Enhanced photovoltaic performance of a dye sensitized solar cell with Cu/N Co-doped TiO<Subscript>2</Subscript> nanoparticles

Pure and Copper/Nitrogen (Cu/N)-codoped TiO₂ photoanodes with various Cu concentrations are prepared via sol–gel route for the photoanode application in dye-sensitized solar cells (DSSCs). All the prepared samples are characterized by X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), UV–Vis spectroscopy (UV–VIS) and Electrochemical Impedance Spectroscopy (EIS). Addition of suitable amount of Cu and N content in TiO₂ can alter its optical and electrical properties by extending absorption in the visible region and band gap reduction. The results show that some of the Ti sites are replaced by Cu atoms while O sites are occupied by N atoms. Upon adequate addition of Cu/N could lead to smaller particle size, higher specific surface area, increased dye adsorption and retarded charge carrier recombination. A significant improvement in the power conversion efficiency is observed in case of optimized 0.3 mol% Cu/N-doped TiO₂ nanoparticles (NPs) based DSSC. This optimized 0.3 mol% Cu/N-doped photoanode accomplished a best power conversion efficiency of 11.70% with a short circuit current density of 23.41 mA cm^?2 which is 41% higher than that of the pure TiO₂ photoanode based DSSC (6.82%).     

Structural and optical properties of Eu2O3 coated TiO2 nanoparticles and their application for dye sensitized solar cell

Specialized applications of dye sensitized solar cells (DSSCs) have attracted much attention as an economical substitute to first and second generation solar cells. Surface modification of TiO₂ nanoparticles with high band gap Eu₂O₃ coating has been carried out by chemical precipitation arrested solvothermal method. The characterizations have been done through X-ray diffraction, transmission electron microscopy, diffuse UV–visible, and photoluminescence spectroscopy. Scanning electron microscopy results reveal an increase in surface roughness in case of Eu₂O₃/TiO₂ electrode, which leads to enhancement in the dye loading capability. The synthesized nanoparticles have been employed for the fabrication of DSSCs. Effect of Eu₂O₃ coating on their performance has been studied. Eu₂O₃/TiO₂ electrode provides better surface area for the dye adsorption, which slows down the electron–hole recombination, and thus, improves the DSSC performance. The photocurrent density–voltage (J–V) characteristics reveal that the efficiency of DSSCs fabricated from Eu₂O₃/TiO₂ nanoparticles is 52 % higher than that from bare TiO₂ nanoparticles.     

The effects of co-sensitization in dye-sensitized solar cells

Triazoloisoquinoline-based organic dyestuff was synthesized and used in the fabrication of dye-sensitized solar cells (DSSCs). After co-sensitization with ruthenium complex, triazoloisoquinoline-based organic dyestuff overcomes the deficiency of ruthenium dyestuff absorption in the blue part of the visible spectrum. The incident photon-to-electron conversion efficiency (IPCE) of cis-dithiocyanate-N,N′-bis-(4-carboxylate-4-tetrabutyl ammoniumcarboxylate-2,2′-bipyridine)ruthenium(II) (N719) at shorter wavelength regions (~350–500 nm) is 35 %. After addition of triazoloisoquinoline-based dyestuff for co-sensitization, the IPCE at 350–500 nm increased significantly. This can be attributed to the increased photocurrent of the cells, which improves the dye-sensitized photoelectric conversion efficiency. After optimization of the cells, an energy conversion efficiency of 8.83 % was achieved using an 12 + 4 μm TiO₂ electrode, under simulated solar illumination (AM 1.5G). As a consequence, this low molecular weight organic dyestuff is a promising candidate as a co-adsorbent and co-sensitizer for highly efficient DSSCs.     

Fabrication and properties of meso-macroporous electrodes screen-printed from mesoporous titania nanoparticles for dye-sensitized solar cells

A meso-macroporous TiO₂ film electrode was fabricated by using mesoporous TiO₂ (m-TiO₂) nanoparticles through a screen-printing technique in order to efficiently control the main fabrication step of dye-sensitized solar cells (DSSCs). The qualities of the screen-printed m-TiO₂ films were characterized by means of spectroscopy, electron microscopy, nitrogen adsorption–desorption and photoelectrochemical measurements. Under the optimal paste composition and printing conditions, the DSSC based on the meso-macroporous m-TiO₂ film electrode exhibits an energy conversion efficiency of 4.14%, which is improved by 1.70% in comparison with DSSC made with commercially available nonporous TiO₂ nanoparticles (P25, Degussa) electrode printed with a similar paste composition. The meso-macroporous structure within the m-TiO₂ film is of great benefit to the dye adsorption, light absorption and the electrolyte transportation, and then to the improvement of the overall energy conversion efficiency of DSSC.     

Nanostructured mesoporous Au/TiO2 for photocatalytic degradation of a textile dye: the effect of size similarity of the deposited Au with that of TiO2 pores

Mesoporous Au/TiO₂ nanocomposites with different Au particle size (7.3–11.8 nm) were synthesized via deposition–precipitation method. The synthesized nanocomposites have been characterized by XRD, TEM, XPS, DLS, ICP-OES, N₂ sorpometry, and UV–Vis spectroscopy. Au/TiO₂ showed higher quantum yield and greater photocatalytic efficiency compared to pure TiO₂ under both ultraviolet and sunlight illumination. The increase of the photocatalytic efficiency of TiO₂ upon deposition with gold nanoparticles, Au NPs, is due to the interface electron transfer from Au nanoparticles to TiO₂ under visible light illumination and from TiO₂ to Au nanoparticles under UV illumination. For the first time, the effect of Au particle sizes when it is very similar to the interparticles pores of TiO₂ has been investigated. The highest reaction rate (5.7 × 10^?2 min^?1) and degradation efficiency of Safranin-O (SO) dye (97 %) were observed when the deposited gold nanoparticles are the smallest among the studied samples (sAu/TiO₂). In spite of blocking a high percentage of the TiO₂ pores, the sAu/TiO₂ sample demonstrated a complete degradation of SO dye in 50 min which is more efficient than any other reported catalysts in the literature.     

Effect of polyaniline concentration on the photoconversion efficiency of nano-TiO<Subscript>2</Subscript> based dye sensitized solar cells

Extensive research have been made in improving the dye sensitized solar cells (DSSC) performance by designing, tailoring and enhancing the photoconversion properties of the matrix. The approaches used are material synthesis, dye permutation combinations, use of natural extracts or using several sensitizers. The polymers are also being explored in this regards in their pristine or composite forms. Therefore, in this study an attempt is made to synthesize a mesoporous polyaniline–titanium dioxide (PANI–TiO₂) nanocomposites with one pot synthesis approach at different concentrations of PANI (0.3–0.7 ml). Titanium isopropoxide was used as precursor for TiO₂ with aniline and the material was synthesized at ice bath temperature. Morphological observations showed that the composite is a mesoporous material with tubular structure where TiO₂ particles are seen entrapped in the polymer matrix and found that intercalation can be tailored with PANI concentration. Structural, functional and optical characterization indicate anatase phase of TiO₂, with several functional bands that can help in dye interaction and broad absorption bands within visible region. The photocurrent-voltage response was measured with simulated light and source-meter. It is interesting to note that increasing PANI concentration enhances the mesoporous structure and hence increases the dye loading capacity and photoconductivity of the material. The efficiency increased by about 22 % with addition of 0.5 ml of PANI from 0.3 ml. The proposed study has indicated that such material have the potential to be used for DSSC fabrication with which the device performance can further be increased to a better levels.     

Dye-sensitized solar cells based on multilayered ultrafine TiO2 nanowire photoanodes

A low-temperature hydrothermal method was used to synthesize ultrafine TiO₂ nanowires with the diameter of 4–6 nm. The ultrafine nanowires tend to gather together, forming nanowire bundles. The length of the nanowires is about 1–4 μm, depending on the growth time. Multilayered TiO₂ nanowires with the height more than 10 μm have been synthesized by a multi-step growth process. Furthermore, the dye-sensitized solar cells (DSSCs) are assembled using single-layered, double-layered and triple-layered TiO₂ nanowires as photoanode respectively. The DSSC based on triple-layered TiO₂ nanowires shows the highest power conversion efficiency of 3.96 % among the prepared samples. The relatively high energy conversion efficiency is attributed to the large surface area, which enhances the absorption of dye molecules.     

Ionic liquid-assisted hydrothermal synthesis of TiO2 nanoparticles and its application in photocatalysis

Anatase TiO₂ nanoparticles have been successfully synthesized at 130 °C for 2 days via ionic liquid-assisted hydrothermal method. The obtained products are characterized using various techniques. The X-ray diffraction data reveal that the nanoparticles are anatase TiO₂. FTIR spectrum shows that the presence of ionic liquid and indicates Ti–O–Ti peak at around 398 cm^?1, and the bands at 1500 and 1600 cm^?1 indicates C–H in-plane vibrations and stretching of imidazolium ring. Raman spectroscopy show bands at 142, 393, 513, and 636 cm^?1 reveal crystalline anatase phase. UV–Vis spectroscopy shows the λ _max at 355 nm corresponding to a band gap of 3.49 eV. TEM images reveal that the average diameters of anatase TiO₂ nanoparticles are in the range 50–100 nm. Anatase TiO₂ exhibited excellent photocatalysis for the degradation of organic dye.     

Synthesis of hierarchical nanoparticles-based ZnO spheres for their application as the light blocking layers in dye-sensitized solar cells

Three-dimensional nanoparticles-based ZnO hierarchical spheres (ZnO-HS) with strong light harvesting and dye loading abilities have been fabricated by a simple hydrothermal method in this paper. These ZnO-HS were designed as the overlayer for light blocking and applied to the dye-sensitized solar cells (DSSCs) based on bare ZnO nanoparticles (ZnO-NP) or TiO₂ nanoparticles (TiO₂-NP). The results show that the values of the short-circuit current density (J _sc) and the power conversion efficiency (η) have been heightened up to 12.6 mA cm^?2 and 3.40 % for the ZnO-NP/ZnO-HS double-layered DSSC, far higher than the bare ZnO-NP DSSC. However, another DSSC assembled by the TiO₂-NP/ZnO-HS double-layered film displays an adverse result for the decreasing of J _sc and η even though the ZnO-HS light blocking layer has been established on the TiO₂-NP film. According to the electrochemical impedance data compared between the ZnO-NP/ZnO-HS double-layered and TiO₂-NP/ZnO-HS double-layered DSSC, it is found that the former possesses less possibility for the occurrence of charge recombination and electronic loss, which is responsible for its better photovoltaic response.     

Optical properties of titanium dioxide nanoparticles/3-(2-benzothiazolyl)-7-N,N-diethylaminocoumarin/polymethyl methacrylate composite films

3-(2-benzothiazolyl)-7-N,N-diethylaminocoumarin organic laser dye-polymethyl methacrylate (PMMA) composite films doped with inorganic titanium dioxide (TiO₂) particles are fabricated by spin-coating technique. TiO₂ nanoparticles exhibit a strong influence on optical properties of the organic laser dye/PMMA composite films. The refractive index and absorbance (absorption intensity) of organic laser dye/PMMA composite film with micro- and nanoparticles of TiO₂ are reduced, compared to those without TiO₂ particles. The organic laser dye/PMMA composite film with TiO₂ nanoparticles has the lowest refractive index and absorbance values. Photoluminescence intensities of all systems exhibit a maximum peak around the excitation wavelength, close to that of the organic laser dye, at 450 nm and the minimum around the excitation wavelength of 350 nm. Photoluminescence intensity of the organic laser dye/PMMA composite film with TiO₂ microparticles is always the lowest at all excitation wavelengths. However, the photoluminescence intensity of the organic laser dye/PMMA composite film with TiO₂ nanoparticles has the highest value at excitation wavelengths of 330 and 380 nm, while the photoluminescence intensity of composite film without TiO₂ particles is more than that with nanoparticles at other excitation wavelengths.     

Study on CaCO3-coated ZnO nanoparticles based dye sensitized solar cell

Dye sensitized solar cells (DSSCs) have been fabricated using ZnO and CaCO₃-coated ZnO nanoparticles. The effect of CaCO₃ coating on the performance of DSSC has been investigated. CaCO₃-coated ZnO nanoparticles have been synthesized by hydrothermal method. X-ray diffraction patterns of synthesized nanoparticles reveal that the ZnO and CaCO₃-coated ZnO nanoparticles have respectively wurtzite and rhomb-centred structure and both having hexagonal phase. Transmission electron microscopy study reveal that ZnO and CaCO₃-coated ZnO nanoparticles possess spherical symmetry and have average particle size respectively 6.2 and 6.7 nm. In case of CaCO₃/ZnO nanoparticles, the quenching in photoluminescence emission intensity has been attributed to the decrease in recombination rate of photo-generated electron–hole pairs. UV–Vis absorption spectra, confirms that the electrodes fabricated from the CaCO₃-coated ZnO nanoparticles have higher absorbance that shows their higher dye adsorbing power. The use of CaCO₃ coating has been found to enhance the efficiency of DSSC by over 100 %.     

Photovoltaic performance of TiO<Subscript>2</Subscript> using natural sensitizer extracted from <Emphasis Type="Italic">Phyllanthus Reticulatus</Emphasis>

Phyllanthus reticulatus, a natural sensitizer has been extracted from Karunelli fruit for the fabrication of TiO₂ based DSSCs. The extracted dye shows the visible light optical absorption at a wavelength of around 520 nm. The presence of anthocyanin in the dye extract has been identified by the functional molecular groups such as intermolecular –OH bond, conjugate C=O stretching vibrations using FTIR. A commercial P25 TiO₂ anatase powder has been employed for the fabrication of photoanode on fluorine doped tin oxide (FTO) substrate using Doctor-blade technique. The Platinum (Pt) counter electrode has been prepared using electron beam evaporation technique with a thickness of ~200 nm. To measure the photoconversion efficiency of the stacked DSSCs, the electrodes are assembled into a cell module and illuminated by a light source simulating AM 1.5 with a light intensity of 100 mW/cm². The freshly prepared sensitizer (P. reticulatus pH ~5.5) exhibits the photo-conversion efficiency of 0.19%, while decreasing the pH of the sensitizer (pH ~1.0) enhances the photoconversion efficiency to six times (0.69%) higher than that of fresh one.     

Low-temperature processing of thin films based on rutile TiO2 nanoparticles for UV photocatalysis and bacteria inactivation

Using a low-temperature, simple, and economic processing technique, TiO₂ nanoparticles (rutile phase) are immobilized in an inorganic matrix and then deposited on glass for bacteria inactivation in water. Using this low thermal budget method (maximum processing temperature of 220 °C), thin films of immobilized TiO₂ nanoparticles are obtained so that practical water decontamination after UV radiation is possible by avoiding the additional step of catalyst separation from treated water. In order to validate the photocatalytic activities of these TiO₂ nanoparticles (prepared as thin films), they were tested for bacteria inactivation in water under UV–A radiation (λ > 365 nm), while extensive characterizations by dynamic light scattering, X-ray diffraction, ultra violet–visible absorption spectroscopy, fourier-transform infra red spectroscopy, and profilometry were also carried out. Despite previous reports on the low or lack of photocatalytic activity of rutile-phase TiO₂, inactivation of Escherichia coli in water was observed when thin films of this material were used when compared with the application of UV radiation alone. Physical characterization of the films suggests that size and concentration-related effects may allow the existence of photocatalytic activity for rutile-TiO₂ as long as they are exposed under UV–A radiation, whereas no effect on bacteria inactivation was observed for thin films in the absence of TiO₂ or radiation. In brief, a low thermal budget process applied to thin films based on TiO₂ nanoparticles has shown to be useful for bacteria inactivation, while possible application of these films on widely available substrates like polyethylene terephthalate materials is expected.     

Preparation and characterization of (100 − x) TiO<Subscript>2</Subscript> + (x)ZnO nanocomposites for dye-sensitized solar cells using <Emphasis Type="Italic">Beta vulgaris</Emphasis> and <Emphasis Type="Italic">Syzygium cumini</Emphasis> natural dye extract

The present paper attempts to report the preparation of TiO₂–ZnO nanocomposite photoanode materials for dye-sensitized solar cells (DSSC) and analyse the efficiency of DSSC with natural dyes. The structural and optical characteristics of the composites were studied by transmission electron microscopy, X-ray diffraction, field effective scanning electron microscopy, energy dispersive spectrometry, photoluminescence and absorption spectroscopy. The synthesized nanocomposites formed on FTO substrates are applied as photoanode in a dye-sensitized solar cell (DSC). The natural dyes extracted from Beta vulgaris (Beetroot) and Syzygium cumini (black plum) were used in the fabrication of DSSC. The solar cells’ photovoltaic performance in terms of short-circuit current, open circuit voltage, fill factor and energy conversion efficiency was tested with photocurrent density–voltage measurements. The evolution of the solar cells parameters is explored as a function of the photoanode and type of dye used in DSSC fabrication.The obtained results show that the efficiency of DSSC significantly changes with the addition of ZnO to TiO_2, while the Beta vulgaris dye has evidently shown higher photo sensitized performance compared to Syzygium cumini in the preparation of DSSC.     

Effect of hydrothermal growth temperature on structural and optical properties of TiO2 nanoparticles

TiO₂ nanoparticles have been prepared by hydrothermal method at different temperatures. The X-ray diffraction results showed that anatase TiO₂ nanoparticles with grain size in the range of 7–27 nm has been obtained. HRTEM images show the formation of TiO₂ nanoparticles with grain size ranging from 7 to 26 nm. The Raman spectra exhibited peaks corresponding to the anatase phase of TiO₂. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increasing hydrothermal temperature.     

CeO2 quantum dot functionalized ZnO nanorods photoanode for DSSC applications

Cerium oxide quantum dots (CeO₂ QDs) decorated zinc oxide nanorods (ZnO NRs) heterostructures were grown by a combination of solvothermal and chemical bath deposition methods and used for dye sensitized solar cell (DSSC) applications. Transmission electron microscope images showed the formation of CeO₂/ZnO NRs, where ~5 nm CeO₂ QDs were decorated on ZnO NRs having 1–2.5 μm length and 100–150 nm width. Photoluminescence spectra showed the significant increase in UV emission after decoration of ZnO NRs with CeO₂ QDs. DSSC results revealed that the ZnO NRs with CeO₂ QDs leads to an increase in the open circuit voltage and fill factor and exhibited a maximum efficiency of 2.65 %, which was 2.01 times higher than that of unmodified ZnO NRs. The decoration of CeO₂ QDs on the ZnO NRs surface may lead to the formation of barrier layer and hindered the back electron transfer and thereby high light harvesting efficiency.     

Dye sensitized solar cell of TiO2 nanoparticle/nanorod composites prepared via low-temperature synthesis in oleic acid

Titania (TiO₂) nanorods (NRs) and nanoparticles (NPs) were synthesized using oleic acid as a surfactant and employed as photoanodes for dye sensitized solar cell (DSSC) fabrication. The synthesized NRs and NPs were characterized using transmission electron microscopy and X-ray diffraction. The photovoltaic performances were compared between NRs, NPs, and their composites. The results showed that the power conversion efficiencies (η) of the composites depend on the relative compositions of NRs and NPs in photoanodes, reaching the greatest at 10% NR content. η of the pure NRs DSSC was lower than that of the NPs DSSC. Electrochemical impedance spectroscopy revealed that the highest η at 10% NRs is mainly due to reduced charge transport resistance at the TiO₂/dye/electrolyte interface and electrolyte diffusion resistance, overcoming the reduction of the number of adsorbed dye molecules.     

Synthesis of cluster like TiO<Subscript>2</Subscript> mesoporous spheres and nanorods and their applications in dye-sensitized solar cells

Cluster like mesoporous TiO₂ spheres, nanorods and nanoparticles were synthesized by simple wet chemical method. The TiO₂ mesoporous spheres, nanorods and nanoparticles were characterized by powder X-ray diffraction, Raman spectroscopy, ultraviolet visible spectroscopy, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. Accordingly, a possible growth mechanism of mesoporous spheres, nanorods and nanoparticles were discussed. The changes of the dye-sensitized solar cell (DSSC) performance with the variation of the nanostructures of TiO₂ which were used in photoanodes have been investigated. The TiO₂ mesoporous sphere based DSSC with the film thickness of 20 μm was assembled and a conversion efficiency of 6.69% was obtained.     

Alkyl and fluoro-alkyl substituted squaraine dyes: A prospective approach towards development of novel NIR sensitizers

Alkyl and fluoroalkyl substituted symmetrical and unsymmetrical squaraine dyes have been synthesized for the fabrication of dye-sensitized solar cells (DSSC) based on nanoporous TiO₂. Results of DSSC performance clearly indicate that introduction of molecular asymmetry and increase in the alkyl chain length of the squaraine sensitizers leads to the enhancement in the photovoltaic performance. A perusal of photo-action spectra of squaraine sensitizer corroborates that introduction of molecular asymmetry and fluoroalkyl substitution leads to hampering of blue-shifted H-aggregate formation. Estimation of energy of HOMO and LUMO for these squaraine sensitizers used in the present investigation indicates that about 0.16 eV is sufficient for electron injection from photoexcited dye to TiO₂ conduction band and dye regeneration.     

The effect of Li intercalation on different sized TiO2 nanoparticles and the performance of dye-sensitized solar cells

The effect of Li⁺ insertion into different sized TiO₂ nanoparticles and their influences on the photoconversion efficiency of dye-sensitized solar cells (DSSC) were investigated. TiO₂ nanoparticles with different particle sizes (22 nm, 14 nm and 6 nm) doped with Li⁺ were employed to form thin film electrodes and their properties were characterized by X-ray diffraction (XRD) and electrochemical impedance spectroscopy analysis. XRD evidenced the presence of anatase as the main phase. From the XRD analysis, it was observed that the Li⁺ ions could be inserted into both the surface and bulk of the TiO₂ nanoparticles. In the larger particle size, the Li⁺ ions are inserted into the bulk anatase where as Li⁺ ions bounded on the TiO₂ surface for the smaller crystallite size. The photovoltaic properties were measured by a current-voltage meter under AM1.5 simulated light radiation. It exhibited that the overall photoconversion efficiency of DSSC was decreased in the larger particles while it was enhanced in the smaller nanoparticles when Li⁺ was doped into the TiO₂ nanoparticles. A nearly 40% decrease in the efficiency (η) of DSSC was observed upon intercalation of Li⁺ ions into 22 nm sized TiO₂ nanoparticles (P25). The 14 nm sized TiO₂ nanoparticles (P90) showed slightly less efficiency (η) upon Li⁺ doping than that of the undoped sample. However, the smallest sized TiO₂ nanoparticles (6 nm) showed higher efficiency than that of the undoped one. This phenomenon is explained based on electron trapping and charge recombination due to lithium doping.