Dye-sensitized solar cells based on trench structured TiO2 nanotubes in Ti substrate

We have proposed dye-sensitized solar cells (DSSCs) with trench-type TiO₂ nanotube structure to improve the low device efficiency of conventional TiO₂ nanotube DSSCs using Ti substrate. Compared to the conventional standing-type TiO₂ nanotube structure based DSSCs, the trench-type TiO₂ nanotube structure based DSSCs have shown an improvement of device efficiency of approximately 40% due to the large increase of Jsc. In the trench-type TiO₂ nanotube structure, the contact area between the TiO₂ nanotube sidewall and the Ti substrate is significantly increased. This increase of contact area provides more charge transport paths than exist in the conventional standing-type TiO₂ nanotube structure and reduces the electrical resistance between the Ti substrate and the TiO₂ nanotubes. Therefore, the remarkable increase of Jsc is the result of the charge collection efficiency, which is improved due to the increase of contact area between the TiO₂ nanotube sidewall and the Ti substrate in the trench-type TiO₂ nanotube structure. The fabrication of the trench-type TiO₂ nanotube structure is an effective manufacturing process for improving the device efficiency of TiO₂ nanotube based DSSCs using Ti substrate. DSSCs having an 11.9 μm thick trench-type TiO₂ nanotube structure have shown an efficiency of 5.74%.     

Thickness effect of the TiO2 nanofiber scattering layer on the performance of the TiO2 nanoparticle/TiO2 nanofiber-structured dye-sensitized solar cells

TiO₂ nanofibers (NFs) were fabricated by an electrospinning process and were used as scattering layers in dye-sensitized solar cells (DSSCs). The NF-coated photoanodes of the DSSCs were prepared with a variety of scattering layer thicknesses. The thickness effect of the scattering layer on the double-layered TiO₂ nanoparticle (NP)/TiO₂ NF structure was investigated through structural, morphological, and optical measurements. In the double-layered photoanode, the TiO₂ NP layer plays a major role in dye adsorption and light transmission, and the TiO₂ NF scattering layer improves the absorption of visible light due to the light scattering effects. The scattering effect of TiO₂ NFs layer was examined by the incident monochromatic photon-to-electron conversion efficiency (IPCE) and UV–Vis spectrometry. The conversion efficiency for the 12 μm-thick photoanode composed of a 2 μm-thick TiO₂ NF layer and 10 μm-thick TiO₂ NP layer was higher than that of DSSCs with only TiO₂ NPs photoanode by approximately 33%.     

One-step hydrothermal synthesis of feather duster-like NiS@MoS<Subscript>2</Subscript> with hierarchical array structure for the Pt-free dye-sensitized solar cell

Novel feather duster-like nickel sulfide (NiS) @ molybdenum sulfide (MoS₂) with hierarchical array structure is synthesized via a simple one-step hydrothermal method, in which a major structure of rod-like NiS in the center and a secondary structure of MoS₂ nanosheets with a thickness of about 15–55 nm on the surface. The feather duster-like NiS@MoS₂ is employed as the counter electrode (CE) material for the dye-sensitized solar cell (DSSC), which exhibits superior electrocatalytic activity due to its feather duster-like hierarchical array structure can not only support the fast electron transfer and electrolyte diffusion channels, but also can provide high specific surface area (238.19 m² g^?1) with abundant active catalytic sites and large electron injection efficiency from CE to electrolyte. The DSSC based on the NiS@MoS₂ CE achieves a competitive photoelectric conversion efficiency of 8.58%, which is higher than that of the NiS (7.13%), MoS₂ (7.33%), and Pt (8.16%) CEs under the same conditions.

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Graphical abstract Novel feather duster-like NiS@MoS₂ hierarchical structure array with superior electrocatalytic activity was fabricated by a simple one-step hydrothermal method.

     

Influence of MoS2 deposition time on the photocatalytic activity of MoS2/ V,N co-doped TiO2 heterostructure thin film in the visible light region

Electron-hole separation and a narrow band-gap are essential steps to obtain efficient photocatalysis, towards which the use of co-catalysts or co-doped-TiO₂ photocatalysts has become a widely used strategy. In this article, the combination of MoS₂ and co-doping of V, N is the goal to achieve high performance photocatalysts. We synthesized MoS₂/V, N co-doped TiO₂ heterostructure thin film by sol-gel and chemical bath deposition methods. Herein, we investigated the influence of deposition time of MoS₂ layer on visible-photocatalytic activity of the obtained samples. The thin films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and UV–vis spectroscopy techniques. Visible-photocatalytic activity of these samples were evaluated on the removal of methylene blue (MB) under visible light irradiation. The results show that the aforementioned heterostructure thin films have better photocatalytic activities than those of TiO₂, MoS₂ and V, N co-doped TiO₂ counterparts in visible light region. The mechanism for increasing visible-photocatalytic property of the heterostructure thin films is discussed in detail. We find that MoS₂/V, N co-doped TiO₂ heterostructure thin film at MoS₂ deposition time of 45-min shows the highest photocatalytic performance in the visible light region with MB photodegradation rate about 99% for 150 min and the degradation rate constant is 2.06 times higher than that of V and N co-doped TiO₂ counterpart.     

Dye-sensitized solar cells based on ZnO nanowire array/TiO2 nanoparticle composite photoelectrodes with controllable nanowire aspect ratio

The ZnO nanowire (NW) array/TiO₂ nanoparticle (NP) composite photoelectrode with controllable NW aspect ratio has been grown from aqueous solutions for the fabrication of dye-sensitized solar cells (DSSCs), which combines the advantages of the rapid electron transport in ZnO NW array and the high surface area of TiO₂ NPs. The results indicate that the composite photoelectrode achieves higher overall photoelectrical conversion efficiency (η) than the ZnO NW alone. As a result, DSSCs based on the ZnO NW array/TiO₂ NP composite photoelectrodes get the enhanced photoelectrical conversion efficiency, and the highest η is also achieved by rational tuning the aspect ratio of ZnO NWs. With the proper aspect ratio (ca. 6) of ZnO NW, the ZnO NW array/TiO₂ NP composite DSSC exhibits the highest conversion efficiency (5.5 %). It is elucidated by the dye adsorption amount and interfacial electron transport of DSSCs with the ZnO NW array/TiO₂ NP composite photoelectrode, which is quantitatively characterized using the UV-Vis absorption spectra and electrochemical impedance spectra. It is evident that the DSSC with the proper aspect ratio of ZnO NW displays the high dye adsorption amount and fastest interfacial electron transfer.     

Controlled Formation of TiO2/MoS2 Core–Shell Heterostructures with Enhanced Visible‐Light Photocatalytic Activities

Most recently, much attention has been devoted to photocatalytic materials that may help to solve the global energy crisis and may provide environmental protection. Herein, novel cocatalysts based on few layered MoS₂ and TiO₂ nanomaterials have been designed by growing MoS₂ nanosheets on the surface of TiO₂ nanospheres through a facile hydrothermal method. The method allows the formation of TiO₂/MoS₂ core–shell heterostructures of uniform morphologies and stable structure and provides a good control over shell thickness. The mechanism that forms these heterostructures is discussed in detail. In addition, as cocatalyst, MoS₂ nanosheets can enlarge the light harvesting window to include visible light and improve the photocatalytic ability of TiO₂. Using Rhodamine B as the model, the resultant heterostructure is demonstrated to possess excellent and stable photocatalytic activity in the degradation of organic pollutants under visible light illumination. The TiO₂/MoS₂ heterostructures possess this catalytic activity due to their large surface area and their excellent interface for separating holes and electrons. Therefore, this novel heterostructure nanomaterials possess potential applications in water treatment, degradation of dye pollutants, and environmental cleaning.     

Effects of ZnO coating on the performance of TiO2 nanostructured thin films for dye-sensitized solar cells

ZnO-coated TiO₂ (ZTO) thin films were deposited on ITO substrates by a sol–gel method for application as the work electrode for dye-sensitized solar cells (DSSCs). The I–V curve and the incident photon-to-current conversion efficiency (IPCE) value of DSSCs for ZTO thin films were studied and compared with single TiO₂ films. The results show that the short-circuit photocurrent (J _sc) and open-circuit voltage (V _oc) values increased from 3.7 mA/cm² and 0.68 V for the DSSCs with a single TiO₂ film to 4.5 mA/cm² and 0.72 V, respectively, for the DSSCs with a ZTO thin film. It indicated that the DSSCs with a ZTO thin film contributed to provide an inherent energy barrier that suppressed charge recombination significantly. In addition, the higher IPCE value in the ZTO thin film is attributed to the better charge separation by a fast electron transfer process using two semiconductors with different conduction band edges and energy positions.     

Dependence of photovoltaic parameters on the size of cations adsorbed by TiO2 photoanode in dye-sensitized solar cells

The effects of “pre-adsorbed cations” in photoanodes on the performances of dye-sensitized solar cells (DSSCs) were studied using two different size cations (K⁺ and guanidine cation (G⁺)). While the DSSCs with optimized K⁺ ions pre-adsorbed photoanodes showed a maximum efficiency of 7.04%, the DSSCs with G⁺ ions pre-adsorbed photoanodes showed an efficiency of 6.73%. DSSCs fabricated with conventional photanodes (without pre-cation adsorption) showed an efficiency of 6.21%. Differences in efficiencies are very likely due to the cation pre-adsorption effects and could be due to a higher number of K⁺ cation adsorption per unit area of TiO₂ surface of the photoanode compared to a smaller number of G⁺ cation adsorption in TiO₂, due to their difference in sizes. This pre-cation adsorption technique can be used to improve the overall efficiency of a DSSC by about 14% fold over the conventional photoanodes use in DSSCs, specially using smaller cations.

     

ZnO/TiO2 core–shell nanowire arrays for enhanced dye-sensitized solar cell efficiency

We present a new method of synthesizing ZnO/TiO₂ core–shell nanowire (NW) arrays for the fabrication of dye-sensitized solar cells (DSSCs). Vertically aligned ZnO NW arrays were obtained on Si substrates, and modified by a TiO₂ shell in order to solve the recombination problems via a cost-effective spin-coating method. The structure of the ZnO/TiO₂ composite NW arrays was characterized. The experimental results indicate that the TiO₂ shell enhances the performance of the DSSCs, through improving the stability of the ZnO NWs and decreasing the recombination of photogenerated electrons on the NW surface. The highest overall conversion efficiency of the cell reaches about 3.0 %.     

Chemical reactions in TiO2/SnO2/TiCl4 hybrid electrodes and their impacts to power conversion efficiency of dye-sensitized solar cells

This study examined the applicability of TiO₂/SnO₂/TiCl₄ hybrid electrodes in dye-sensitized solar cells (DSSCs) by combining chemical modeling with experimentation. The interfacial chemical reactions in a TiO₂/SnO₂/TiCl₄ system were simulated using a thermochemistry software package, which led to the design and testing of hybrid working electrodes. Chemical thermodynamic modeling proved that TiCl₄ is an effective agent in removing Tiⁿ⁺ (n<4) and Sn^m+ (m<4) ion impurities from dry-mixed TiO₂/SnO₂ composite particles. Our results demonstrate that the power conversion efficiency of DSSC with a TiO₂/SnO₂/TiCl₄ hybrid electrode exceeds that of the conventional DSSC with a TiO₂ electrode due to the effects of light-scattering and the formation of additional absorbance (SnCl₂), which is an unexpected side effect of TiCl₄ treatment enabling the absorption of visible light. The proposed approach is ideally suited to establishing relationships between chemistry theory and the structure and performance of advanced DSSCs as well as photo-electro-chemical systems.     

Enhanced lithium-ion storage and hydrogen evolution reaction catalysis of MoS<Subscript>2</Subscript>/graphene nanoribbons hybrids with loose interlaced three-dimension structure

Molybdenum disulfide hybridized with graphene nanoribbon (MoS₂/GNR) was prepared by mild method. MoS₂/GNR hybrids interlace loosely into a three-dimension structure. GNR hybridization can improve the dispersity of MoS₂, reduce the grain size of MoS₂ to 3–6 nm, increase the specific surface area, and broaden the interlamellar spacing of MoS₂ (002) plane to 0.67–0.73 nm, which facilitates the transportation of Li⁺ ions for lithium-ion battery. MoS₂/GNR hybrids have better cyclic durability, higher specific discharge capacity, and superior rate performance than MoS₂. The electrocatalytic activity in hydrogen evolution reaction shows that MoS₂/GNR hybrids have the lower overpotential and the larger current density with a negligible current loss after 2000 cycles. Hybridizing with GNRs enhances both the lithium-ion electrochemical storage and the electrocatalytic activity of MoS₂.

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Graphical abstract MoS₂/GNR hybrid prepared by a mild method is interlaced loosely into a three-dimension structure. Superior electrochemical performances of MoS₂/GNR hybrids than MoS₂ have been highlighted for the potential application for long- term durability energy-storage devices and HER electrocatalytic materials.

     

Nanoparticulate TiO2-promoted PtRu/C catalyst for methanol oxidation

To improve the electrocatalytic properties of PtRu/C in methanol electrooxidation, nanoparticulate TiO₂-promoted PtRu/C catalysts were prepared by directly mixing TiO₂ nanoparticles with PtRu/C. Using cyclic voltammetry, it was found that the addition of 10 wt% TiO₂ nanoparticles can effectively improve the electrocatalytic activity and stability of the catalyst during methanol electrooxidation. The value of the apparent activation energy (E _a) for TiO₂-PtRu/C was lower than that for pure PtRu/C at a potential range from 0.45 to 0.60 V. A synergistic effect between PtRu and TiO₂ nanoparticles is likely to facilitate the removal of CO-like intermediates from the surface of PtRu catalyst and reduce the poisoning of the PtRu catalysts during methanol electrooxidation. Therefore, we conclude that the direct introduction of TiO₂ nanoparticles into PtRu/C catalysts offers an improved facile method to enhance the electrocatalytic performance of PtRu/C catalyst in methanol electrooxidation.     

Anodic TiO<Subscript>2</Subscript> nanotubes powder and its application in dye-sensitized solar cells

An increasing energy demand and environmental pollution create a pressing need for clean and sustainable energy solutions. TiO₂ semiconductor material is expected to play an important role in helping solve the energy crisis through effective utilization of solar energy based on photovoltaic devices. Dye-sensitized solar cells (DSSCs) are potentially lower cost alternative to inorganic silicon-based photovoltaic cells. In this study, we report on the fabrication of DSSCs from anodic TiO₂ nanotubes (NT) powder, produced by rapid breakdown potentiostatic anodization of Ti foil in 0.1 M HClO₄ electrolyte, as photoanode. TiO₂ NT powders with a typical NT outer diameter of approximately 40 nm, wall thickness of approximately 8–15 nm, and length of about 20–25 μm, have been synthesized. The counter electrode was made by electrodeposition of Pt from an aqueous solution of 5 mM H₂PtCl₆ onto fluorine-doped tin oxide (FTO) glass substrate. The above front-side illuminated DSSCs were compared with back-side illuminated DSSCs fabricated from anodic TiO₂ NTs that were grown on the top of Ti foil as photoanode. The highest cell efficiency was 3.54% under 100 mW/cm² light intensity (1 sun AM 1.5G light, Jsc = 14.3 mA/cm², Voc = 0.544 V, FF = 0.455). To the best of our knowledge, this is the first report on the fabrication of DSSC from anodic TiO₂ NTs powder. The TiO₂/FTO photoanodes were characterized by FE-SEM, XRD, and UV–Visible spectroscopy. The catalytic properties of Pt/FTO counter electrodes have been examined by cyclic voltammetry.     

Influence of TiO2 nanotube morphology and TiCl4 treatment on the charge transfer in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated using TiO₂ nanoparticles (NPs), TiO₂ nanotube arrays (NTAs), and surface-modified NTAs with a TiCl₄ treatment. The photovoltaic efficiencies of the DSSCs using TiO₂ NP, NTA, and TiCl₄-treated NTA electrodes are 4.25, 4.74, and 7.47 %, respectively. The highest performance was observed with a TiCl₄-treated TiO₂ NTA photoanode, although in the case of the latter two electrodes, the amounts of N719 dye adsorbed were similar and 68 % of that of the NP electrode. Electrochemical impedance measurements show that the overall resistance, including the charge–transfer resistance, was smaller with NTA morphologies than with NP morphologies. We suggest that a different electron transfer mechanism along the one-dimensional nanostructure of the TiO₂ NTAs contributes to the smaller charge–transfer resistance, resulting in a higher short circuit current (J _sc), even at lower dye adsorption. Furthermore, the TiCl₄-treated NTAs showed even smaller charge–transfer resistance, resulting in the highest J _sc value, because the downward shift in the conduction band edge improves the electron injection efficiency from the excited dye into the TiCl₄-treated TiO₂ electrodes.     

A facile low temperature synthesis of TiO2 nanorods for high efficiency dye sensitized solar cells

Titania (TiO₂) nanorods have been synthesized with controlled size for dye-sensitized solar cells (DSSCs) via hydrothermal route at low hydrothermal temperature of 100 °C for 24 h. The titania nanorods were characterized using XRD, SEM, TEM/HRTEM, UV-vis Spectroscopy, FTIR and BET specific surface area (S _BET), as well as pore-size distribution by BJH. The results indicated that the bulk traps and the surface states within the TiO₂ nanorods films have enhanced the efficiency of DSSCs. The size of the titania nanorods was 6.7 nm in width and 22 nm in length. The high surface area can provide more sites for dye adsorption, while the fast photoelectron-transfer channel can enhance the photogenerated electron transfer to complete the circuit. The specific surface area S _BET was 77.14 m²?g^?1 at the synthesis conditions. However, the band gap energy of the obtained titania nanorods was 3.2 eV. The oriented nanorods with appropriate lengths are beneficial in improving the electron transport property and thus leading to the increase of photocurrent, together enhancing the power conversion efficiency. A nearly quantitative absorbed photon-to-electrical current conversion achieved upon excitation at wave length of 550 nm and the power efficiency was enhanced from 5.6 % for commercial TiO₂ nanoparticles Degussa (P25) cells to 7.2 % for TiO₂ nanorods cells under AM 1.5 illumination (100 mW?cm^?2). The TiO₂ cells performance was improved due to their high surface area, hierarchically mesoporous structures and fast electron-transfer rate compared with the Degussa (P25).     

40% Efficiency enhancement in solar cells using ZnO nanorods as shell prepared via novel hydrothermal synthesis

Herein, rod-like ZnO nanostructures were synthesized via a novel hydrothermal route using Zn(OAc)₂, ethylenediamine and hydrazine as a new set of starting reagents. The as-synthesized products were characterized by techniques including XRD, EDS, SEM, XPS, Pl and FTIR. The prepared ZnO nanostructures were utilized as shell on TiO₂ film in DSSCs. Effect of precursor type, morphology and thickness of ZnO shell (number of electrophoresis cycle) on solar cells efficiency were well studied. Our results showed that ethylenediamine has crucial effect on morphology of synthesized ZnO nanostructures and using ZnO nanostructures leads to an increase in DSSCs efficiency compared to bare TiO₂ from 4.66 to 7.13% (~40% improvement). Moreover, highest amount of solar cell efficiency (7.13%) was obtained by using ZnO nanorods with two cycle of electrophoresis for deposition.     

Three-dimensional flower-like NiS2/MoS2 assembly of randomly oriented nanoplate for enhanced hydrogen evolution reaction

The continually worsening energy crisis has stimulated research into energy conversion technology to produce pure hydrogen, H₂. Transition metal-based compounds have attracted great attention as electrocatalysts for hydrogen evolution reaction (HER) as alternatives to commercial, high-cost, and scarce noble metal-based catalysts. In this work, a 3D flower-like NiS₂/MoS₂ is synthesized with the advantages of a three-dimensional (3D) morphology and the compositing of different metal compounds, thus leading to enhanced electrocatalytic performance. The structure of 3D flower-like NiS₂/MoS₂ augments the specific surface areas resulting from nanoplate assemblies as well as the heterointerface ascribed to two different phases of NiS₂ and MoS₂. These characteristics are confirmed by electrocatalytic measurements of the lower overpotential of 165 mV at 10 mA/cm² with high charge transfer ability, thus demonstrating the structure's potential for advanced electrocatalysts for the HER.     

A facile sonochemical route for the synthesis of MoS2/Pd composites for highly efficient oxygen reduction reaction

For the alkaline fuel cell cathode reaction, it is very essential to develop novel catalysts with superior catalytic properties. Here, we report the synthesis of highly active and stable MoS₂/Pd composites for the oxygen reduction reaction (ORR), via a simple, eco-friendly sonochemical method. The bulk MoS₂ was first transformed into single and few layers MoS₂ nanosheets through ultrasonic exfoliation. Then the exfoliated MoS₂ nanosheets served as supporting materials for the nucleation and further in-situ growth of Pd nanoparticles to form MoS₂/Pd composites via ultrasonic irradiation. Cyclic voltammetry and rotating disk voltammetry measurements demonstrate that as-prepared MoS₂/Pd composites which provides a direct four-electron pathway for the ORR, have better electrocatalytic activity, long-term operation stability than commercial Pt/C catalyst. We expect that the present work would provide a promising strategy for the development of efficient oxygen reduction electrocatalyst. In addition, this study can also be extended to the preparation of other hybrid with desirable morphologies and functions.     

关联染料敏化太阳能电池薄膜厚度与光伏性能的漂移-扩散数值模拟

建立漂移-扩散模型来模拟敏化电池的电荷分离过程.该模型能够计算在稳态和非稳态条件下光生电子的多步受限扩散及其与电子受体的复合反应.通过对电池的电流-电压曲线的数值模拟,优化了电池的薄膜厚度并获得了最大的光电转换效率.发现膜厚的增加降低了电荷收集效率,但有利于提高电子注入流率,光电流的输出正是受控于这两个因素.复合速率常数严重影响了膜厚优化的结果.较厚的薄膜适合于电子复合被充分抑制的电池,而较薄的薄膜有利于降低快复合电池的电子复合损失.在开路条件下,膜厚的提高会减小电子浓度,在造成光电压的降低的同时会提高电子寿命.     

One-pot,large-scale synthesis silica-encapsulated NIR alloy quantum dots CdSeTe within short time

Hydrothermal process has been employed to synthesize titanium oxide (TiO₂) bottle brush. The nanostructured bottle brushes with tetragonal nanorods of ~75 nm diameter have been synthesized by changing the nature of the precursors and hydrothermal processing parameters. The morphological features and structural properties of TiO₂ films were investigated by field emission scanning electron microscopy, X-ray diffraction, high-resolution transmission electron spectroscopy, Fourier transform Raman spectroscopy, and X-ray photoelectron spectroscopy. The influence of such nanostructures on the performance of dye-sensitized solar cells (DSSCs) is investigated in detail. The interface and transient properties of these nanorods and bottle brush-based photoanodes in DSSCs were analyzed by electrochemical impedance spectroscopic measurements in order to understand the critical factors contributing to such high power conversion efficiency. Surface area of sample was recorded using Brunauer–Emmett–Teller measurements. It is found that bottle brush provides effective large surface area 89.34 m² g^?1 which is much higher than TiO₂ nanorods 63.7 m² g^?1. Such effective surface area can facilitate the effective light harvesting, and hence improves the dye adsorption and the photovoltaic performance of DSSCs, typically in short-circuit photocurrent and power conversion efficiency. A best power conversion efficiency of 6.63 % has been achieved. We believe that the present device performance would have wide interests in dye-sensitized solar cell research.