Dye-sensitized TiO2 Solar Cells Research Articles

Effect of Natural Dye Extracts on the Absorbance Characteristics of TiO2 in Dye-Sensitized Solar Cells

Natural dye extracts from Chinese Ixora (Ixora chinensis) flower, Cassod flower (Cassia Siamea), Cassava leaf (Manihot Esculenta), purple heart (Tradescantia Pallida) and Copper leaf (Acalypha Wilkesiana) have been explored as sensitizers for the fabrication of dye-sensitized solar cells. The properties of the dyes were investigated using the FTIR and they all showed broad absorption bands in the 3800 to 3000cm-1 wavelenght and strong presence of intermolecular H-bonds. The effect of dye extracts on the absorbance and transmittance features of TiO2 was well studied by the UV-VIS and the absorbance peak was in the case of sensitization with Manihot Esculenta seen to radically improve above 1.0 at 350nm wavelength. Finally, the current and voltage characteristics of the DSSC were studied in sunlight and at a peak sunlight intensity of 601m/w2, the Manihot and Cassod sensitized devices exhibited maximum voltage values of 115 and 84mV respectively and maximum current values of 4.32 and 2.99mA. These plants have shown great potential for application in fabrication of cost effective and environmentally friendly DSSCs.

High Electronic Coupling between Cu Complexes and Oxidized Dyes Confirmed by Measurements of Driving Force Dependent Regeneration Kinetics in Minimal Electrolyte System.

We confirm fast regeneration kinetics between copper complexes and oxidized organic dyes and the major contribution of electronic coupling (HDA). The highest efficiency of dye-sensitized TiO2 solar cells has been shown by employing Cu complex redox couples. Various groups have reported a fast regeneration rate of oxidized dyes by Cu complexes giving a low driving force attributed to low reorganization energy (λ), but the effect of HDA has not been evaluated. The values of HDA and λ can be derived from driving force dependent transient absorption (TA) measurements. However, analyzing TA decay using Cu complexes is not trivial because accelerated recombination by the presence of Cu2+ complexes and biphasic TA decay often complicates the analysis. Here we employ 16 Cu1+ and Co2+ complexes and two dyes. To simplify the system, i.e., making a minimal electrolyte system, Cu2+ and Co3+ complexes and a common additive of 4-tert-butylpyridine are not used. From the driving force dependent TA decays of oxidized dyes by both Cu1+ and Co2+ complexes, λ for the combination of the Cu complexes and dyes is found to be about 0.15 eV lower than that of Co complexes. Approximately 3 to 5 times higher HDA values of Cu complexes than those of Co complexes are obtained, which is the dominant factor for faster rates. The values vary with the structure of the molecules, showing the possibility of increasing the HDA values further. The higher HDA values of a Cu complex than that of a Co complex are also reproduced by quantum chemical calculations.

Enhancing the Performance of Nanocrystalline TiO2 Dye-Sensitized Solar Cells with Phenothiazine-Doped Blended Solid Polymer Electrolyte

Enhancing the Performance of Nanocrystalline TiO2 Dye-Sensitized Solar Cells with Phenothiazine-Doped Blended Solid Polymer Electrolyte

The Addition of C, Zn-C and Sn-C on Anatase Titanium Dioxide (TiO2) for Dye-Sensitized Solar Cells Application

DSSC (dye-sensitized solar cell) is a third-generation photovoltaic technology that can convert solar energy into electric current using a photoelectrochemical mechanism. Photoelectrode is one of the significant elements in DSSC, where photoexcited electrons are generated, and serves as an electron transport medium. Anatase titanium dioxide (TiO2) is often used as photoelectrode material because of its excellent photoactivity, high stability, non-toxicity, environmental friendliness, and low price. Many DSSC modifications have been conducted to overcome the efficiency limitations in DSSC, and one of them is carried out by modifying the TiO2 via doping. In this study, TiO2 doped with C and co-doping with Zn (Zn-C) and Sn (Sn-C) were prepared using sol-gel reactions, and they were subsequently applied and tested as photoelectrode in DSSC. The results showed that undoped and doped TiO2 had a porous spherical morphology with inhomogeneous particle sizes. The addition of C, Zn-C and Sn-C dopants has reduced in the crystallite size and the band gap energy of TiO2. The efficiency of DSSC with undoped TiO2 DSSC was 3.83%, while the best performance was obtained from DSSC C-TiO2 with an efficiency of 4.20%. In contrast, the DSSC with Zn-C-TiO2 and Sn-C-TiO2 co-doping produced unexpectedly lower efficiency of 0.71% and 0.85%, respectively.

Enhancement of Efficiency of a TiO2-BiFeO3 Dye-Synthesized Solar Cell through Magnetization.

Enhancement in the efficiency of a TiO2 dye-sensitized solar cell (DSSC) has been demonstrated by introducing ferromagnetic perovskite BiFeO3 and controlling the magnetic field, which induces two-dimensional material-like properties in the bulk of the TiO2-BiFeO3 DSSC (a 3-dimensional material). The effect of the concentration of BiFeO3 as well as the magnetization direction on the performance of the TiO2-BiFeO3 DSSC has been investigated. After magnetization, it was confirmed that the current density, efficiency, and open circuit voltage of the TiO2-BiFeO3 DSSC were increased. The observed phenomena have been explained in terms of the Hall effect which is responsible for the reduction of the degree of freedom of the electron movement resulting in the two-dimensional material-like properties in the bulk of the TiO2-BiFeO3 DSSC.

Sterically demanding pyridine-quinoline anchoring ligands as building blocks for copper(I)-based dye-sensitized solar cell (DSSC) complexes.

The Pfitzinger condensation reaction was employed to synthesise N^N sterically demanding ligands bearing carboxylic acid anchoring groups, namely 2,2'-pyridyl-quinoline-4-carboxylic acid (pqca), 6'-methyl-2,2'-pyridyl-quinoline-4-carboxylic acid (6'-Mepqca), 8-methyl-2,2'-pyridyl-quinoline-4-carboxylic acid (8-Mepqca) and 8,6'-dimethyl-2,2'-pyridyl-quinoline-4-carboxylic acid (8,6'-Me2pqca). Preparation of the methyl ester analogues 6'-Mepqcame, 8-Mepqcame and 8,6'-Me2pqcame is also described. All ligands were fully characterised including the X-ray structures of pqca, 6'-Mepqca and 8-Mepqca. We also describe the synthesis and characterisation of seven homoleptic copper(I) complexes of the formula [Cu(N^N)2][PF6] (N^N = pqca (1), 6'-Mepqca (2), 8-Mepqca (3), 8,6'-Me2pqca (4), 6'-Mepqcame (6), 8-Mepqcame (7) and 8,6'-Me2pqcame (8)). Characterisation of the copper(I) complexes includes FT-IR, elemental analyses, multinuclear NMR spectroscopy, UV-vis spectroscopy, cyclic voltammetry, and a single-crystal X-ray diffraction study. The molecular structures of 1·DMSO, 2{2·Me2CO·0.5H2O}, 4, 6·CHCl3·0.13H2O, 2{7·C5H12}·CHCl3 and 8 have been determined, revealing that these complexes adopt a distorted tetrahedral geometry. These are the first crystallographically characterised examples of copper(I)-based coordination compounds incorporating the above mentioned N^N pyridyl-quinoline ligands. In solution, the new complexes are purple to red colored, while 2 displayed excellent stability in acetone at ambient temperature over a month. The absorption spectra of 1-8 display a main broad MLCT band with values of λmax at ∼530 nm and ε values ranging from 1800 to approximately 10 000 dm3 mol-1 cm-1. The photovoltaic performance of the prepared compounds was evaluated on mesoporous nanocrystalline TiO2 dye-sensitized solar cells (DSSCs), and compared with that of the [Cu(dmdcbpy)2][PF6] dye (dmdcbpy = 6,6'-dimethyl-2,2'-bipyridine-4,4'-dicarboxylic acid) (5), that has been used as standard, under the same experimental conditions. From a combination of electrochemical and absorption spectroscopy experiments, the MLCT energy levels of 2 are appropriate for electron injection onto the titania conduction band. Upon optimisation of the semiconductor's architecture, 2 proved to be the most efficient dye, reaching a conversion efficiency of η = 1.20%, which is slightly higher than that of 5 (η = 1.05%), mainly attributed to higher Voc values.

Solvent assisted evolution and growth mechanism of zero to three dimensional ZnO nanostructures for dye sensitized solar cell applications

We report the structural engineering of ZnO nanostructures by a consistent solution method using distinct solvents such as ethylene glycol, 1-butanol, acetic acid and water. The growth kinetics are found to depend strongly on the physicochemical properties of the solvent and zeta potential of the colloidal solution. Furthermore, the resulting nanostructures as a photoanode material, displayed a prominent structure dependent property in determining the efficiency of dye-sensitized solar cells (DSSCs). The fabricated solar cell with ZnO nanostructures based photoanode exhibited improved conversion efficiency. Moreover, the nanoflower based DSSCs showed a higher conversion efficiency of 4.1% compared to the other structures. The excellent performance of ZnO nanoflower is attributed to its better light-harvesting ability and increased resistance to charge-recombination. Therefore ZnO nanostructures can be a promising alternative for TiO2 in DSSCs. These findings provide new insight into the simple, low cost and consistent synthetic strategies for ZnO nanostructures and its outstanding performance as a photoanode material in DSSCs.

Layer-by-Layer Titanium (IV) Chloride Treatment of TiO2 Films to Improve Solar Energy Harvesting in Dye-Sensitized Solar Cells

A layer-by-layer titanium (IV) chloride treatment was applied on different layers of TiO2 in dye-sensitized solar cells (DSSCs). The effects were analysed and compared with standard untreated devices. A significant increase in short-circuit current density (JSC) was observed by employing layer-by-layer TiCl4 treatment of TiO2 in DSSCs. This increase of JSC is attributed to the increased inter-particle connectivity and increase in TiO2 nanoparticle size, resulting in better electron transfer and a lower charge carrier recombination rate. The DSSC fabricated with layer-by-layer-treated TiO2 achieved power conversion efficiency of 8.3%, which is significantly higher than the 6.7% achieved for the DSSC fabricated without TiCl4 treatment. Electrochemical impedance spectroscopy (EIS) was performed to assess the better performance of the device fabricated with TiCl4 treatment. Atomic force microscopy and surface roughness were studied to visualize and statistically determine the function of TiCl4 treatment on different layers of TiO2. Transient photocurrent and transient photovoltage measurements were also performed to gain insight into interfacial charge carrier recombination.

Microwave‐assisted hydrothermal synthesis of Cu‐doped TiO2 nanoparticles for efficient dye‐sensitized solar cell with improved open‐circuit voltage

SummaryAn important reason for the underlying power conversion efficiency (PCE) of the dye sensitized solar cells (DSSCs) is the low open‐circuit voltage (Voc). Considerable efforts have been made to increase the Voc of DSSCs by suppressing charge carrier recombination dynamics, co‐sensitization, and other strategies. Herein, we report an enhancement of the Voc by the incorporation of Cu into TiO2 microstructure via microwave‐assisted hydrothermal synthesis. The prepared nanoparticles and the photoanodes were tested for their efficacy with various structural, optical, and electrical characterization tools. It was found that the incorporation of Cu2+ into TiO2 lattice raises its conduction band (CB) edge and shifted the Fermi level upwards, which contribute towards enhanced Voc. A significant enhancement in Voc from 0.714 to 0.781 V was observed by the Cu incorporation. An optimized 1 wt% Cu modified TiO2 DSSC has shown an efficiency of 6.94% with a high Voc of 0.762 V.

Dye sensitized solar cell (DSC) based on reduced graphene oxide (rGO)-TiO2 nanocomposite photoelectrode and polyaniline (PANI) counter electrode

We report the successful application of reduced graphene oxide–titania (rGO–TiO2) nanocomposite as an efficient photoelectrode and an inexpensive polyaniline (PANI) synthesized by in-situ polymerization on graphite foam as a platinum substitute for tri-iodide reduction for dye‐sensitized solar cell (DSC). The bulk carrier concentration and conductivity of the PANI was measured to be 3.02x1017cm-3 and 4.89x10-1 W-1cm-1 respectively. Subsequently, three DSCs were assembled with rGO–TiO2 nanocomposite photoelectrode and PANI as counter electrode for one and the other two assembled using unmodified TiO2 photoelectrode with PANI and platinum as counter electrodes, respectively. The rGO loading allows more dye to be adsorbed due its large surface area thus improving the light harvesting efficiency (LHE). This improvement in LHE increases the short circuit current density (JSC). The JSC increase is more substantial compared to the reduction in VOC; thus, the increase in the efficiency of the cell with rGO-TiO2 nanocomposite electrode. The short circuit current density for the rGO-TiO2 DSC with PANI counter electrode is 0.45mAcm-2 while that for the unmodified TiO2 DSCs with PANI counter electrode and platinum counter electrode are 0.11mAcm-2 and 0.10 mAcm-2 respectively. This corresponds to 76% increase in the current density and it increases collection rate at the photoelectrode leading to enhanced power conversion efficiency of 0.13% compared with 0.04% and 0.02% for the DSCs assembled with unmodified TiO2 under full sunlight illumination (100 mW/cm2, AM 1.5G) as a result of the better charge collection efficiency of rGO, which reduces the back electron transfer process. This represent 69% enhancement of energy conversion efficiency in the DSC consisting of rGO modified TiO2

Efficient dye-sensitized solar cell based on a new porphyrin complex as an inorganic photosensitizer

The synthesis of new porphyrin complexes that can absorb light in a broad range of the spectrum is very important for getting a high efficiency in dye-sensitized solar cells. The primary reason for using these complexes is good photophysical characteristic like good absorption and high quantum efficiency. Most of the metal porphyrin shows good photophysical characteristics with changing their ligands. In this work, the synthesis of a new Zn-porphyrin complex, that has a good spectral and electrochemical characteristic, is reported. Then, this complex is used as a dye in dye-sensitized solar cells, using titanium dioxide as a semiconductor. The application of this complex in a dye-sensitized nanocrystalline TiO2 solar cell has indicated a short circuit density of 11.60 mA, an open circuit potential of 0.65 V with an overall efficiency of 5.33%. The overall conversion efficiency of this system is due to the efficient electron injection into the conduction band during light absorption. In this work, the synthesis of a new Zn-porphyrin complex, together with its spectral and electrochemical properties, is described. The application of this complex in a dye-sensitized nanocrystalline TiO2 solar cell indicated a short circuit density of 11.60 mA, an open circuit potential of 0.65V with an overall efficiency of 5.33%.

3D Structural Optimization of Zinc Phthalocyanine-Based Sensitizers for Enhancement of Open-Circuit Voltage of Dye-Sensitized Solar Cells

We designed and synthesized two zinc phthalocyanine sensitizers (PcS27 and PcS28), substituted with branched or cyclic alkoxy chains, to investigate the structural effect of peripheral alkyl chains on the performance of dye-sensitized TiO2 solar cells. The bulky cyclic alkyl chains of PcS28 decreased the adsorption density of PcS28 on the TiO2 electrode, while the terminal branches of alkoxy chains of PcS27 did not influence the adsorption density in comparison to the previously published PcS20 with linear alkoxy chains. Under one sun conditions, PcS27 cells exhibited higher open-circuit voltage but a slightly lower energy conversion efficiency, 6.0% less than PcS20. These results suggest that the small alternation of alkoxy chains resulted in decreasing electron pushing ability of peripheral phenoxy units, giving lower short-circuit current.

Aromatic amine passivated TiO2 for dye-sensitized solar cells (DSSC) with ~9.8% efficiency

In this work, the efficiency of dye-sensitized solar cells (DSSC) was improved by capping TiO2 with simple aromatic amines as a complexing agent. The aromatic amines, aniline and o-phenylenediamine capped TiO2 composites were synthesized via hydrothermal route and used as scattering layer in dye-sensitized solar cell (DSSC). Markedly, the maximum photo-conversion efficiency of 9.84% was achieved with o-phenylenediamine capped-TiO2 composite as o-phenylenediamine capped-TiO2 showed higher reflectivity than the pristine TiO2, which is highly beneficial for reflecting the photons back to photoanode. In addition, the average life time of carriers in o-phenylenediamine capped-TiO2 was found to be 9.8 ms, which was 2 times higher than the pristine TiO2 (4.29 ms).

Adsorption and Photovoltaic Properties of Lac-Color on TiO₂ for Dye-Sensitized Solar Cells.

The adsorption and photovoltaic characteristics of Lac-color on TiO₂ thin film for dye-sensitized solar cells were investigated. The adsorption isotherms of Lac-color on TiO₂ thin film could be represented by the Langmuir equation. The adsorption capacity of Lac-color on TiO₂ thin film increased with increasing temperature. The photovoltaic conversion efficiencies of Lac-color increased with increasing amount of dye adsorbed on TiO₂ photo electrode. The energy conversion efficiency of Lac-color was 0.12%.

Increasing the Efficiency of Dye-Sensitized Solar Cells by Adding Nickel Oxide Nanoparticles to Titanium Dioxide Working Electrodes

In this study, nickel oxide (NiO) nanoparticles were added to a titanium dioxide (TiO2) nanoparticle paste to fabricate a dye-sensitized solar cell (DSSC) working electrode by using a screen-printing method. The effects of the NiO proportion in the TiO2 paste on the TiO2 working electrode, DSSC devices, and electron transport characteristics were comprehensively investigated. The results showed that adding NiO nanoparticles to the TiO2 working electrode both inhibited electron transport (a negative effect) and prevented electron recombination with the electrolyte (a positive effect). The electron transit time was extended following an increase in the amount of NiO nanoparticles added, confirming that NiO inhibited electron transport. Furthermore, the energy level difference between TiO2 and NiO generated a potential barrier that prevented the recombination of the electrons in the TiO2 conduction band with the I3- ions in the electrolyte. When the TiO2–NiO ratio was 99:1, the positive effects outweighed the negative effects. Therefore, this ratio was the optimal TiO2–NiO ratio in the electrode for electron transport. The DSSCs with a TiO2–NiO (99:1) working electrode exhibited an optimal power conversion efficiency of 8.39%, which was higher than the DSSCs with a TiO2 working electrode.

Inhibiting Charge Recombination in cis-Ru(NCS)2 Diimine Sensitizers with Aromatic Substituents.

A series of cis-[Ru(LL)(dcbH2)(NCS)2] compounds, where dcbH2 = 2,2'-bipyridine-4,4'-dicarboxylic acid and LL = 1,10-phenanthroline (Ru(phen)), 4,7-dipyrrole-1,10-phenanthroline (Ru(pyr)), 4,7-diindole-1,10-phenanthroline (Ru(ind)), or 4,7-dicarbazole-1,10-phenanthroline (Ru(cbz)), was investigated for application as sensitizers in mesoporous TiO2 dye-sensitized solar cells (DSSCs). A systematic increase in the number of rings of the aromatic substituents at the 4,7-positions of the 1,10-phenanthroline allowed tuning of the molecular size of the sensitizers and the energy stored in the excited state while maintaining the same ground-state Ru3+/2+ reduction potentials. These small structural changes had a significant influence on the rates and/or efficiencies of electron injection, back-electron transfer, recombination to oxidized mediators, lateral self-exchange electron transfer, and regeneration through iodide oxidation that were reflected in distinct photoelectrochemical performance of full operating DSSCs. The global efficiencies, open-circuit voltages, and short-circuit current densities of the DSSCs consistently followed the trend Ru(pyr) < Ru(ind) < Ru(phen) < Ru(cbz), and the most optimal performance of Ru(cbz) was ascribed to dramatically slower recombination to the oxidized redox mediators. Transient photovoltage and transient absorption experiments both revealed significantly slower recombination as the size of the aromatic substituents increased with Ru(cbz) providing the most promising behavior for application in dye sensitization.

Electrospun Nanofiber Mats with Embedded Non-Sintered TiO2 for Dye-Sensitized Solar Cells (DSSCs)

TiO2 is a semiconductor that is commonly used in dye-sensitized solar cells (DSSCs). However, the necessity of sintering the TiO2 layer is usually problematic due to the desired temperatures of typically 500 °C in cells that are prepared on polymeric or textile electrodes. This is why textile-based DSSCs often use metal fibers or metallic woven fabrics as front electrodes on which the TiO2 is coated. Alternatively, several research groups investigate the possibilities to reduce the necessary sintering temperatures by chemical or other pre-treatments of the TiO2. Here, we report on a simple method to avoid the sintering step by using a nanofiber mat as a matrix embedding TiO2 nanoparticles. The TiO2 layer can be dyed with natural dyes, resulting in a similar bathochromic shift of the UV/Vis spectrum, as it is known from sintered TiO2 on glass substrates, which indicates an equivalent chemical bonding. Our results indicate a new possibility for producing textile-based DSSCs with TiO2, even on textile fabrics that are not high-temperature resistant.

Green synthesis of Au and the impact of Au on the efficiency of TiO2 based dye sensitized solar cell

Gold nanoparticles (AuNPs) were prepared through green synthesis route with the aqueous extract from the leaves of Phyllanthus embilica (commonly known as emblic or amla or thoppunelli) without using any surfactant and stabilizer. The synthesized AuNPs colloid was mixed in titanium dioxide slurry to yield Au:TiO2 nanocomposite. The as-synthesized AuNPs and Au:TiO2 nanocomposite were investigated for structural, optical and morphological properties. The dye sensitized solar cells (DSSC) using pure TiO2 and Au:TiO2 nanocomposite photoelectrodes were fabricated and their execution was studied. The efficiency of Au:TiO2 nanocomposite DSSC is improved by about 65% when correlated to the efficiency of the pure TiO2 DSSC. The electrochemical impedance spectroscopic assessment was performed to calculate the transport resistance and lifetime of electron. They decrease in the transport resistance which is accountable for the enhanced electron injection into the photoelectrode was studied using Nyquist plots. The Bode phase plot confirms the lifetime of electron in Au:TiO2 nanocomposite film is greater than that in the pure TiO2 film.

Boosting the efficiency of dye-sensitized TiO2 solar cells using plasmonic gold nanoparticles

Abstract In this work, the focus is on the modification of titanium dioxide (TiO2) photoanode in dye-sensitized solar cells (DSSCs) by mixing the TiO2 with plasmonic gold (Au) nanoparticles with the aim to enhance the performance. Different concentrations of Au nanoparticles were incorporated into TiO2 and their J-V characteristics have been taken under white light intensity of 100 mW cm-2 to obtain the optimum concentration. DSSC made from commercial ruthenium based dye (N3) with TiO2 containing 40 μL Au photoanode and liquid electrolyte (iodolyte Z-50) exhibited the Jsc of 17.52 mA cm-2, Voc of 0.62 V, FF of 0.64 and efficiency, η of 6.97 %. The photovoltaic parameters in terms of Jsc and η have showed improvement by 83% and 68%, respectively. The enhanced performance is due to more photocurrent have been generated as a result from the plasmonic effects of Au nanoparticles that improved the light absorption and scattering.

Influence of synthesized thiourea derivatives as a prolific additive with tris(1,10-phenanthroline)cobalt(II/III)bis/tris(hexafluorophosphate)/ hydroxypropyl cellulose gel polymer electrolytes on dye-sensitized solar cells

An exceptional approach of appending tris(1,10-phenanthroline)cobalt(II)/(III)bis/tris(hexafluorophosphate) and synthesized tetramethyl benzidine-based thiourea derivatives as novel additives with hydroxypropyl cellulose are used to construct a gel polymer electrolyte for DSSC. The thiourea derivatives are synthesized using the cost-effective method. The synthesized derivatives are confirmed by 1H, 13C NMR and mass spectroscopy. The conductivity, surface and redox potential of thiourea derivatives doped Co2+/Co3+ redox electrolytes are scrutinized by impedance spectra, FTIR, UV, XRD. A density functional theory method with full geometry optimization is used to elucidate the adsorption of the symmetrical thiocarbamides on TiO2 (101) surface progressing with electron donating/accepting groups. All the organic compounds display a negative shift on the TiO2 Fermi level simultaneously by adsorption and rebutted as an escalated additive in stable Co(II/III)phen redox electrolyte of the dye-sensitized TiO2 solar cell. This impulse effect influences the sorbate dipole moment component normal to TiO2 surface plane; further, the stable redox mediator and hydroxypropyl cellulose deliver a good performance in a dye-sensitized solar cell. The newly synthesized thiourea derivatives doped Co2+/Co3+ with hydroxypropyl cellulose reports high solar to electric conversion, particularly 1,1'-(3,3′,5,5′-tetramethyl-[1,1′-biphenyl]-4,4′-diyl)bis(3-(3,4,5-trimethoxy phenyl)thiourea) (additive-6) doped redox electrolyte shows an outstanding efficiency (ŋ) of 9.1% under the sunlight irradiation of about 70 mW/cm2.