Influences of Acid on Molecular Forms of Fluorescein and Photoinduced Electron Transfer in Fluorescein‐Dispersing Sol–Gel Titania Films

Fluorescein‐dispersing titania gel films were prepared by the acid‐catalyzed sol–gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid–base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate‐like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye–titania complex. This result indicated that the dianion form was the most favorable for formation of the dye–titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye–titania complex formation played an important role in the electron injection from the dye to the titania conduction band.     

Molecular design of organic dyes with diketopyrrolopyrrole for dye‐sensitized solar cell: A theoretical approach

Three designed metal‐free dyes based on 3‐(10‐butyl‐8‐(methylthio)‐10H‐phenothiazin‐3‐yl)‐2‐cyanoacrylic acid (V5) are investigated by density functional theory (DFT) and time‐dependent DFT to improve the efficiency of V5‐based solar cell devices. We have studied the geometrical structures, excitations, electronic structures, and conduction band shift caused by dye adsorption. The results indicate that the designed dyes have several merits compared with V5 including: (i) smaller energy band gaps and the LUMO closer to conduction band of TiO₂; (ii) wider absorption spectra and higher oscillator strength; (iii) larger dipole moment that lead to higher V_oc value. Our work suggests that the modification of π‐bridge with diketopyrrolopyrrole unit is very effective for designing novel metal‐free dyes with improved performance for dye‐sensitized solar cells (DSSCs). These findings are expected to provide a bright way to design new efficient metal‐free organic DSSCs. © 2014 Wiley Periodicals, Inc.     

The Origin of Higher Open‐Circuit Voltage in Zn‐Doped TiO2 Nanoparticle‐Based Dye‐Sensitized Solar Cells

Zn‐doped anatase TiO₂ nanoparticles are synthesized by a one‐step hydrothermal method. Detailed electrochemical measurements are undertaken to investigate the origin of the effect of Zn doping on the performance of dye‐sensitized solar cells (DSSCs). It is found that incorporation of Zn²⁺ into an anatase lattice elevates the edge of the conduction band (CB) of the photoanodes and the Fermi level is shifted toward the CB edge, which contributes to the improvement in open‐circuit voltage (V_OC). Charge‐density plots across the cell voltage further confirm the increase in the CB edge in DSSCs directly. Photocurrent and transient photovoltage measurements are employed to study transport and recombination dynamics. The electron recombination is accelerated at higher voltages close to the CB edge, thus leading to a negative effect on the V_OC.     

Controlling Interfacial Recombination in Aqueous Dye‐Sensitized Solar Cells by Octadecyltrichlorosilane Surface Treatment

A general and convenient strategy is proposed for enhancing photovoltaic performance of aqueous dye‐sensitized solar cells (DSCs) through the surface modification of titania using an organic alkyl silane. Introduction of octadecyltrichlorosilane on the surface of dyed titania photoanode as an organic barrier layer leads to the efficient suppression of electron recombination with oxidized cobalt species by restricting access of the cobalt redox couple to the titania surface. The champion ODTS‐treated aqueous DSCs (0.25 mM ODTS in hexane for 5 min) exhibit a V_oc of 821±4 mV and J_sc of 10.17±0.21 mA cm^?2, yielding a record PCE of 5.64±0.10 %. This surface treatment thus serves as a promising post‐dye strategy for improving the photovoltaic performance of other aqueous DSCs.     

Constructing Organic D–A–π‐A‐Featured Sensitizers with a Quinoxaline Unit for High‐Efficiency Solar Cells: The Effect of an Auxiliary Acceptor on the Absorption and the Energy Level Alignment

Four organic D–A –π‐A‐featured sensitizers (TQ1, TQ2, IQ1, and IQ2) have been studied for high‐efficiency dye‐sensitized solar cells (DSSCs). We employed an indoline or a triphenylamine unit as the donor, cyanoacetic acid as the acceptor/anchor, and a thiophene moiety as the conjugation bridge. Additionally, an electron‐withdrawing quinoxaline unit was incorporated between the donor and the π‐conjugation unit. These sensitizers show an additional absorption band covering the broad visible range in solution. The contribution from the incorporated quinoxaline was investigated theoretically by using DFT and time‐dependent DFT. The incorporated low‐band‐gap quinoxaline unit as an auxiliary acceptor has several merits, such as decreasing the band gap, optimizing the energy levels, and realizing a facile structural modification on several positions in the quinoxaline unit. As demonstrated, the observed additional absorption band is favorable to the photon‐to‐electron conversion because it corresponds to the efficient electron transitions to the LUMO orbital. Electrochemical impedance spectroscopy (EIS) Bode plots reveal that the replacement of a methoxy group with an octyloxy group can increase the injection electron lifetime by a factor of 2.4. IQ2 and TQ2 can perform well without any co‐adsorbent, successfully suppress the charge recombination from TiO₂ conduction band to I₃^? in the electrolyte, and enhance the electron lifetime, resulting in a decreased dark current and enhanced open circuit voltage (V_oc) values. By using a liquid electrolyte, DSSCs based on dye IQ2 exhibited a broad incident photon‐to‐current conversion efficiency (IPCE) action spectrum and high efficiency (η=8.50 %) with a short circuit current density (J_sc) of 15.65 mA cm^?2, a V_oc value of 776 mV, a fill factor (FF) of 0.70 under AM 1.5 illumination (100 mW cm^?2). Moreover, the overall efficiency remained at 97 % of the initial value after 1000 h of visible‐light soaking.     

Molecular Engineering of Simple Phenothiazine‐Based Dyes To Modulate Dye Aggregation,Charge Recombination,and Dye Regeneration in Highly Efficient Dye‐Sensitized Solar Cells

A series of simple phenothiazine‐based dyes, namely, TP , EP , TTP , ETP , and EEP have been developed, in which the thiophene (T), ethylenedioxythiophene (E), their dimers, and mixtures are present to modulate dye aggregation, charge recombination, and dye regeneration for highly efficient dye‐sensitized solar cell (DSSC) applications. Devices sensitized by the dyes TP and TTP display high power conversion efficiencies (PCEs) of 8.07 (J_sc=15.2 mA cm^?2, V_oc=0.783 V, fill factor (FF)=0.679) and 7.87 % (J_sc=16.1 mA cm^?2, V_oc=0.717 V, FF=0.681), respectively; these were measured under simulated AM 1.5 sunlight in conjunction with the I^?/I₃^? redox couple. By replacing the T group with the E unit, EP ‐based DSSCs had a slightly lower PCE of 7.98 % with a higher short‐circuit photocurrent (J_sc) of 16.7 mA cm^?2. The dye ETP , with a mixture of E and T, had an even lower PCE of 5.62 %. Specifically, the cell based on the dye EEP , with a dimer of E, had inferior J_sc and V_oc values and corresponded to the lowest PCE of 2.24 %. The results indicate that the photovoltaic performance can be finely modulated through structural engineering of the dyes. The selection of T analogues as donors can not only modulate light absorption and energy levels, but also have an impact on dye aggregation and interfacial charge recombination of electrons at the interface of titania, electrolytes, and/or oxidized dye molecules; this was demonstrated through DFT calculations, electrochemical impedance analysis, and transient photovoltage studies.     

Structurally Stabilized Organosilane‐Templated Thermostable Mesoporous Titania

Structurally thermostable mesoporous anatase TiO₂ (m‐TiO₂) nanoparticles, uniquely decorated with atomically dispersed SiO₂, is reported for the first time. The inorganic Si portion of the novel organosilane template, used as a mesopores‐directing agent, is found to be incorporated in the pore walls of the titania aggregates, mainly as isolated sites. This is evident by transmission electron microscopy and high‐angle annular dark field scanning transmission electron microscopy, combined with electron dispersive X‐ray spectroscopy. This type of unique structure provides exceptional stability to this new material against thermal collapse of the mesoporous structure, which is reflected in its high surface area (the highest known for anatase titania), even after high‐temperature (550 °C) calcination. Control of crystallite size, pore diameter, and surface area is achieved by varying the molar ratios of the titanium precursor and the template during synthesis. These mesoporous materials retain their porosity and high surface area after template removal and further NaOH/HCl treatment to remove silica. We investigate their performance for dye‐sensitized solar cells (DSSCs) with bilayer TiO₂ electrodes, which are prepared by applying a coating of m‐TiO₂ onto a commercial titania (P25) film. The high surface area of the upper mesoporous layer in the P25–m‐TiO₂ DSSC significantly increases the dye loading ability of the photoanode. The photocurrent and fill factor for the DSSC with the bilayer TiO₂ electrode are greatly improved. The large increase in photocurrent current (ca. 56 %) in the P25–m‐TiO₂ DSSC is believed to play a significant role in achieving a remarkable increase in the photovoltaic efficiency (60 %) of the device, compared to DSSCs with a monolayer of P25 as the electrode.     

Dyes and Redox Couples with Matched Energy Levels: Elimination of the Dye‐Regeneration Energy Loss in Dye‐Sensitized Solar Cells

In dye‐sensitized solar cells (DSSCs), a significant dye‐regeneration force (ΔG_reg⁰≥0.5 eV) is usually required for effective dye regeneration, which results in a major energy loss and limits the energy‐conversion efficiency of state‐of‐art DSSCs. We demonstrate that when dye molecules and redox couples that possess similar conjugated ligands are used, efficient dye regeneration occurs with zero or close‐to‐zero driving force. By using Ru(dcbpy)(bpy)₂²⁺ as the dye and Ru(bpy)₂(MeIm)₂^3+//2+ as the redox couple, a short‐circuit current (J_sc) of 4 mA cm^?2 and an open‐circuit voltage (V_oc) of 0.9 V were obtained with a ΔG_reg⁰ of 0.07 eV. The same was observed for the N3 dye and Ru(bpy)₂(SCN)₂^1+/0 (ΔG_reg⁰=0.0 eV), which produced an J_sc of 2.5 mA cm^?2 and V_oc of 0.6 V. Charge recombination occurs at pinholes, limiting the performance of the cells. This proof‐of‐concept study demonstrates that high V_oc values can be attained by significantly curtailing the dye‐regeneration force.     

Investigation of Electron Behavior in Nano‐TiO2 Photocatalysis by Using In Situ Open‐Circuit Voltage and Photoconductivity Measurements

The in situ open‐circuit voltages (V_oc) and the in situ photoconductivities have been measured to study electron behavior in photocatalysis and its effect on the photocatalytic oxidation of methanol. It was observed that electron injection to the conduction band (CB) of TiO₂ under light illumination during photocatalysis includes two sources: from the valence band (VB) of TiO₂ and from the methanol molecule. The electron injection from methanol to TiO₂ is slower than that directly from the VB, which indicates that the adsorption mode of methanol on the TiO₂ surface can change between dark and illuminated states. The electron injection from methanol to the CB of TiO₂ leads to the upshift of the Fermi level of electrons in TiO₂, which is the thermodynamic driving force of photocatalytic oxidation. It was also found that the charge state of nano‐TiO₂ is continuously changing during photocatalysis as electrons are injected from methanol to TiO₂. Combined with the apparent Langmuir–Hinshelwood kinetic model, the relation between photocatalytic kinetics and electrons in the TiO₂ CB was developed and verified experimentally. The photocatalytic rate constant is the variation of the Fermi level with time, based on which a new method was developed to calculate the photocatalytic kinetic rate constant by monitoring the change of V_oc with time during photocatalysis.     

Characterizing the Role of Iodine Doping in Improving Photovoltaic Performance of Dye‐Sensitized Hierarchically Structured ZnO Solar Cells

We report two novel types of hierarchically structured iodine‐doped ZnO (I? ZnO)‐based dye‐sensitized solar cells (DSCs) using indoline D205 and the ruthenium complex N719 as sensitizers. It was found that iodine doping boosts the efficiencies of D205 I? ZnO and N719 I? ZnO DSCs with an enhancement of 20.3 and 17.9 %, respectively, compared to the undoped versions. Transient absorption spectra demonstrated that iodine doping impels an increase in the decay time of I? ZnO, favoring enhanced exciton life. Mott–Schottky analysis results indicated a negative shift of the flat‐band potential (V_fb) of ZnO, caused by iodine doping, and this shift correlated with the enhancement of the open circuit voltage (V_oc). To reveal the effect of iodine doping on the effective separation of e^?‐h⁺ pairs which is responsible for cell efficiency, direct visualization of light‐induced changes in the surface potential between I? ZnO particles and dye molecules were traced by Kelvin probe force microscopy. We found that potential changes of iodine‐doped ZnO films by irradiation were above one hundred millivolts and thus significantly greater. In order to correlate enhanced cell performance with iodine doping, electrochemical impedance spectroscopy, incident‐photon‐current efficiency, and cyclic voltammetry investigations on I? ZnO cells were carried out. The results revealed several favorable features of I? ZnO cells, that is, longer electron lifetime, lower charge‐transfer resistance, stronger peak current, and extended visible light harvest, all of which serve to promote cell performance.     

The effects of pyridine derivative additives on interface processes at nanocrystalline TiO2 thin film in dye‐sensitized solar cells

2‐Methyl‐4‐propoxypyridine, a new pyridine derivative, has been synthesized and used as an additive in the liquid electrolyte of dye‐sensitized solar cells (DSSCs). Compared with 2‐methylpyridne and 4‐tert‐pyridine, they were employed to study the influence of the pyridine derivative additives on the rate of recombination at the electrode/dye/electrolyte interfaces and band edge shift of TiO₂, which were measured by time‐resolved mid‐infrared absorption spectroscopy and Mott–Schottky analysis, respectively. It was found that the rate of interfacial charge recombination was enhanced when the pyridine derivative additives were present in the electrolyte. Meanwhile, the additives caused a negative shift of the band edge. However, the net effect of pyridine derivative addition was to improve the open‐circuit photovoltage according to the photoelectrochemical measurement, indicating that negative shift of conduction band of TiO₂ was a predominant factor in improving the open‐circuit photovoltage. Also, the result was strongly supported by the dark current measurement. Therefore, it provides a microscopic account for the function of the pyridine derivative additives on the open‐circuit photovoltage enhancement of the DSSCs. Furthermore, the decrease of the short‐circuit photocurrent of the cells was also attributed to the slower dye regeneration due to the addition of additives from the results of cyclic voltammetry measurement. Copyright © 2007 John Wiley & Sons, Ltd.     

Cyclometalated Ruthenium(II) Complexes Featuring Tridentate Click‐Derived Ligands for Dye‐Sensitized Solar Cell Applications

A series of heteroleptic bis(tridentate) Ru^II complexes featuring N^C^N‐cyclometalating ligands is presented. The 1,2,3‐triazole‐containing tridentate ligands are readily functionalized with hydrophobic side chains by means of click chemistry and the corresponding cyclometalated Ru^II complexes are easily synthesized. The performance of these thiocyanate‐free complexes in a dye‐sensitized solar cell was tested and a power conversion efficiency (PCE) of up to 4.0 % (J_sc=8.1 mA cm^?2, V_oc=0.66 V, FF=0.70) was achieved, while the black dye ((NBu₄)₃[Ru(Htctpy)(NCS)₃]; Htctpy=2,2′:6′,2′′‐terpyridine‐4′‐carboxylic acid‐4,4′′‐dicarboxylate) showed 5.2 % (J_sc=10.7 mA cm^?2, V_oc=0.69 V, FF=0.69) under comparable conditions. When co‐adsorbed with chenodeoxycholic acid, the PCE of the best cyclometalated dye could be improved to 4.5 % (J_sc=9.4 mA cm^?2, V_oc=0.65 V, FF=0.70). The PCEs correlate well with the light‐harvesting capabilities of the dyes, while a comparable incident photon‐to‐current efficiency was achieved with the cyclometalated dye and the black dye. Regeneration appeared to be efficient in the parent dye, despite the high energy of the highest occupied molecular orbital. The device performance was investigated in more detail by electrochemical impedance spectroscopy. Ultimately, a promising Ru^II sensitizer platform is presented that features a highly functionalizable “click”‐derived cyclometalating ligand.     

Photoelectrochemical Complexes of Fucoxanthin‐Chlorophyll Protein for Bio‐Photovoltaic Conversion with a High Open‐Circuit Photovoltage

Open‐circuit photovoltage (V_oc ) is among the critical parameters for achieving an efficient light‐to‐charge conversion in existing solar photovoltaic devices. Natural photosynthesis exploits light‐harvesting chlorophyll (Chl) protein complexes to transfer sunlight energy efficiently. We describe the exploitation of photosynthetic fucoxanthin‐chlorophyll protein (FCP) complexes for realizing photoelectrochemical cells with a high V_oc . An antenna‐dependent photocurrent response and a V_oc up to 0.72 V are observed and demonstrated in the bio‐photovoltaic devices fabricated with photosynthetic FCP complexes and TiO₂ nanostructures. Such high V_oc is determined by fucoxanthin in FCP complexes, and is rarely found in photoelectrochemical cells with other natural light‐harvesting antenna. We think that the FCP‐based bio‐photovoltaic conversion will provide an opportunity to fabricate environmental benign photoelectrochemical cells with high V_oc , and also help improve the understanding of the essential physics behind the light‐to‐charge conversion in photosynthetic complexes.     

An Azulene‐Containing Low Bandgap Small Molecule for Organic Photovoltaics with High Open‐Circuit Voltage

A simple azulene‐containing squaraine dye ( AzUSQ ) showing bandgap of 1.38 eV and hole mobility up to 1.25×10^?4 cm² V^?1 s^?1 was synthesized. With its low bandgap, an organic photovoltaic (OPV) device based on it has been made that exhibits an impressive open‐circuit voltages (V_oc) of 0.80 V. Hence, azulene might be a promising structural unit to construct OPV materials with simultaneous low bandgap, high hole mobility and high V_oc.     

Influence of Solvent and Bridge Structure in Alkylthio‐Substituted Triphenylamine Dyes on the Photovoltaic Properties of Dye‐Sensitized Solar Cells

Three new triphenylamine dyes that contain alkylthio‐substituted thiophenes with a low bandgap as a π‐conjugated bridge unit were designed and synthesized for organic dye‐sensitized solar cells (DSSCs). The effects of the structural differences in terms of the position, number, and shape of the alkylthio substituents in the thiophene bridge on the photophysical properties of the dye and the photovoltaic performance of the DSSC were investigated. The introduction of an alkylthio substituent at the 3‐position of thiophene led to a decrease in the degree of redshift and the value of the molar extinction coefficient of the charge‐transfer band, and the substituent with a bridged structure led to a larger redshift than that of the open‐chain structure. The introduction of bulky and hydrophobic side chains decreased the short‐circuit photocurrent (J_sc), which was caused by the reduced amount of dye adsorbed on TiO₂. This resulted in a decrease in the overall conversion efficiency (η), even though it could improve the open‐circuit voltage (V_oc) due to the retardation of charge recombination. Furthermore, the change in solvents for TiO₂ sensitization had a critical effect on the performance of the resulting DSSCs due to the different amounts of dye adsorbed. Based on the optimized dye bath and molecular structure, the ethylene dithio‐substituted dye ( ATT3 ) showed a prominent solar‐to‐electricity conversion efficiency of 5.20 %.     

Low‐cost Nickel Complex Dye‐sensitized Titania Nanoparticle/nanotube Composites for Solar Cells

In this work, high‐performance dye‐sensitized solar cells (DSSCs) based on new low‐cost visible nickel complex dye (VisDye), TiO₂ nanoparticle/nanotube composites electrodes, carbon nanoparticles counter electrodes, and ionic liquids electrolytes have been fabricated. The electronic structure, optical spectroscopy, and electrochemical properties of the VisDye were studied. Experimental results indicate that it is beneficial to improve the electron transport and power conversion efficiency using the nickel complex VisDye and TiO₂ nanoparticle/nanotube composites. Under optimized conditions, the solar energy conversion efficiencies were measured. The short‐circuit current density (J_SC), the open‐circuit voltage (V_OC), the fill factor (FF), and the overall efficiency (η) of the DSSCs are 10.01 mA/cm², 516 mV, 0.68, and 3.52%, respectively. This study demonstrates that the combination of new VisDye with TiO₂ nanoparticle/nanotube composites electrodes and carbon nanoparticles counter electrodes provide a way to fabricate highly efficient dye‐sensitized solar cells in low‐cost production.     

Enhanced Performance of Quasi‐Solid‐State Dye‐Sensitized Solar Cells by Branching the Linear Substituent in Sensitizers Based on Thieno[3,4‐c]pyrrole‐4,6‐dione

Thieno[3,4‐c]pyrrole‐4,6‐dione‐based organic sensitizers with triphenylamine ( FNE38 and FNE40 ) or julolidine ( FNE39 and FNE41 ) as electron‐donating unit have been designed and synthesized. A linear hexyl group or a branched alkyl chain, the 2‐ethylhexyl group, is incorporated into molecular skeleton of the dyes to minimize intermolecular interactions. The absorption, electrochemical, and photovoltaic properties for these sensitizers were then systematically investigated. It is found that the sensitizers have similar photophysical and electrochemical properties, such as absorption spectra and energy levels, owing to their close chemical structures. However, the quasi‐solid‐state dye‐sensitized solar cells (DSSCs) based on the two types of sensitizers exhibit very different performance parameters. Upon the incorporation of the short ethyl group on the hexyl moiety, enhancements in both open‐circuit voltage (V_oc) and short‐circuit current (J_sc) are achieved for the quasi‐solid‐state DSSCs. The V_oc gains originating from the suppression of charge recombination were quantitatively investigated and are in good agreement with the experimentally observed V_oc enhancements. Therefore, an enhanced solar energy conversion efficiency (η) of 6.16 %, constituting an increase by 23 %, is achieved under standard AM 1.5 sunlight without the use of coadsorbant agents for the quasi‐solid‐state DSSC based on sensitizer FNE40 , which bears the branched alkyl group, in comparison with that based on FNE38 carrying the linear alkyl group. This work presents a design concept for considering the crucial importance of the branched alkyl substituent in novel metal‐free organic sensitizers.     

Dye‐Sensitized Solar Cells Based on a Donor–Acceptor System with a Pyridine Cation as an Electron‐Withdrawing Anchoring Group

New hemicyanine dyes ( CM101 , CM102 , CM103 , and CM104 ) in which tetrahydroquinoline derivatives are used as electron donors and N‐(carboxymethyl)‐pyridinium is used as an electron acceptor and anchoring group were designed and synthesized for dye‐sensitized solar cells (DSSCs). Compared with corresponding dyes that have cyanoacetic acid as the acceptor, N‐(carboxymethyl)‐pyridinium has a stronger electron‐withdrawing ability, which causes the absorption maximum of dyes to be redshifted. The photovoltaic performance of the DSSCs based on dyes CM101 – CM104 markedly depends on the molecular structures of the dyes in terms of the n‐hexyl chains and methoxyl. The device sensitized by dye CM104 achieved the best conversion efficiency of 7.0 % (J_sc=13.4 mA cm^?2, V_oc=704 mV, FF=74.8 %) under AM 1.5 irradiation (100 mW cm^?2). In contrast, the device sensitized by reference dye CMR104 with the same donor but the cyanoacetic acid as the acceptor gave an efficiency of 3.4 % (J_sc=6.2 mA cm^?2, V_oc=730 mV, FF=74.8 %). Under the same conditions, the cell fabricated with N719 sensitized porous TiO₂ exhibited an efficiency of 7.9 % (J_sc=15.4 mA cm^?2, V_oc=723 mV, FF=72.3 %). The dyes CM101 – CM104 show a broader spectral response compared with the reference dyes CMR101 – CMR104 and have high IPCE exceeding 90 % from 450 to 580 nm. Considering the reflection of sunlight, the photoelectric conversion efficiency could be almost 100 % during this region.     

BiVO4‐TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method

Composite photocatalyst films have been fabricated by depositing BiVO₄ upon TiO₂ via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP‐OES), XPS, photoluminescence and Mott–Schottky analyses. SILAR processing was found to deposit monoclinic‐scheelite BiVO₄ nanoparticles onto the surface, giving successive improvements in the films′ visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO₄ conduction band and valence band lying cathodically shifted from those of TiO₂. The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo‐first‐order rate constant of 0.004 min^?1. As a reference material, the same SILAR modification has been made to an inactive wide‐band‐gap ZrO₂ film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO₄–ZrO₂ system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self‐sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst′s conduction band.     

A Shifted Double‐Diamond Titania Scaffold

Photonic crystals are expected to be metamaterials because of their potential to control the propagation of light in the linear and nonlinear regimes. Biological single‐network, triply periodic constant mean curvature surface structures are considered excellent candidates owing to their large complete band gap. However, the chemical construction of these relevant structures is rare and developing new structures from thermodynamically stable double‐network self‐organizing systems is challenging. Herein, we reveal that the shifted double‐diamond titania scaffold can achieve a complete band gap. The largest (7.71 %) band gap is theoretically obtained by shifting 0.332 c with the dielectric contrast of titania (6.25). A titania scaffold with similar shifted double‐diamond structure was fabricated using a reverse core–shell microphase‐templating system with an amphiphilic diblock copolymer and a titania source in a mixture of tetrahydrofuran and water, which could result in a 2.05–3.78 % gap.