode: enhancement in photovoltaic performance of dye-sensitized solar cells

A novel zinc phthalocyanine containing eight carboxyl groups was synthesized and utilized as a co-adsorbent with lutein for dye-sensitized solar cells enhance the photoelectric conversion efficiency. The effects of various phthalocyanine/lutein mole ratios on the performances of the fabricated solar cells were investigated. The results showed that zinc octacarboxylic phthalocyanine aggregation decreased with the increasing lutein/phthalocyanine mole ratios and zinc octacarboxylic phthalocyanine fluorescence was strongly quenched due to energy transfer from the phthalocyanine to the excited lutein. The photoelectric conversion efficiency reached its maximum when zinc octacarboxylic phthalocyanine/lutein mole ratio was 4:1. Moreover, the charge-transfer resistances and electron lifetimes at the TiO2/dye/electrolyte interface also showed great dependency on the phthalocyanine/lutein mole ratios by electrochemical impedance spectroscopy. The density-functional theory calculation of zinc phthalocyanine suggests that the electronic cloud density distribution move from the phthalocyanine ring framework toward the anchoring carboxylic group and further to the conduction band of TiO2, which results in efficient electron transfer.

Modification of Mesoporous TiO2 Films by Electrochemical Doping: Impact on Photoelectrocatalytic and Photovoltaic Performance

The effect of reductive electrochemical doping of nanocrystalline TiO2 electrodes on their photoelectrocatalytic properties and their performance in dye-sensitized solar cells is studied. It is observed that accumulation of negative charge (compensated by proton insertion from the supporting electrolyte) leads to a photocurrent increase for water oxidation. Furthermore, an enhanced photoconversion efficiency in dye-sensitized solar cells is observed for the doped electrodes with respect to the unmodified ones. The effect has been analyzed using small-perturbation electrochemical techniques (impedance spectroscopy, intensity-modulated photovoltage, and photocurrent spectroscopy). The results indicate that the better photoelectrocatalytic and photovoltaic efficiency is due to a more rapid electron transport combined with reduced recombination, contributing to improved electron collection. Furthermore, an enhancement in electron injection is also inferred from the analysis of the present results.

3-D solar cells by electrochemical-deposited Se layer as extremely-thin absorber and hole conducting layer on nanocrystalline TiO2 electrode

A three-dimensional selenium solar cell with the structure of Au/Se/porous TiO2/compact TiO2/fluorine-doped tin oxide-coated glass plates was fabricated by an electrochemical deposition method of selenium, which can work for the extremely thin light absorber and the hole-conducting layer. The effect of experimental conditions, such as HCl and H2SeO3 in an electrochemical solution and TiO2 particle size of porous layers, was optimized. This kind of solar cell did not use any buffer layer between an n-type electrode (porous TiO2) and a p-type absorber layer (selenium). The crystallinity of the selenium after annealing at 200°C for 3 min in the air was significantly improved. The cells with a selenium layer deposited at concentrations of HCl = 11.5 mM and H2SeO3 = 20 mM showed the best performance, resulting in 1- to 2-nm thickness of the Se layer, short-circuit photocurrent density of 8.7 mA/cm2, open-circuit voltage of 0.65 V, fill factor of 0.53, and conversion efficiency of 3.0%.

Dye-Sensitized Solar Cells Using Fresh and Dried Natural Dyes

Different natural dye extracts have been prepared and used as sensitizers in the fabrication of dye-sensitized solar cells (DSSCs). These dyes have been extracted from both fresh and dried raw materials. The absorption spectra of these dyes have been investigated by UV-VIS spectrophotometry. DSSCs were assembled using TiO2 and ZnO nanostruc-tured, mesoporous films. Photovoltaic parameters such as short circuit current density Jsc, open circuit voltage Voc, fill fac-tor FF, and overall conversion efficiency η for the fabricated cells were determined under 100 mW/cm2 illumination. The immersion time of the nanocrystalline-TiO2 electrode in spinach extract and the temperature at which this process occurs were optimized. The optimal dying temperature is found to be 60 °C and the efficiency of the DSSC is found to saturate to 0.29% after 12 hr of soaking in the dye solution.