Enhanced Performance of I2‐Free Solid‐State Dye‐Sensitized Solar Cells with Conductive Polymer up to 6.8%

An iodine‐free solid‐state dye‐sensitized solar cell (ssDSSC) is reported here, with 6.8% energy conversion efficiency—one of the highest yet reported for N719 dye—as a result of enhanced light harvesting from the increased transmittance of an organized mesoporous TiO₂ interfacial layer and the good hole conductivity of the solid‐state‐polymerized material. The organized mesoporous TiO₂ (OM‐TiO₂) interfacial layer is prepared on large‐area substrates by a sol‐gel process, and is confirmed by scanning electron microscopy (SEM) and grazing incidence small‐angle X‐ray scattering (GISAXS). A 550‐nm‐thick OM‐TiO₂ film coated on fluorine‐doped tin oxide (FTO) glass is highly transparent, resulting in transmittance increases of 8 and 4% compared to those of the bare FTO and conventional compact TiO₂ film on FTO, respectively. The high cell performance is achieved through careful control of the electrode/hole transport material (HTM) and nanocrystalline TiO₂/conductive glass interfaces, which affect the interfacial resistance of the cell. Furthermore, the transparent OM‐TiO₂ film, with its high porosity and good connectivity, exhibits improved cell performance due to increased transmittance in the visible light region, decreased interfacial resistance ( Ω ), and enhanced electron lifetime ( τ ). The cell performance also depends on the conductivity of HTMs, which indicates that both highly conductive HTM and the transparent OM‐TiO₂ film interface are crucial for obtaining high‐energy conversion efficiencies in I₂‐free ssDSSCs.     

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.     

Solid‐State Photovoltaic Thin Films using TiO2, Organic Dyes,and Layer‐by‐Layer Polyelectrolyte Nanocomposites

We report photovoltaic devices consisting of patterned TiO₂, porphyrin dyes, and layer‐by‐layer (LBL) polyelectrolyte multilayer/oligoethylene glycol dicarboxylic acid (OEGDA) composite films. A composite polyelectrolyte LBL/OEGDA film was fabricated by formation of an alternating multilayer of linear polyethyleneimine (LPEI) and polyacrylic acid (PAA), followed by immersion of the LBL film into an OEGDA aqueous solution. The ionic conductivity attained in this LBL LPEI/PAA and OEGDA composite film was approximately 10^–5 S cm^–1 at room temperature and humidity. Investigations of dye‐sensitized photovoltaic devices constructed with the LBL (LPEI/PAA)/OEGDA composite films, TiO₂, and four types of porphyrin dyes resulted in optimization of the dye molecule and its orientation at the interface with the ionically conductive composite. The photocurrent value of photovoltaic devices constructed with the composite LBL/OEGDA film from illumination of a xenon white light source exhibited a nearly 1.5 times enhancement over the device without OEGDA. This enhancement of the photocurrent was due to the high room‐temperature ionic conductivity of the multilayer composite film. Further marked improvements of the photovoltaic performance were achieved by patterning the TiO₂ electrode using polymer stamping as a template for TiO₂ deposition. The device with patterned TiO₂ electrodes exhibited almost 10 times larger conversion efficiencies than a similar device without patterning.     

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.     

Core/Shell PbSe/PbS QDs TiO2 Heterojunction Solar Cell

Quasi type‐II PbSe/PbS quantum dots (QDs) are employed in a solid state high efficiency QD/TiO₂ heterojunction solar cell. The QDs are deposited using layer‐by‐layer deposition on a half‐micrometer‐thick anatase TiO₂ nanosheet film with (001) exposed facets. Theoretical calculations show that the carriers in PbSe/PbS quasi type‐II QDs are delocalized over the entire core/shell structure, which results in better QD film conductivity compared to PbSe QDs. Moreover, PbS shell permits better stability and facile electron injection from the QDs to the TiO₂ nanosheets. To complete the electrical circuit of the solar cell, a Au film is evaporated as a back contact on top of the QDs. This PbSe/PbS QD/TiO₂ heterojunction solar cell produces a light to electric power conversion efficiency (η) of 4% with short circuit photocurrent (J_sc) of 17.3 mA/cm². This report demonstrates highly efficient core/shell near infrared QDs in a QD/TiO₂ heterojunction solar cell.     

Efficient and economical dye-sensitized solar cells based on graphene/TiO2 nanocomposite as a photoanode and graphene as a Pt-free catalyst for counter electrode

Dye-sensitized solar cells have been fabricated by employing graphene/TiO₂ nanocomposites as photoanodes and graphene as a counter electrode. The mixing technique is used to prepare graphene/TiO₂ nanocomposites. The dispersion of graphene in TiO₂ is affirmed by transmission electron microscopy analysis. X-ray photoelectron spectroscopy is carried out to confirm the interstitial incorporation of carbon atoms in the TiO₂ matrix through O TiC and TiOC surface states. The electrochemical activity and stability of graphene as a catalyst for counter electrode are investigated by cyclic voltammetry and chronoamperometry measurements. Solar cells fabricated are characterized by photocurrent–voltage characteristic, Incident photon-to-current efficiency, and electrochemical impedance spectroscopy analyses. The solar cell assembled with 0.08%GR-TiO₂/N3/GR shows power conversion efficiency of 7.70%. This efficiency is superior to that of TiO₂/N3/Pt based solar cell (7.28%). The improvement in efficiency can be attributed to a fast electron transport, improved light harvesting efficiency, and enhanced electron collection at photoanodes.     

Improved power conversion efficiency by insertion of RGO–TiO2 composite layer as optical spacer in polymer bulk heterojunction solar cells

We report that the power conversion efficiency (PCE) can be enhanced in polymer bulk heterojunction solar cells by inserting an interfacial electron transporting layer consisting of pristine TiO₂ or reduced graphene oxide–TiO₂ (RGO–TiO₂) between the active layer and cathode Al electrode. The enhancement in the PCE has been analyzed through the optical absorption, current–voltage characteristics under illumination and estimation of photo-induced charge carrier generation rate. It was found that either TiO₂ or RGO–TiO₂ interfacial layers improve the light harvesting, as well as the charge extraction efficiency, acting as a blocking layer for holes, and also reducing charge recombination. The combined enhancement in light harvesting property and charge collection efficiency improves the PCE of the organic solar cell up to 4.18% and 5.33% for TiO₂ and RGO–TiO₂ interfacial layer, respectively, as compared to a value of 3.26% for the polymer solar cell without interfacial layer.     

Honeycomb‐Like Organized TiO2 Photoanodes with Dual Pores for Solid‐State Dye‐Sensitized Solar Cells

A solid‐state dye‐sensitized solar cell (ssDSSC) with 7.4% efficiency at 100 mW/cm² is reported. This efficiency is one of the highest observed for N719 dye. High performance is achieved via a honeycomb‐like, organized mesoporous TiO₂ photoanode with dual pores, high porosity, good interconnectivity, and excellent light scattering properties. The TiO₂ photoanodes are prepared without any TiCl₄ treatment via a one‐step, direct self‐assembly of hydrophilically preformed TiO₂ nanocrystals and poly(vinyl chloride)‐g‐poly(oxyethylene methacrylate) (PVC‐g‐POEM) graft copolymer as a titania source and a structure‐directing agent, respectively. Upon controlling the secondary forces between the polymer/TiO₂ hybrid and the solvent by varying the amounts of HCl/H₂O mixture or toluene, honeycomb‐like structures are generated to improve light scattering properties. Such multifunctional nanostructures with dual pores provide good pore‐filling of solid polymer electrolyte with large volume, enhanced light harvesting and reduced charge recombination, as confirmed by reflectance spectroscopy, incident photon‐to‐electron conversion efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) analysis.     

Band gap engineering and modifying surface of TiO2 nanostructures by Fe2O3 for enhanced-performance of dye sensitized solar cell

Well-crystallized Fe₂O₃-modified TiO₂ nanoparticles are prepared by a hydrothermal method and were successfully used as the photoanode of dye-sensitized solar cell (DSSC). Structural, optical and thermal characterizations were carried out by SEM, XRD, AFM, EDAX, DTG, TG and UV–vis spectroscopy. We show that the solar conversion efficiency, incident photocurrent efficiency (IPCE) and fill factor (FF) of Fe₂O₃-modified TiO₂ are significantly increased, about 40%, compared those of to bare TiO₂. DSSC shows power conversion efficiency of 7.27% based on Fe₂O₃-modified TiO₂ while TiO₂ anatase shows 5.10% solar conversion efficiency. The high improvement in cell performance is attributed to the enhanced light harvesting and high specific surface area for adsorbing more dye molecules in Fe₂O₃-modified TiO₂ nanostructures.     

All‐Solution‐Processed Indium‐Free Transparent Composite Electrodes based on Ag Nanowire and Metal Oxide for Thin‐Film Solar Cells

Fully solution‐processed Al‐doped ZnO/silver nanowire (AgNW)/Al‐doped ZnO/ZnO multi‐stacked composite electrodes are introduced as a transparent, conductive window layer for thin‐film solar cells. Unlike conventional sol–gel synthetic pathways, a newly developed combustion reaction‐based sol–gel chemical approach allows dense and uniform composite electrodes at temperatures as low as 200 °C. The resulting composite layer exhibits high transmittance (93.4% at 550 nm) and low sheet resistance (11.3 Ω sq^‐1), which are far superior to those of other solution‐processed transparent electrodes and are comparable to their sputtered counterparts. Conductive atomic force microscopy reveals that the multi‐stacked metal‐oxide layers embedded with the AgNWs enhance the photocarrier collection efficiency by broadening the lateral conduction range. This as‐developed composite electrode is successfully applied in Cu(In_1‐x,Ga_x)S₂ (CIGS) thin‐film solar cells and exhibits a power conversion efficiency of 11.03%. The fully solution‐processed indium‐free composite films demonstrate not only good performance as transparent electrodes but also the potential for applications in various optoelectronic and photovoltaic devices as a cost‐effective and sustainable alternative electrode.     

Plasmonic Au/TiO2‐Dumbbell‐On‐Film Nanocavities for High‐Efficiency Hot‐Carrier Generation and Extraction

Plasmon‐induced hot carriers have vast potential for light‐triggered high‐efficiency carrier generation and extraction, which can overcome the optical band gap limit of conventional semiconductor‐based optoelectronic devices. Here, it is demonstrated that Au/TiO₂ dumbbell nanostructures assembled on a thin Au film serve as an efficient optical absorber and a hot‐carrier generator in the visible region. Upon excitation of localized surface plasmons in such coupled particle‐on‐film nanocavities, the energetic conduction electrons in Au can be injected over the Au/TiO₂ Schottky barrier and migrated to TiO₂, participating in the chemical reaction occurring at the TiO₂ surface. Compared with the same dumbbell nanostructures on an indium tin oxide (ITO) film, such nanocavities exhibit remarkable enhancement in both photocurrent amplitude and reaction rate that arise from increased light absorption and near‐field amplification in the presence of the Au film. The incident‐wavelength‐dependent photocurrent and reaction rate measurements jointly reveal that Au‐film‐mediated near‐field localization facilitates more efficient electron–hole separation and transport in the dumbbells and also promotes strong d‐band optical transitions in the Au film for generation of extra hot electrons. Such nanocavities provide a new plasmonic platform for effective photoexcitation and extraction of hot carriers and also better understanding of their fundamental science and technological implications in solar energy harvesting.     

Carbon/carbon nanocomposites as counter electrodes for platinum free dye-sensitized solar cells

In this work, carbonaceous materials and their combinations with each other were used as counter electrodes for efficient dye-sensitized solar cells (DSSCs). A small amount of TiO₂ paste was also incorporated in each electrocatalyst to increase the adhesion between the carbon material and the conductive glass substrate. The dispersion of carbonaceous materials in composite films was characterized by transmission electron microscopy (TEM). Electrocatalytic characteristics of carbon/carbon catalysts are systematically investigated by electrochemical techniques, such as cyclic voltammetry and chronoamperometry. Solar cells assembled with carbon/carbon composite counter electrodes were characterized by photocurrent–voltage characteristic and electrochemical impedance spectroscopy measurements. The results indicate that under optimal conditions, the solar cell assembled with carbon/carbon composite counter electrode containing activated carbon, multi-walled carbon nanotube and graphene, shows power conversion efficiency of 10.73%. This photovoltaic performance is comparable with 11.20% for the platinum-based dye-sensitized solar cell. The results exhibit that carbonaceous material is an encouraging alternative for low-cost DSSCs.     

Self‐Assembly of Flexible Free‐Standing 3D Porous MoS2‐Reduced Graphene Oxide Structure for High‐Performance Lithium‐Ion Batteries

Flexible freestanding electrodes are highly desired to realize wearable/flexible batteries as required for the design and production of flexible electronic devices. Here, the excellent electrochemical performance and inherent flexibility of atomically thin 2D MoS₂ along with the self‐assembly properties of liquid crystalline graphene oxide (LCGO) dispersion are exploited to fabricate a porous anode for high‐performance lithium ion batteries. Flexible, free‐standing MoS₂–reduced graphene oxide (MG) film with a 3D porous structure is fabricated via a facile spontaneous self‐assembly process and subsequent freeze‐drying. This is the first report of a one‐pot self‐assembly, gelation, and subsequent reduction of MoS₂/LCGO composite to form a flexible, high performance electrode for charge storage. The gelation process occurs directly in the mixed dispersion of MoS₂ and LCGO nanosheets at a low temperature (70 °C) and normal atmosphere (1 atm). The MG film with 75 wt% of MoS₂ exhibits a high reversible capacity of 800 mAh g^?1 at a current density of 100 mA g^?1. It also demonstrates excellent rate capability, and excellent cycling stability with no capacity drop over 500 charge/discharge cycles at a current density of 400 mA g^?1.     

Ionic Liquid‐Assisted Synthesis of TiO2–Carbon Hybrid Nanostructures for Lithium‐Ion Batteries

Building nanocomposite architectures based on nanocarbon materials (such as carbon nanotubes and graphene nanosheets) and metal‐oxide nanoparticles is of great interests for electrochemical energy storage. Here, an ionic‐liquid‐assisted strategy is presented to mediate the in situ growth of TiO₂ nanocrystals with controlled size on carbon nanotubes and graphene, and also reduce the modified carbon supports to recover the graphitic structure simultaneously. The as‐prepared nanocomposites exhibit a highly porous and robust structure with intimate coupling between TiO₂ nanocrystals and carbon supports, which offers facile ion and electron transport pathway as well as high mechanical stability. When evaluated as electrode materials for lithium‐ion batteries, the nanocomposites manifest high specific capacity, long cycling lifetime, and excellent rate capability, showing their promising application in high‐performance energy storage devices.     

Efficient dye-sensitized solar cells based on CNTs and Zr-doped TiO2 nanoparticles

The light scattering, harvesting and adsorption effects in dye-sensitized solar cells (DSSCs) are studied by preparation of coated carbon nanotubes (CNTs) with TiO₂ and Zr-doped TiO₂ nanoparticles in the forms of mono- and double-layer cells. X-ray diffraction (XRD) analysis reveals that the phase composition of Zr-doped TiO₂ electrode is a mixture of anatase and rutile phases with major rutile content, whereas it is the same mixture with major anatase content for coated CNTs with TiO₂. Furthermore, the average crystallite size of Zr-doped TiO₂ electrode is slightly decreased with Zr introduction. Field emission scanning electron microscope (FE-SEM) images show that the porosity of Zr-doped TiO₂ electrodes is higher than that of undoped electrode, enhancing dye adsorption. UV–visible spectroscopy analysis reveals that the absorption onset of Zr-doped TiO₂ electrodes is slightly shifted to longer wavelength (the red-shift) in comparison with that of undoped TiO₂ electrode. Moreover, the band gap energy of TiO₂ nanoparticles is decreased by Zr introduction, enhancing light absorption. It is found that electron injection of monolayer TiO₂ electrode is improved by introduction of 0.025 mol% Zr, resulted in enhancement of its power conversion efficiency (PCE) up to 6.81% compared with 6.17% for pure TiO₂ electrode. Moreover, electron transport and light scattering are enhanced by incorporation of 0.025 wt% coated CNTs with TiO₂ in the over-layer of double layer electrode. Therefore, double layer solar cell composed of 0.025 mol% Zr-doped TiO₂ nanoparticles as the under-layer and mixtures of these nanoparticles and 0.025 wt% coated CNTs with TiO₂ as the over-layer shows the highest PCE of 8.19%.     

Rapid Fabrication of an Inverse Opal TiO2 Photoelectrode for DSSC Using a Binary Mixture of TiO2 Nanoparticles and Polymer Microspheres

A rapid fabrication method of highly reflective TiO₂ inverse opal (IO) film exhibiting controllable thickness, high TiO₂ content, and excellent interfacial contact with glass substrate is presented. By inducing accelerated solvent evaporation during the colloidal self‐assembly process, a composite film of polystyrene (PS)/TiO₂ has been directly fabricated on a fluorine doped tin oxide (FTO) glass substrate, which exhibits the highly ordered opaline structure of PS embedded into the TiO₂ matrix. This hybrid fabrication path leads to the formation of layers with the preferred {111} face‐centered cubic (FCC) orientation parallel to the substrate and to produce a 1 cm²‐wide well‐ordered composite colloidal crystal film in less than 30 min. The film showed highly ordered FCC structure, particularly at the upper region, due to the induced solvent evaporation and exhibited a reliable light modulation at a reflectance mode. Regardless of the size of sacrificial PS microspheres, TiO₂ IO films of controllable thickness were successfully formed by varying the moving speed of the fabrication cell. The binary aqueous dispersion of tailor‐made anatase TiO₂ nanoparticles and monodisperse PS microspheres showed a high degree of dispersion stability under basic conditions. Hydrothermal treatment of the TiO₂ dispersion favored the crystallinity of the coated film and provided small volume contraction after thermal calcinations. The high degree of dispersion stability enabled to increase TiO₂ content in a binary mixture, which is more favorable toward the robust and large‐area IO film. The calcined films exhibited excellent mechanical robustness and intimate interfacial contact with the glass substrate. which in turn resulted in higher TiO₂ content near the glass substrate. The TiO₂ IO film was tested as a dye‐sensitized solar cell (DSSC) photoelectrode, and a single cell showed a relatively high photon‐to‐current conversion efficiency of 4.2%. The high TiO₂ content of IO film and its good adhesion to the FTO subratrate remarkably improved in the performance of the solar cell compared to the previous investigations where post‐infiltration of TiO₂ had been employed.     

Constraining Si Particles within Graphene Foam Monolith: Interfacial Modification for High‐Performance Li+ Storage and Flexible Integrated Configuration

Pulverization of electrode materials and loss of electrical contact have been identified as the major causes for the performance deterioration of alloy anodes in Li‐ion batteries. This study presents the hierarchical arrangement of spatially confining silicon nanoparticles (Si NPs) within graphene foam (GF) for alleviating these issues. Through a freeze‐drying method, the highly oriented GF monolith is engineered to fully encapsulate the Si NPs, serving not only as a robust framework with the well‐accessible thoroughfares for electrolyte percolation but also a physical blocking layer to restrain Si from direct exposure to the electrolyte. In return, the pillar effect of Si NPs prevents the graphene sheets from restacking while preserving the highly efficient electron/Li⁺ transport channels. When evaluated as a binder‐free anode, impressive cycle performance is realized in both half‐cell and full‐cell configurations. Operando X‐ray diffraction and in‐house X‐ray photoelectron spectroscopy confirm the pivotal protection of GF to sheathe the most volume‐expanded lithiated phase (Li₁₅Si₄) at room temperature. Furthermore, a free‐standing composite film is developed through readjusting the pore size in GF/Si monolith and directly integrated with nanocellulose membrane (NCM) separator. Because of the good electrical conductivity and structural integrity of the GF monolith as well as the flexibility of the NCM separator, the as‐developed GF/Si‐NCM electrode showcases the potential use in the flexible electronic devices.     

Enhancing current density of perovskite solar cells using TiO2-ZrO2 composite scaffold layer

A novel scaffold layer composed of TiO₂-ZrO₂ composite was fabricated for perovskite solar cell. Compared with pure TiO₂ nanoparticles (NPs), the relatively larger ZrO₂ NPs could increase film roughness and enhance light-scattering effect in TiO₂-ZrO₂ composite films. The device exhibited outstanding power conversion efficiency (PCE) of 11.41%. The morphology and aggregation of particles, three-dimensional roughness, as well as the ingredient and micro-structure of FTO/compact TiO₂/TiO₂-ZrO₂ was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD), respectively. Moreover, the optical property of TiO₂-ZrO₂ films for visible light was characterized by UV–visible absorption spectroscopy (UV–vis), and its influence on quantum yield of the device was further demonstrated by incident photon-to-electron conversion efficiency (IPCE). Owing to the inert oxide, the short-circuit current density of perovskite solar cell using TiO₂-ZrO₂ composition as scaffold layer increased by 21% compared to the one employing pure TiO₂ mesoporous film.     

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.     

Solar Water Splitting by TiO2/CdS/Co–Pi Nanowire Array Photoanode Enhanced with Co–Pi as Hole Transfer Relay and CdS as Light Absorber

The cobalt phosphate water oxidation catalyst (Co–Pi WOC) stabilized, CdS sensitized TiO₂ nanowire arrays for nonsacrificial solar water splitting are reported. In this TiO₂/CdS/Co–Pi photoanode, the Co–Pi WOC acts as hole transfer relay to accelerate the surface water oxidation reaction, CdS serves as light absorber for wider solar spectra harvesting, and TiO₂ matrix provides direct pathway for electron transport. This triple TiO₂/CdS/Co–Pi hybrid photoanode exhibits much enhanced photocurrent density and negatively shifts in onset potential, resulting in 1.5 and 3.4 times improved photoconversion efficiency compared to the TiO₂/CdS and TiO₂ photoanode, respectively. More importantly, the TiO₂/CdS/Co–Pi shows significantly improved photoelectrochemical stability compared to the TiO₂/CdS electrode, with ≈72% of the initial photocurrent retained after 2 h irradiation. The reason for the promoted performance is discussed in detail based on electrochemical measurements. This work provides a new paradigm for designing 1D nanoframework/light absorber/WOC photoanode to simultaneously enhance light absorption, charge separation, and transport and surface water oxidation reaction for efficient and stable solar fuel production.