One‐Pot Synthesis of Dual Stimulus‐Responsive Degradable Hollow Hybrid Nanoparticles for Image‐Guided Trimodal Therapy

Exploiting exogenous and endogenous stimulus‐responsive degradable nanoparticles as drug carriers can improve drug delivery systems (DDSs). The use of hollow nanoparticles may facilitate degradation, and combination of DDS with photodynamic therapy (PDT) and photothermal therapy (PTT) may enhance the anticancer effects of treatments. Here, a one‐pot synthetic method is presented for an anticancer drug (doxorubicin [DOX]) and photosensitizer‐containing hollow hybrid nanoparticles (HNPs) with a disulfide and siloxane framework formed in response to exogenous (light) and endogenous (intracellular glutathione [GSH]) stimuli. The hollow HNPs emit fluorescence within the near‐infrared window and allow for the detection of tumors in vivo by fluorescence imaging. Furthermore, the disulfides within the HNP framework are cleaved by intracellular GSH, deforming the HNPs. Light irradiation facilitates penetration of GSH into the HNP framework and leads to the collapse of the HNPs. As a result, DOX is released from the hollow HNPs. Additionally, the hollow HNPs generate singlet oxygen (¹O₂) and heat in response to light; thus, fluorescence imaging of tumors combined with trimodal therapy consisting of DDS, PDT, and PTT is feasible, resulting in superior therapeutic efficacy. Thus, this method may have several applications in imaging and therapeutics in the future.     

Conformal Nano‐Sized Inorganic Coatings on Mesoporous TiO2 Films for Low‐Temperature Dye‐Sensitized Solar Cell Fabrication

Here, a new method based on sol–gel electrophoretic deposition to produce uniform high‐quality inorganic conformal coatings on mesoporous nano‐particulate films is presented. This novel sol preparation method allows for very fine control of the coating properties, thus inducing new adjustable functionalities to these electrodes. It is shown that the deposition of an amorphous TiO₂ and/or MgO shell onto photoanodes used in dye‐sensitized solar cells (DSSCs) improves their light‐to‐electric‐power conversion efficiency without the need for sintering. It is proposed that the amorphous TiO₂ coating improves the electronic inter‐particle connection and passivates the surface states. The insulating MgO coating further reduces the electron transfer from the conduction band into the electrolyte while the electron injection from the excited dye state remains unperturbed for thin coatings. Using a low‐temperature method for DSSC production on plastic substrates, a maximum efficiency of 6.2% applying pressure together with an optimized TiO₂ coating is achieved. For systems that cannot be pressed a conversion efficiency of 5.1% is achieved using a double shell TiO₂/MgO coating.     

Low‐temperature flexible Ti/TiO2 photoanode for dye‐sensitized solar cells with binder‐free TiO2 paste

An energy‐economical dye‐sensitized solar cell (DSSC) with highly flexible Ti/TiO₂ photoanode was developed through a low‐temperature process, using a binder‐free TiO₂ paste. Ti foils, coated with the binder‐free TiO₂ films were annealed at various temperature. Scanning electron microscopic (SEM) images of the films show uniform, mesoporous and crack‐free surface morphologies as well as interpenetrated TiO₂ network. DSSCs with binder‐free TiO₂ films annealed at 450, 350, 250 and 120°C show solar‐to‐electricity conversion efficiencies (η) of 4.33, 4.34, 3.72 and 3.40%, respectively, which are comparable to the efficiency of 4.56% obtained by using a paste with binder and annealing it at 450°C; this observation demonstrates the benefits of a binder‐free TiO₂ paste for the fabrication of energy‐fugal DSSCs. On the other hand, when organic binder was used in the TiO₂ paste for film preparation, a drastic deterioration in the cell performance with decreasing annealing temperature is noticed. Laser‐induced photo‐voltage transient technique is used to estimate the electron lifetime in various Ti/TiO₂ films. Electrochemical impedance spectroscopic (EIS) analysis shows that the lower the annealing temperature of the TiO₂ coated Ti foil, the larger the charge transfer resistance at the TiO₂/dye/electrolyte interface (R_ct2). Copyright © 2011 John Wiley & Sons, Ltd.     

Large‐scale Synthesis of Urchin‐like Mesoporous TiO2 Hollow Spheres by Targeted Etching and Their Photoelectrochemical Properties

A versatile targeted etching strategy is developed for the large‐scale synthesis of urchin‐like mesoporous TiO₂ hollow spheres (UMTHS) with tunable particle size. Its key feature is the use of a low‐temperature hydrothermal reaction of surface‐fluorinated, amorphous, hydrous TiO₂ solid spheres (AHTSS) under the protection of a polyvinylpyrrolidone (PVP) coating. With the confinement of PVP and water penetration, the highly porous AHTSS are selectively etched and hollowed by fluoride without destroying their spherical morphology. Meanwhile TiO₂ hydrates are gradually crystallized and their growth is preferentially along anatase (101) planes, reconstructing an urchin‐like shell consisting of numerous radially arranged single‐crystal anatase nanothorns. Complex hollow structures, such as core–shell and yolk–shell structures, can also be easily synthesized via additional protection of the interior by pre‐filling AHTSS with polyethylene glycol (PEG). The hollowing transformation is elucidated by the synergetic effect of etching, PVP coating, low hydrothermal reaction temperature, and the unique microstructure of AHTSS. The synthesized UMTHS with a large surface area of up to 128.6 m² g^‐1 show excellent light‐harvesting properties and present superior performances in photocatalytic removal of gaseous nitric oxide (NO) and photoelectrochemical solar energy conversion as photoanodes for dye‐sensitized mesoscopic solar cells.     

Enhancing the Performance of Solid‐State Dye‐Sensitized Solar Cells Using a Mesoporous Interfacial Titania Layer with a Bragg Stack

High efficiency dye‐sensitized solar cells (DSSCs) are fabricated with a heterostructured photoanode that consists of a 500‐nm‐thick organized mesoporous TiO₂ (om‐TiO₂) interfacial layer (IF layer), a 7 or 10‐μm thick nanocrystalline TiO₂ layer (NC layer), and a 2‐μm‐thick mesoporous Bragg stack (meso‐BS layer) as the bottom, middle and top layers, respectively. An om‐TiO₂ layer with a high porosity, transmittance, and interconnectivity is prepared via a sol‐gel process, in which a poly(vinyl chloride)‐g‐poly(oxyethylene methacrylate) (PVC‐g‐POEM) graft copolymer is used as a structure‐directing agent. The meso‐BS layer with large pores is prepared via alternating deposition of om‐TiO₂ and colloidal SiO₂ (col‐SiO₂) layers. Structure and optical properties (refractive index) of the om‐TiO₂ and meso‐BS layers are studied and the morphology of the heterostructured photoanode is characterized. DSSCs fabricated with the heterostructured IF/NC/BS photoanode and combined with a polymerized ionic liquid (PIL) exhibit an energy conversion efficiencies of 6.6% at 100 mW/cm², one of the highest reported for solid‐state DSSCs and much larger than cells prepared with only a IF/NC layer (6.0%) or a NC layer (4.5%). Improvements in energy conversion efficiency are attributed to the combination of improved light harvesting, decreased resistance at the electrode/electrolyte interface, and excellent electrolyte infiltration.     

Increasing the Efficiency of Organic Dye‐Sensitized Solar Cells over 10.3% Using Locally Ordered Inverse Opal Nanostructures in the Photoelectrode

3D inverse opal (3D‐IO) oxides are very appealing nanostructures to be integrated into the photoelectrodes of dye‐sensitized solar cells (DSSCs). Due to their periodic interconnected pore network with a high pore volume fraction, they facilitate electrolyte infiltration and enhance light scattering. Nonetheless, preparing 3D‐IO structures directly on nonflat DSSC electrodes is challenging. Herein, 3D‐IO TiO₂ structures are prepared by templating with self‐assembled polymethyl methacrylate spheres on glass substrates, impregnation with a mixed TiO₂:SiO₂ precursor and calcination. The specific surface increases from 20.9 to 30.7 m² g^?1 after SiO₂ removal via etching, which leads to the formation of mesopores. The obtained nanostructures are scraped from the substrate, processed as a paste, and deposited on photoelectrodes containing a mesoporous TiO₂ layer. This procedure maintains locally the 3D‐IO order. When sensitized with the novel benzothiadiazole dye YKP‐88, DSSCs containing the modified photoelectrodes exhibit an efficiency of 10.35% versus 9.26% for the same devices with conventional photoelectrodes. Similarly, using the ruthenium dye N719 as sensitizer an efficiency increase from 5.31% to 6.23% is obtained. These improvements originate mainly from an increase in the photocurrent density, which is attributed to an enhanced dye loading obtained with the mesoporous 3D‐IO structures due to SiO₂ removal.     

TiO2 Microspheres with Controllable Surface Area and Porosity for Enhanced Light Harvesting and Electrolyte Diffusion in Dye‐Sensitized Solar Cells

An optimized configuration of TiO₂ microspheres in photoanodes is of great importance to prepare highly efficient dye‐sensitized solar cells (DSSCs). In this work, TiO₂ microspheres with tunable diameter, pore size, and porosity are synthesized by subtly adjusting the synthesizing conditions, including ratios of deionized water, ammonia, and ethanol, respectively. TiO₂ microspheres are obtained with large pore sizes and a high porosity without sacrificing specific surface areas. In addition, the effect of their porosity and pore size on the performance of DSSCs is investigated. As confirmed by the dye‐loading ability and electrolyte diffusion resistance, the large mesopores and the high porosity of the TiO₂ microspheres can improve dye adsorption and facilitate electrolyte diffusion, giving rise to a high light‐harvesting and electron collection efficiency. Consequently, the highest photocurrent of 19.21 mA cm^?2 and a power conversion efficiency of 9.98% are obtained by using the TiO₂ microspheres with the highest porosity, compared with a 9.29% efficiency demonstrated by the lowest porosity (an improvement of 7.4%). By modifying the interconnection and the external pores of the microspheres photoanode, a high efficiency of 11.67% is achieved for a DSSC based on the most potent TiO₂ microspheres.     

Highly Interconnected Porous Electrodes for Dye‐Sensitized Solar Cells Using Viruses as a Sacrificial Template

A novel means of generating highly interconnected and nano‐channeled photoelectrodes by employing one‐dimensionally shaped M13 viruses as a sacrificial template is proposed for highly efficient dye‐sensitized solar cells (DSSCs). The electrostatic binding between oppositely charged TiO₂ nanoparticles and M13 viruses provides a uniform complexation and suppresses random aggregation of TiO₂ nanoparticles. After the calcination process, the traces of viruses leave porously interconnected channel structures inside TiO₂ nanoparticles, providing efficient paths for electrolyte contact as well as increased surface sites for dye adsorption. As a result, DSSCs generated using a sacrificial virus template exhibit an enhanced current density (J_SC) of 12.35 mA cm‐² and a high photoconversion efficiency (η) of 6.32%, greater than those of conventional photoelectrodes made of TiO₂ nanoparticles (J_SC of 8.91 mA cm‐² and η of 4.67%). In addition, the stiffness and shape of the M13 virus can be varied, emphasizing the usefulness of the one‐dimensional structural characteristics of M13 viruses for the highly interconnected porous structure of DSSC photoelectrodes.     

Dye‐sensitized TiO2 solar cells based on nanocomposite photoanode containing plasma‐modified multi‐walled carbon nanotubes

A series of anatase TiO₂‐based nanocomposite incorporated with plasma‐modified multi‐walled carbon nanotubes (MWNTs) was prepared by physical blending and shows its capability for efficient electron transport when used as photoanode in dye‐sensitized solar cells (DSSCs). These MWNTs characterized with good dispersal performance were obtained by functionalization technique via in situ plasma treatment and subsequent grafting with maleic anhydride (MA) onto the external walls reported previously. Compared with the conventional DSSCs, the TiO₂ film with 1D carbon nanotubes possesses more outstanding ability to transport electrons injected from the excited dye within the device under illumination. As a result, at an optimum addition of 0.3 wt% MWNTs‐MA in TiO₂ matrix, the photocurrent–voltage (J–V) characteristics showed a significant increase in the short‐circuit photocurrent (J_sc) of 50%, leading to an increase in overall solar conversion efficiency by a factor of 1.5. Electrochemical impedance spectroscopy analyses reveal that the MWNTs‐MA/TiO₂ incur smaller resistances at the photoanode in assembled DSSCs when compared with those in the anatase titania DSSCs. These features suggest that the conducting properties of the MWNTs‐MA within the anodes are crucial for achieving a higher transport rate for photo‐induced electrons in TiO₂ layer by exhibiting lower resistance in the porous network and hence retard charge recombination that could result in poor conversion efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

Mesoporous Anatase Titania Hollow Nanostructures though Silica‐Protected Calcination

The crystallization of nanometer‐scale materials during high‐temperature calcination can be controlled by a thin layer of surface coating. Here, a novel silica‐protected calcination process for preparing mesoporous hollow TiO₂ nanostructures with a high surface area and a controllable crystallinity is presented. This method involves the preparation of uniform silica colloidal templates, sequential deposition of TiO₂ and then SiO₂ layers through sol–gel processes, calcination to transform amorphous TiO₂ to crystalline anatase, and finally etching of the inner and outer silica to produce mesoporous anatase TiO₂ shells. The silica‐protected calcination step allows crystallization of the amorphous TiO₂ layer into anatase nanocrystals, while simultaneously limiting the growth of anatase grains to within several nanometers, eventually producing mesoporous anatase shells with a high surface area (～311 m² g^?1) and good water dispersibility upon chemical etching of the silica. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the as‐synthesized mesoporous anatase shells show significantly enhanced photocatalytic activity with greater enhancement for samples calcined at higher temperatures thanks to their improved crystallinity.     

Room‐Temperature Synthesis of Porous Nanoparticulate TiO2 Films for Flexible Dye‐Sensitized Solar Cells

A novel room‐temperature method for the preparation of porous TiO₂ films with high performance in dye‐sensitized solar cells (DSSCs) has been developed. In this method a small amount of Ti^IV tetraisopropoxide (TTIP) is added to an ethanolic paste of TiO₂ nanoparticles, where it hydrolyzes in situ and connects the TiO₂ particles to form a homogenous and mechanically stable film of up to 10 μm thickness without crack formation. Residual organics originating from the TTIP were removed by UV–ozone treatment of the films, leading to a remarkable improvement of the cell efficiency. Intensity‐modulated photocurrent/voltage spectroscopy (IMPS/IMVS) showed that the main effect of the UV–ozone treatment is to suppress the recombination of photogenerated electrons, thereby extending their lifetime. The efficiency was further increased by preheating the TiO₂ nanoparticles before the paste preparation to remove contaminants originating from the preparation process of the particles. Solar‐to‐electric energy conversion efficiencies of 4.00 and 3.27 % have been achieved for cells with conductive glass and plastic film substrates, respectively, under illumination with AM 1.5 (100 mW cm^–2) simulated sunlight.     

Photosystem I‐based Biophotovoltaics on Nanostructured Hematite

The electronic coupling between a robust red algal photosystem I (PSI) associated with its light harvesting antenna (LHCI) and nanocrystalline n‐type semiconductors, TiO₂ and hematite (α‐Fe₂O₃) is utilized for fabrication of the biohybrid dye‐sensitized solar cells (DSSC). PSI‐LHCI is immobilized as a structured multilayer over both semiconductors organized as highly ordered nanocrystalline arrays, as evidenced by FE‐SEM and XRD spectroscopy. Of all the biohybrid DSSCs examined, α‐Fe₂O₃/PSI‐LHCI biophotoanode operates at a highest quantum efficiency and generates the largest open circuit photo­current compared to the tandem system based on TiO₂/PSI‐LHCI material. This is accomplished by immobilization of the PSI‐LHCI complex with its reducing side towards the hematite surface and nanostructuring of the PSI‐LHCI multilayer in which the subsequent layers of this complex are organized in the head‐to‐tail orientation. The biohybrid PSI‐LHCI‐DSSC is capable of sustained photoelectrochemical H₂ production upon illumination with visible light above 590 nm. Although the solar conversion efficiency of the PSI‐LHCI/hematite DSSC is currently below a practical use, the system provides a blueprint for a genuinely green solar cell that can be used for molecular hydrogen production at a rate of 744 μmoles H₂ mg Chl^?1 h^?1, placing it amongst the best performing biohybrid solar‐to‐fuel nanodevices.     

Fabrication and Shell Optimization of Synergistic TiO2‐MoO3 Core–Shell Nanowire Array Anode for High Energy and Power Density Lithium‐Ion Batteries

A novel synergistic TiO₂‐MoO₃ (TO‐MO) core–shell nanowire array anode has been fabricated via a facile hydrothermal method followed by a subsequent controllable electrodeposition process. The nano‐MoO₃ shell provides large specific capacity as well as good electrical conductivity for fast charge transfer, while the highly electrochemically stable TiO₂ nanowire core (negligible volume change during Li insertion/desertion) remedies the cycling instability of MoO₃ shell and its array further provides a 3D scaffold for large amount electrodeposition of MoO₃. In combination of the unique electrochemical attributes of nanostructure arrays, the optimized TO‐MO hybrid anode (mass ratio: ca. 1:1) simultaneously exhibits high gravimetric capacity (ca. 670 mAh g^?1; approaching the hybrid's theoretical value), excellent cyclability (>200 cycles) and good rate capability (up to 2000 mA g^?1). The areal capacity is also as high as 3.986 mAh cm^?2, comparable to that of typical commercial LIBs. Furthermore, the hybrid anode was assembled for the first time with commercial LiCoO₂ cathode into a Li ion full cell, which shows outstanding performance with maximum power density of 1086 W kg_total ^?1 (based on the total mass of the TO‐MO and LiCoO₂) and excellent energy density (285 Wh kg_total ^?1) that is higher than many previously reported metal oxide anode‐based Li full cells.     

The use of Ti meshes with self‐organized TiO2 nanotubes as photoanodes of all‐Ti dye‐sensitized solar cells

This paper reports a simple and facile method for directly growing self‐organized TiO₂ nanotubular arrays around the whole Ti mesh by electrochemical anodization in organic electrolytes and their application in all‐Ti dye‐sensitized solar cells (DSSCs). Compared with the traditional fluorine‐doped tin oxide (FTO)‐based DSSC and the backside illuminated DSSC, this type of DSSC showed advantages such as low resistance, cheap fabrication cost and enhanced sunlight utilization. Different thicknesses of nanotubular array layers were investigated to find their influence on the photovoltaic parameters of the cell. We also considered three types of meshes as the substrates of anodes and found that the cell with 6 openings/mm² exhibited the highest conversion efficiency of 5.3%. The area of the cell had only a little impact on the photovoltaic performances. Copyright © 2010 John Wiley & Sons, Ltd.     

Edge‐Enriched Ultrathin MoS2 Embedded Yolk‐Shell TiO2 with Boosted Charge Transfer for Superior Photocatalytic H2 Evolution

Exploring TiO₂‐photocatalysts for sunlight conversion has high demand in artificial photosynthesis. In this work, edge‐enriched ultrathin molybdenum disulfide (MoS₂) flakes are uniformly embedded into the bulk of yolk‐shell TiO₂ as a cocatalyst to accelerate photogenerated‐electron transfer from the bulk to the surface of TiO₂. The as‐formed MoS₂/TiO₂ (0.14 wt%) hybrids exhibit a high hydrogen evolution rate (HER) of 2443 µmol g^?1 h^?1, about 1000% and 470% of that of pristine TiO₂ (247 µmol g^?1 h^?1) and bulk MoS₂ decorated TiO₂ (513 µmol g^?1 h^?1). Such a greatly enhanced HER is attributed to the exposed catalytic edges of the ultrathin MoS₂ flakes with a robust chemical linkage (Ti? S bond), providing rapid charge transfer channels between TiO₂ and MoS₂. The catalytic stability is promoted by the antiaggregation of the highly dispersed MoS₂ flakes in the bulk of yolk‐shell TiO₂. The exponential fitted decay kinetics of time‐resolved photoluminescence (ns‐PL) spectra illustrates that embedding ultrathin MoS₂ flakes in TiO₂ effectively decreases the average lifetime of PL in the MoS₂/TiO₂ hybrids (τ_ave = 4.55 ns), faster than that of pristine TiO₂ (≈7.17 ns) and the bulk MoS₂/TiO₂ (≈6.13 ns), allowing a superior charge separation and charge trapping process for reducing water.     

Room‐Temperature Micropillar Growth of Lithium–Titanate–Carbon Composite Structures by Self‐Biased Direct Current Magnetron Sputtering for Lithium Ion Microbatteries

Here, an unidentified type of micropillar growth is described at room temperature during conventional direct‐current magnetron sputtering (DC‐MS) deposition from a Li₄Ti₅O₁₂+graphite sputter target under negative substrate bias and high operating pressure. These fabricated carbon–Li₂O–TiO₂ microstructures consisting of various Li₄Ti₅O₁₂/Li₂TiO₃/Li_x TiO₂ crystalline phases are demonstrated as an anode material in Li‐ion microbatteries. The described micropillar fabrication method is a low‐cost, substrate independent, single‐step, room‐temperature vacuum process utilizing a mature industrial complementary metal–oxide–semiconductor (CMOS)‐compatible technology. Furthermore, tentative consideration is given to the effects of selected deposition parameters and the growth process, as based on extensive physical and chemical characterization. Additional studies are, however, required to understand the exact processes and interactions that form the micropillars. If this facile method is further extended to other similar metal oxide–carbon systems, it could offer alternative low‐cost fabrication routes for microporous high‐surface area materials in electrochemistry and microelectronics.     

Sacrificial‐Layer Atomic Layer Deposition for Fabrication of Non‐Close‐Packed Inverse‐Opal Photonic Crystals

A method is presented for predicting and precisely controlling the structure of photonic crystals fabricated using sacrificial‐layer atomic layer deposition. This technique provides a reliable method for fabrication of high‐quality non‐close‐packed inverse shell opals with large static tunability and precise structural control. By using a sacrificial layer during opal infiltration, the inverse‐opal pore size can be increased with sub‐nanometer resolution and without distorting the lattice to allow for a high degree of dielectric backfilling and increased optical tunability. For a 10 % sacrificial layer, static tunability of 80 % is predicted for the inverse opal. To illustrate this technique, SiO₂ opal templates were infiltrated using atomic layer deposition of ZnS, Al₂O₃, and TiO₂. Experimentally, a static tunability of over 600 nm, or 58 %, was achieved and is well described by both a geometrical model and a numerical‐simulation algorithm. When extended to materials of higher refractive index, this method will allow the facile fabrication of 3D photonic crystals with optimized photonic bandgaps.     

Interface Functionalization of Photoelectrodes with Graphene for High Performance Dye‐Sensitized Solar Cells

The microstructures of photo‐ and counter‐electrodes play critical roles in the performance of dye‐sensitized solar cells (DSSCs). In particular, various interfaces, such as fluorinated‐tin oxide (FTO)/TiO₂, TiO₂/TiO₂, and TiO₂/electrolyte, in DSSCs significantly affect the final power conversion efficiency (PCE). However, research has generally focused more on the design of various nanostructured semiconducting materials with emphasis on optimizing chemical or/and physical properties, and less on these interface functionalizations for performance improvement. This work explores a new application of graphene to modify the interface of FTO/TiO₂ to suppress charge recombination. In combination with interfaces functionalization of TiO₂/TiO₂ for low charge‐transport resistance and high charge‐transfer rate, the final PCE of DSSC is remarkably improved from 5.80% to 8.13%, achieving the highest efficiency in comparison to reported graphene/TiO₂‐based DSSCs. The method of using graphene to functionalize the surface of FTO substrate provides a better alternative method to the conventional pre‐treatment through hydrolyzing TiCl₄ and an approach to reduce the adverse effect of microstructural defect of conducting glass substrate for electronic devices.     

High Reversible Pseudocapacity in Mesoporous Yolk–Shell Anatase TiO2/TiO2(B) Microspheres Used as Anodes for Li‐Ion Batteries

As an anode material for lithium‐ion batteries, titanium dioxide (TiO₂) shows good gravimetric performance (336 mAh g^?1 for LiTiO₂) and excellent cyclability. To address the poor rate behavior, slow lithium‐ion (Li⁺) diffusion, and high irreversible capacity decay, TiO₂ nanomaterials with tuned phase compositions and morphologies are being investigated. Here, a promising material is prepared that comprises a mesoporous “yolk–shell” spherical morphology in which the core is anatase TiO₂ and the shell is TiO₂(B). The preparation employs a NaCl‐assisted solvothermal process and the electrochemical results indicate that the mesoporous yolk–shell microspheres have high specific reversible capacity at moderate current (330.0 mAh g^?1 at C/5), excellent rate performance (181.8 mAh g^?1 at 40C), and impressive cyclability (98% capacity retention after 500 cycles). The superior properties are attributed to the TiO₂(B) nanosheet shell, which provides additional active area to stabilize the pseudocapacity. In addition, the open mesoporous morphology improves diffusion of electrolyte throughout the electrode, thereby contributing directly to greatly improved rate capacity.     

Hierarchical Double‐Shell Nanostructures of TiO2 Nanosheets on SnO2 Hollow Spheres for High‐Efficiency,Solid‐State,Dye‐Sensitized Solar Cells

A high‐energy conversion efficiency of 8.2% at 100 mW cm^?2 is reported, one of the highest values for N719‐based, solid‐state, dye‐sensitized solar cells (ssDSSCs). The solar cells are based on hierarchical double‐shell nanostructures consisting of inner SnO₂ hollow spheres (SHS) surrounded by outer TiO₂ nanosheets (TNSs). Deposition of the TNS on the SHS outer surface is performed via solvothermal reactions in order to generate a double‐shell SHS@TNS nanostructure that provides a large surface area and suppresses recombination of photogenerated electrons. An organized mesoporous (OM)‐TiO₂ film with high porosity, large pores, and good interconnectivity is also prepared via a sol‐gel process using a poly(vinyl chloride)‐g‐poly(oxyethylene methacrylate) (PVC‐g‐POEM) graft copolymer template. This film is utilized as a matrix to disperse the double‐shell nanostructures. Such nanostructures provide good pore‐filling for solid polymer electrolytes, faster electron transfer, and enhanced light scattering, as confirmed by reflectance spectroscopy, incident photon‐to‐electron conversion efficiency (IPCE), and intensity‐modulated photocurrent spectroscopy (IMPS)/intensity‐modulated photovoltage spectroscopy (IMVS).