Photovoltaic Effects of Dye-Sensitized Solar Cells Using Double-Layered TiO2 Photoelectrodes and Pyrazine-Based Photosensitizers

In this study, to obtain high performances of the dye-sensitized solar cells using the optimal TiO₂ photoelectrode for the synthesized pyrazine-based organic photosensitizers, three types of TiO₂ photoelectrodes were fabricated and evaluated for comparison. The double-layered nanoporous TiO₂ photoelectrode (SPD type) consisted of a dispersed TiO₂ layer and a transparent TiO₂ layer. The single-layered nanoporous TiO₂ photoelectrodes (D type and SP type) consisted of a dispersed TiO₂ layer and a transparent TiO₂ layer, respectively. The surface area, pore volume, and crystalline structures of the three types of TiO₂ photoelectrodes were analyzed by Brunauer-Emmett-Teller method, field-emission scanning electron microscopy, and X-ray diffractometry to confirm their crystallinity and surface morphology. The structures of the three types of TiO₂ photoelectrode-adsorbed organic sensitizers were investigated using X-ray photoelectron spectroscopy. The photovoltaic performances of DSSC devices using three organic photosensitizers adsorbed onto the three types of TiO₂ photoelectrodes were investigated under a light intensity of 100 mW/cm² at AM 1.5. The DSSC device using double-layered SPD type TiO₂ photoelectrodes displayed 1.31∼2.64% efficiency, compared to single-layered SP type TiO₂ photoelectrodes (1.31∼2.50%) and D type TiO₂ photoelectrodes (0.90∼1.54%), using organic photosensitizers. The DSSC device using the SPD type TiO₂ photoelectrode and trifluoromethylbenzopyrazine (TPPF) as a photosensitizer showed the highest performances: J _sc of 5.69 mA/cm², V _oc of 0.69 V, FF of 0.67, and efficiency of 2.64%. The relationship between photovoltaic effects and interfacial resistance characteristics of DSSCs using the three organic photosensitizers adsorbed onto the three types of TiO₂ photoelectrodes could be interpreted from interfacial resistances according to frequency through impedance analysis.

Type-II Heterostructure of ZnO and Carbon Dots Demonstrates Enhanced Photoanodic Performance in Photoelectrochemical Water Splitting

Hydrogen evolution through ecofriendly photoelectrochemical (PEC) water splitting is considered to be one of the most cost-effective and desirable methods for meeting ever-growing energy demands. However, the low photoconversion efficiency limits the practical applicability of PEC water splitting. To develop an efficient photoelectrode, here the morphology of ZnO is tuned from 0D to 3D. It is observed that vertically grown 2D nanosheets outperform other morphologies in PEC water splitting by generating nearly 0.414 mA cm^-2 at 0 V vs Ag/AgCl. Furthermore, these perpendicularly developed 2D nanosheets of ZnO are sensitized by metal-free carbon (C) dots to improve the photoconversion efficiency of ZnO. The prepared ZnO/C dots work as an effective photoanode, which can produce a 0.831 mA cm^-2 photocurrent density upon application of 0 V vs Ag/AgCl under constant illumination, which is 2 times higher than that of bare ZnO. The enhanced PEC performance of ZnO/C dots is confirmed by the photoconversion efficiency (η). The ZnO/C dots exhibit a 2-fold-higher photoconversion efficiency (η) compared to that of ZnO. Additionally, the enhancement in PEC activity of ZnO/C dots is attributed to the higher carrier concentrations in the heterostructure. Bare ZnO has a 1.77 × 10²⁰ cm^-3 carrier density, which becomes 3.70 × 10²⁰ cm^-3 after sensitization with C dots. Enhanced carrier density successively leads to higher PEC water splitting efficiency. Band alignments of ZnO and C dots indicate the creation of the type-II heterostructure, which facilitates successful charge transportation among C dots and ZnO, producing a charge-carrier separation. Two-dimensional sheets of ZnO and ZnO/C dots exhibit appreciable stability under continuous illumination for 1 and 2 h, respectively.

Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties

Facile synthesis of Al-doped CaCu₃Ti₄O₁₂ quadruple perovskite has been reported and it is projected to be a promising candidate for Schottky barrier diode application and a methanol steam reforming catalyst for hydrogen generation.

W-doped TiO2 nanoparticles with strong absorption in the NIR-II window for photoacoustic/CT dual-modal imaging and synergistic thermoradiotherapy of tumors

Multifunctional nanomaterials that have integrated diagnostic and therapeutic functions and low toxicity, and can enhance treatment efficacy through combination therapy have drawn tremendous amounts of attention. Herein, a newly developed multifunctional theranostic agent is reported, which is PEGylated W-doped TiO2 (WTO) nanoparticles (NPs) synthesized via a facile organic route, and the results demonstrated strong absorbance of these WTO NPs in the second near-infrared (NIR-II) window due to successful doping with W. These PEGylated WTO NPs can absorb both NIR-II laser and ionizing radiation, rendering them well suited for dual-modal computed tomography/NIR-II photoacoustic imaging and synergistic NIR-II photothermal/radiotherapy of tumors. In addition, the long-term in vivo studies indicated that these PEGylated WTO NPs had no obvious toxicity on mice in vivo, and they can be cleared after a 30-day period. In summary, this multifunctional theranostic agent can absorb both NIR-II laser and ionizing radiation with negligible toxicity and rapid clearance, therefore it has great promise for applications in imaging and therapeutics in biomedicine.

Supramolecular Assembly of a Zn(II)-Based 1D Coordination Polymer through Hydrogen Bonding and π···π Interactions: Crystal Structure and Device Applications

A new mixed-ligand divalent one-dimensional coordination polymer (1D CP) [Zn(adc)(4-nvp)₂(H₂O)₂] _n , (1) [H₂adc = acetylenedicarboxylic acid and 4-nvp = 4-(1-naphthylvinyl)pyridine] has been synthesized and well characterized by elemental analysis, infrared spectrum, single-crystal X-ray crystallography, powder X-ray diffraction pattern, and thermogravimetric analysis. The compound 1 constructs a 3D supramolecular network by the combination of hydrogen bonding, C-H···π, and π···π interactions. Interestingly, the material shows Schottky behavior which is exclusively analyzed with the help of thermionic emission and space charge-limited current theory. In addition, the Schottky barrier diode parameters for compound 1 demonstrate better device performance after light soaking. Hence, the compound has applicability in the fabrication of optoelectronic devices.

Two isostructural linear coordination polymers: the size of the metal ion impacts the electrical conductivity

Electrical conductivity was tuned by altering the metal ions in acetylenedicarboxylate (adc) and 4-styrylpyridine (4-spy)-based 1D coordination polymers, {[M(adc)(4-spy)₂(H₂O)₂]}_n (M = Zn and Cd).

Growth of hierarchical TiO2 flower-like microspheres/oriented nanosheet arrays on a titanium mesh for flexible dye-sensitized solar cells

A triple-layer TiO₂ (TiO₂-TL) structure was synthesized with an over-layer composed of TiO₂ flower-like microspheres (MSs), a middle layer of nanosheet arrays (NSAs) and an under-layer of compact film (CF) on a titanium (Ti) mesh substrate using a one-step hydrothermal route and used to make a series of flexible dye-sensitized solar cells (DSSCs).

3D Conformal Modification of Electrospun Silk Nanofibers with Nanoscaled ZnO Deposition for Enhanced Photocatalytic Activity

Nanostructured metal oxide materials have drawn great attention because of their enhanced semiconducting, electrical, optical, sensing, and chemical catalyzing properties. The application of metal oxides in biomedicine has recently emerged as a promising field, especially in the format of organic/metal oxide composites. However, the existing methods for fabricating organic/metal oxide materials revealed limitations on the precise control over the deposition of metal oxides and the maintenance of organic nanostructures. Here, we developed an approach for the fabrication of composite materials by depositing metal oxides on the nanostructured organic templates through atomic layer deposition (ALD). With this method, we fabricated a series of silk fibroin/ZnO composites at varied deposition temperatures. The results demonstrated that the ZnO layer had a 3D conformality and hexagonal wurtzite structure, and the deposition thickness was well controlled. The photocatalytic activity of silk/ZnO composites was confirmed by the photodegradation of Rh-B under UV exposure, and the efficiency was found to be temperature dependent. These results demonstrated the successful integration of organic materials with metal oxides through an easy and controllable approach for the development of multifunctional organic/metal oxide biomaterials.

Tailored Synthesis of Porous TiO₂ Nanocubes and Nanoparallelepipeds with Exposed {111} Facets and Mesoscopic Void Space: A Superior Candidate for Efficient Dye-Sensitized Solar Cells

Anatase TiO2 nanocubes and nanoparallelepipeds, with highly reactive {111} facets exposed, were developed for the first time through a modified one pot hydrothermal method, through the hydrolysis of tetrabutyltitanate in the presence of oleylamine as the morphology-controlling capping-agent and using ammonia/hydrofluoric acid for stabilizing the {111} faceted surfaces. These nanocubes/nanoparallelepipeds were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and high angle annular dark-field scanning TEM (HAADF-STEM). Accordingly, a possible growth mechanism for the nanostructures is elucidated. The morphology, surface area and the pore size distribution of the TiO2 nanostructures can be tuned simply by altering the HF and ammonia dosage in the precursor solution. More importantly, optimization of the reaction system leads to the assembly of highly crystalline, high surface area, {111} faceted anatase TiO2 nanocubes/nanoparallelepipeds to form uniform mesoscopic void space. We report the development of a novel double layered photoanode for dye sensitized solar cells (DSSCs) made of highly crystalline, self-assembled faceted TiO2 nanocrystals as upper layer and commercial titania nanoparticles paste as under layer. The bilayered DSSC made from TiO2 nanostructures with exposed {111} facets as upper layer shows a much higher power conversion efficiency (9.60%), than DSSCs fabricated with commercial (P25) titania powder (4.67%) or with anatase TiO2 nanostructures having exposed {101} facets (7.59%) as the upper layer. The improved performance in bilayered DSSC made from TiO2 nanostructures with exposed {111} facets as the upper layer is attributed to high dye adsorption and fast electron transport dynamics owing to the unique structural features of the {111} facets in TiO2. Electrochemical impedance spectroscopy (EIS) measurements conducted on the cells supported these conclusions, which showed that the bilayered DSSC made from TiO2 nanostructures with exposed {111} facets as the upper layer possessed lower charge transfer resistance, higher electron recombination resistance, longer electron lifetime and higher collector efficiency characteristics, compared to DSSCs fabricated with commercial (P25) titania powder or with anatase TiO2 nanostructures having exposed {101} facets as the upper layer.

Doping of TiO2 for sensitized solar cells

This review gives a detailed summary and evaluation of the use of TiO2 doping to improve the performance of dye sensitized solar cells. Doping has a major effect on the band structure and trap states of TiO2, which in turn affect important properties such as the conduction band energy, charge transport, recombination and collection. The defect states of TiO2 are highly dependent on the synthesis method and thus the effect of doping may vary for different synthesis techniques, making it difficult to compare the suitability of different dopants. High-throughput methods may be employed to achieve a rough prediction on the suitability of dopants for a specific synthesis method. It was however found that nearly every employed dopant can be used to increase device performance, indicating that the improvement is not so much caused by the dopant itself, as by the defects it eliminates from TiO2. Furthermore, with the field shifting from dye sensitized solar cells to perovskite solar cells, the role doping can play to further advance this emerging field is also discussed.

Boosting Photovoltaic Performance of Dye-Sensitized Solar Cells Using Silver Nanoparticle-Decorated N,S-Co-Doped-TiO2 Photoanode

A silver nanoparticle-decorated N,S-co-doped TiO₂ nanocomposite was successfully prepared and used as an efficient photoanode in high-performance dye-sensitized solar cells (DSSCs) with N719 dye. The DSSCs assembled with the N,S-TiO₂@Ag-modified photoanode demonstrated an enhanced solar-to-electrical energy conversion efficiency of 8.22%, which was better than that of a DSSC photoanode composed of unmodified TiO₂ (2.57%) under full sunlight illumination (100 mWcm⁻², AM 1.5 G). This enhanced efficiency was mainly attributed to the reduced band gap energy, improved interfacial charge transfer, and retarded charge recombination process. The influence of the Ag content on the overall efficiency was also investigated, and the optimum Ag content with N,S-TiO₂ was found to be 20 wt%. Because of the enhanced solar energy conversion efficiency of the N,S-TiO₂@Ag nanocomposite, it should be considered as a potential photoanode for high-performance DSSCs.

Mesoporous titania-vertical nanorod films with interfacial engineering for high performance dye-sensitized solar cells

Working electrode (WE) fabrication offers significant challenges in terms of achieving high-efficiency dye-sensitized solar cells (DSCs). We have combined the beneficial effects of vertical nanorods grown on conducting glass substrate for charge transport and mesoporous particles for dye loading and have achieved a high photoconversion efficiency of (η) > 11% with an internal quantum efficiency of ∼93% in electrode films of thickness ∼7 ± 0.5 μm. Controlling the interface between the vertical nanorods and the mesoporous film is a crucial step in attaining high η. We identify three parameters, viz., large surface area of nanoparticles, increased light scattering of the nanorod-nanoparticle layer, and superior charge transport of nanorods, that simultaneously contribute to the improved photovoltaic performance of the WE developed.

Facile synthesis of Au@TiO2 nanocomposite and its application as a photoanode in dye-sensitized solar cells

Au@TiO₂ nanocomposite materials were synthesized by a facile one-step chemical reduction method and employed as photoanodes in dye-sensitized solar cells.

Improved supercapacitive charge storage in electrospun niobium doped titania nanowires

Niobium doped titania nanowires showed an order of magnitude higher capacitance than the parent material.

Enhanced photovoltaic performance of silver@titania plasmonic photoanode in dye-sensitized solar cells

Ag@TiO₂ plasmonic photoanode modified dye-sensitized solar cells showed enhanced photovoltaic performance due to surface plasmon resonance effect.

Promotional effect of silver nanoparticles on the performance of N-doped TiO2 photoanode-based dye-sensitized solar cells

We report the first successful application of an N-TiO₂–Ag nanocomposite as an efficient photoanode for highly efficient dye-sensitized solar cells (DSSC).