Incident Photon Conversion Efficiency Research Articles

A DFT Study of Solvent and Substituent Effects on the Adsorptive and Photovoltaic Properties of Some Selected Porphyrin Derivatives for DSSC Application.

A DFT/TD-DFT method was employed to study the effects of structural modification and solvent variation on the solubility, adsorptive, and photovoltaic properties of six porphyrins (A-F) obtained by structurally modifying two literature porphyrins A and D. The properties of interest were studied in vacuum, acetonitrile (AcCN), dichloromethane (DCM), dimethyl sulphoxide (DMSO), and ethanol (EtOH) for possible application of the molecules as sensitizers in dye-sensitized solar cells (DSSCs). Electronic absorption properties of the molecules were computed via potential energy surface scan, and thermodynamic data were obtained by DFT calculations in the selected media. Solubility properties of the molecules were mostly enhanced with DMSO as the solvent. The adsorptivity of the molecules onto mesoporous titanium (IV) oxide surface were predicted to be enhanced in the presence of DMSO. Most of the molecules were found to exhibit their highest photovoltaic activity measured in terms of the incidentphoton conversion efficiency (IPCE) in AcCN and DCM, rather than in DMSO due to its high viscosity and the ability to use its oxygen to form the catenating O-Ti4+ bond with the Ti4+ of the TiO2, causing inhibition of electron movement on the semiconductor surface. In general, the computed photovoltaic (PV) properties were found to be enhanced with -CO2H group as the substituent, and in AcCN or DCM as the solvent.

Photocatalytic activity of B-doped nano graphene oxide over hydrogenated NiO-loaded TiO2 nanotubes

A hydrogenated NiO-loaded anatase TiO2 with unique heterostructure nanotube arrays (denoted as H:(NiO/TiO2)) NTs were synthesized, followed by the attachment of boron-doped reduced nanographene oxide nanoparticles (B-nGO NPs) to form a vigorous composite photoelectrode B-nGO/H:(NiO/TiO2) NTs. The p-n junction created between p-type NiO and n-type TiO2 produces sufficient built-in electric field to facilitate the electron–hole pair separation and boost the interfacial electron transfer, subsequently a hydrogenation treatment to adjust the donor density and maximize the electron–hole separation. The microstructure characterization with synchrotron-based X-ray techniques straightened out that the created NiO oxygen vacancies can provide emptier d-orbitals to accept more photoexcited electrons. With the incorporation of B-nGO NPs, the partially replacement of C atoms of nGO by B atoms can form an electron–hole-rich configuration in the heterostructure to decrease the Fermi level, with a more rapid electron transfer toward TiO2 substrate during photocatalysis, which also confirmed by quantum-chemical calculations. The as-synthesized B-nGO/H:(NiO/TiO2) NTs exhibited a high photocurrent density (2.0 mA/cm2) and an effective photoconversion efficiency (2.07%) under simulated sunlight irradiation (AM1.5G, 100 mW/cm2). The eventuated photoconversion efficiency is 6 times enhanced with respect to the pristine TiO2, along with an impressive hydrogen evolution rate of 31 μmol/h/cm2. Moreover, the photocurrent durability test has confirmed the stability of B-nGO/H:(NiO/TiO2) electrode, with only a slight decay of <1% after continuous illumination for more than 4 h. Incident photon conversion efficiency spectra have revealed a boosted photo-response under visible light region (extended to ∼520 nm) with the synergistic attachment of NiO and B-nGO.

The influence of trinuclear complexes on light-induced hydrogen production

New trinuclear water reduction catalysts show turnover numbers for photochemical water splitting of up to 8899, a turnover frequency of 2737 h−1 and an incident photon conversion efficiency of 2.1%, thus outperforming mononuclear analogues.

A Theoretical Evaluation of the Efficiencies of Metal-Free 1,3,4-Oxadiazole Dye-Sensitized Solar Cells: Insights from Electron–Hole Separation Distance Analysis

Herein, some novel metal-free 1,3,4-oxadiazole compounds O1–O7 were evaluated for their photovoltaic properties using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations to determine if they can serve as metal-free organic dyes in the use of dye-sensitized solar cells (DSSCs). To understand the trends in the relative efficiencies of the investigated compounds as dyes in DSSCs, their electron contributions, hole contributions, and electron–hole overlaps for each respective atom and fragment within the molecule were analyzed with a particular focus on the electron densities on the anchoring segments. As transition density matrices (TDM) provide details about the departure of each electron from its corresponding hole during excitations, which results in charge transfer (CT), the charge separation distance (Δr) between the electron and its corresponding hole was studied, in addition to the degree of electron–hole overlap (Λ). The latter, single-point excitation energy of each electron, the percentage electron contribution to the anchoring segments of each compound, the incident-photon-conversion-efficiency (IPCE), charge recombination, light harvesting efficiency (LHE), electron injection (Φinj), and charge collection efficiency (ncollect) were then compared to Δr to determine whether the expected relationships hold. Moreover, parameters such as diffusion constant (Dπ) and electron lifetime (t), amongst others, were also used to describe electron excitation processes. Since IPCE is the key parameter in determining the efficiency, O3 was found to be the best dye due to its highest value.

Constructing two-dimensional heterojunction through decorating covalent organic framework with MoS2 for enhanced photoelectrochemical water oxidation

Photoelectrochemical (PEC) water splitting is regarded as one of the most effective route to address energy crisis and environmental issues. Two-dimensional covalent organic frameworks (2D COFs) have made some advances in PEC water splitting owing to their functionalized building blocks, remarkable structural stability, and unique conjugated structures, etc. Unfortunately, the PEC performance of COFs is severely hindered because of the poor surface charge transfer, surface recombination at the photoanode/electrolyte junction, and sluggish oxygen evolution reaction (OER) kinetics. Herein, we report an efficient 2D heterojunction through decorating a 2D COF with MoS2 for enhanced PEC water oxidation. The photocurrent density and incident photon conversion efficiency (IPCE) of the resultant photoanode are effectively improved by constructing 2D COF-based heterojunction. Such a strategy of constructing 2D heterojunction can not only efficiently accelerate the charge separation and transfer but also promote the separation of photogenerated electron-hole pairs for oxygen evolution. This work provides rational suggestions for developing COF-based photocatalysts to address the energy crisis and various environmental issues.

Tungsten Trioxide Photoanode-Palladium Cathode Cell for Solar Seawater Splitting

N-type semiconductor-tungsten trioxide (WO3) finds application in a large variety of fields including photocatalysis, gas sensors, smart windows or as a substrate for heterogeneous catalysts. This presentation will focus on recent improvements in optoelectronic and photoelectrochemical (PEC) properties of WO3 thin films achieved in our laboratory. The semitransparent WO3 films are formed on F-doped tin oxide (FTO) conductive glass substrates, using a sol-gel method, by depositing the precursor layer-by-layer and annealing sequentially in the flow of oxygen. Use of appropriate mixtures of tungstic acid and organic structure-directing agents that form the WO3 film precursor, combined with a two-step annealing, allows the formation of highly crystalline nanostructured (NS) electrodes with controlled, large porosity. This renders possible the permeation of the whole mesoporous film by the electrolyte. Annealing of the as-deposited samples in oxygen above 500°C ensures structural ordering with formation of monoclinic WO3. Since none among photostable (metallic oxide) semiconductors exhibits band-edge energy levels that match those of hydrogen and oxygen evolution reactions to allow unassisted water splitting, the present efforts focus on minimizing the bias voltage required to perform visible light-driven photooxidation of water. In fact, a bias voltage of the order of 1 V may be provided by several single-junction PV cells likely to operate in a tandem device with the PEC cell. Despite visible-light absorption range of the WO3 films restricted to 500 nm, under standard conditions, i.e. at 1.23 V vs RHE and under simulated AM 1.5G solar light (100 mW/cm2), stable anodic water splitting photocurrents exceeding 4.5 mA/cm2 are regularly attained.This presentation will principally focus on photoelectrolysis experiments employing synthetic seawater electrolyte, in a two compartment (separated by a sintered glass diaphragm) cell, that showed dominant (with 60-70% Faradaic efficiency) formation of chlorine at the WO3 photoanode with remarkably stable photocurrents reaching 4.7 mA/cm2. In fact, as demonstrated in an earlier work from our laboratory1, the WO3 photoelectrodes exhibit preferentially oxidation of anions (including Cl-) of the acidic aqueous electrolytes. However, in contrast with the Cl- ions, the photooxidation of oxy-anions of acidic electrolytes leads generally to the "passivation" of the WO3 electrodes due to the formation of the surface layers of peroxo species.1 The only identified exception is the methane-sulfonic acid that allows oxygen generation at the WO3 photoanode with large stable photocurrents.2 In the case of seawater photoelectrolysis, the operating potential point at which the photocurrent approaches saturation occurs at ca 0.4 V below E(Cl-/Cl2)=1.36 V vs SHE. Consistently, the incident photon conversion efficiencies (IPCEs) reach a maximum of 85% over 390-410 nm range of wavelengths.3 Good mechanical and chemical stability of the WO3 electrodes in the presence of chlorine evolved from seawater was confirmed by monitoring the photocurrents over a 20 hours-long continuous photoelectrolysis runs.A schematic diagram of the seawater splitting PEC cell, including a NS WO3 film photoanode and a Pd sheet cathode, used in our experiments is shown below.Fig. 1 Schematic diagram of the seawater splitting PEC cell.The current of CO2 gas passing through the seawater represents a possible option for maintaining slightly acidic pH in the cathodic cell compartment. The important advantage of the adopted PEC cell configuration is to circumvent the problem of gas separation, i.e. chlorine/oxygen formed at the photoanode and hydrogen generated at the Pd cathode that is stored in the form of a Pd-H hydride. The storage of hydrogen generated in a PEC water splitting device in the form of a hydride, opens the possibility of its subsequent use as an anode in a hydride-oxygen battery.Such sunlight-driven PEC seawater splitting device can be implemented in remote places to provide on-site relatively small amounts of chlorine for disinfecting purposes including purification of drinking water.More generally, the prospect of using seawater electrolyte for a larger scale PEC hydrogen generation would release the strain on vital fresh water resources. Considering relatively low concentration of Cl- ions in seawater, roughly equivalent to 0.5 M NaCl, the photoelectrolysis delivering photocurrents in the range of mA/cm2 appears well suited for such applications.

NickelPalladium alloy–reduced graphene oxide as counter electrode for dye-sensitized solar cells

In this work, nickel-palladium (NiPd) alloy-reduced graphene oxide (rGO) has been prepared via liquid-phase deposition (LPD) technique and applied as counter electrode (CE) of dye-sensitized solar cell (DSSC). The effect of Ni content on the properties of the sample and the performance of the device utilizing the CE has been investigated. The morphology of the sample is described by rumples and white strips distributed on the ITO surface. The device utilizing the CE prepared with the Ni:Pd ratio of 20:1 owns the highest power conversion efficiency (η) of 2.13%. This is due to this device possesses the lowest series resistance (Rs) of 84.6 Ω and the highest incident photon conversion efficiency (IPCE) of 11.30%. The findings of this work reveal that NiPd-rGO has potential to substitute platinum (Pt) as CE of DSSC since its η is comparable to that of Pt based device.

A DFT/TD-DFT study on the possible replacement of Ru(II) with Fe(II) in phthalocyanine-based dye-sensitized solar cells

Density functional theory and time-dependent density functional theory (DFT/TD-DFT) methods have been used to study the photo-voltaic and photophysicochemical properties of some metal-free and metal-containing phthalocyanine (Pc) derivatives (1–12) for application in dye-sensitized solar cells (DSSCs). The TD-DFT and molecular ground-state data were used to estimate the relative position of the TiO2 conduction band edge to the lowest unoccupied molecular orbital (LUMO) position (δp). The diffusion coefficients (Dπ), and oscillator strengths (f) at maximum absorption wavelengths of the molecules in the visible or near-infrared (near-IR) region were also estimated. Fluorescence emission (ϕf) and charge collection (ηc) efficiencies obtained using the method reported recently by our group were used in estimating the dyes’ incident photon conversion efficiency (IPCE). The estimated parameters have been used to characterize the dyes and evaluate their suitability for application in photo-voltaic technology both in gas phase and in acetonitrile. The overall results showed that iron(II) could be a possible substitute for ruthenium ion, as the choice metal ion for phthalocyanine-based DSSCs.

Unexpected high efficient dye sensitized solar cell based NiWO4 decorated bio activated carbon nanosheets hybrid photoanodes by one-pot facile hydrothermal approach

A facile route has been highlighted for the fast synthesis of tube-like, 1-dimensional (1-D) nickel tungstate (NiWO4) nano-assemblies decorated on the bio carbon (BC) nanosheets by one step hydrothermal technique. Monoclinic crystalline structure with nanotubes was identified through X-ray diffraction (XRD), Scanning electron microscope (SEM) and Transmission electron microscope (TEM) analysis. The nanotubes were uniformly wrapped on the BC nanosheets, which results in high surface area (113 m2/g) and porous nature (8.5 nm). The significant reduction in the band gap energy (2.69–2.36 eV) and prevent the recombination of electron-hole pair was further explored by the UV–Vis diffuse reflectance (DRS) and Photoluminescence (PL) results. The chemical composition and valance state of the samples were further analyzed by compositional analysis is done with inductively coupled plasma atomic emission spectroscopy (ICP-AES), Energy dispersive spectra and X-ray photoelectron spectra (XPS) analysis. The sandwich type dye sensitized solar cell (DSSC) was fabricated and study the J-V characteristics studies. The results reveal that NiWO4 modified BC hybrid photoanode show high photo-conversion efficiency (12.5%) and incident photon-conversion efficiency (83%) than compared with other photoanode materials (BC, and NiWO4). NiWO4/BC material also demonstrated strongly stability during long time in the PCE%. The improved photovoltaic mechanism of the hybrid materials under solar light was also discussed.

The effects of W/Mo-co-doped BiVO4 photoanodes for improving photoelectrochemical water splitting performance

The poor electrical conductivity of bismuth vanadate (BVO) can be improved by metal-doping at optimum percentage. Previously, we improved the photoelectrochemical (PEC) properties of BVO photoanodes by optimizing the different atomic percentage of molybdenum (Mo). Here, we co-doped BVO simultaneously with tungsten/molybdenum (W/Mo) to enhance the water splitting properties of BVO photoanodes. At optimum co-doping percentages of 0.5 %W-2%Mo BiVO4 (0.5W-2Mo-BVO) the photocurrent density maximum was ∼ 0.97 mA cm−2 at 0.6 V vs. Ag/AgCl. The water splitting was performed under 100 mW. cm-2 irradiation and 0.6 V vs. Ag/AgCl applied voltage for 0.5W-2Mo-BVO. The H2 production was 19.5 μmol.cm-2 after 2 h at optimized W/Mo co-doping. W/Mo co-doping into BiVO4 greatly improved the electron mobility, as demonstrated by photocurrent, Mott-Schottky, electrochemical impedance, open circuit potential (ΔOCP) and incident photon conversion efficiencies (IPCE) measurements. As compared to pure BVO, 0.5W-2Mo-BVO showed ∼2700-fold increase in the donor concentration (ND) and greatly decreased (1/60) space charge layer thickness (WSCL), which induced efficient charge carrier mobility and enhanced the PEC performance.

Characteristics of dye-sensitized solar cells (DSSCs) using liquid and gel polymer electrolytes with tetrapropylammonium salt

In this work, liquid electrolytes (LEs) and gel polymer electrolytes (GPEs) containing tetrapropylammonium iodide (TPAI) salt, propylene carbonate, ethylene carbonate, N,N-dimethylformamide and (I−/I3−) redox couple have been prepared. For GPEs, the additional material was poly(ethylene oxide). The impedance of these electrolytes was measured using electrochemical impedance spectroscopy to determine their ionic conductivity. Conductivity was found to increase with salt content in LEs whereas in GPEs, conductivity was initially enhanced but it was followed by decrement. The highest ionic conductivity for the GPE and LE were 2.53 mS cm−1 (0.20 g TPAI) and 8.98 mS cm−1 (0.25 g TPAI), respectively at room temperature. Dye-sensitized solar cells (DSSCs) were fabricated using all LEs and the highest conducting GPE. At 100 mW cm−2 illumination, DSSC with LE exhibited the efficiency of 6.61% with short circuit current density, Jsc= 18.69 mA cm−2, open circuit voltage, Voc = 0.68 V and fill factor, FF = 0.52 whereas DSSC using GPE delivered the efficiency of 3.29% with Jsc= 11.78 mA cm−2, Voc = 0.65 V, FF = 0.43. The highest incident photon conversion efficiency (IPCE) at 520 nm is 45.5% for DSSC with 0.25 g TPAI LE and 41.1% for DSSC with GPE at the same wavelength.

Synthesis and characterization of novel tetra anchoring A2-D-D-D-A2 architecture sensitizers for efficient dye-sensitized solar cells

Novel metal free organic dyes coded TET(RA)4, TET(CA)4, and TET(QA)4 were designed, synthesized, and characterized as effective sensitizers for dye sensitized solar cells (DSSCs). These new push-pull sensitizers used a strong electron donor consisting of 3,4-ethylenedioxythiophene and two triphenylamine molecules connected together to form a TPA-EDOT-TPA (TET) motif, which is directly connected to tetra anchoring groups (A) without any π-spacers to construct A2-D-D-D-A2 architecture, three different anchoring series, viz. rhodanine-3-acetic acid (RA), cyanoacetic acid (CA), and 2-methyl quinoline-6-carboxylic acid (QA) were employed to investigate the influence of anchoring moieties on the electrochemical, thermodynamic, kinetics, and photovoltaic efficiency of DSSCs. The DSSCs devices showed a maximum overall power conversion efficiency (PCE) = 5.13%, short-circuit current density (JSC) = 12.71 mA.cm−2, open circuit voltage (VOC) = 0.62 V, and fill factor (FF) = 65.36% with a maximum incident photon conversion efficiency (IPCE) = 75% for TET(QA)4. The optical and electrochemical studies showed that TET(QC)4 achieved higher electron injection free energy (ΔG°inj) into CB edge of TiO2 as well as high recombination resistance (Rrec) compared to TET(RA)4, and TET(CA)4, which explains the outstanding charge separation and superior power conversion efficiency (PCE) of TET(QC)4 possessing quinoline-6-carboxylic acid (QC) anchoring group. Molecular modeling calculations using DFT and TD-DFT showed effective charge separation, where HOMO is delocalized over the donor scaffold (TPA-EDOT-TPA), and the LUMO is delocalized over only two anchoring groups on the same side of the donor system, which provides strong HOMO-LUMO overlap as well as intimate electronic coupling with TiO2 nanoparticle surface for electron injection. Further, the calculated values of the energy gaps (E0-0) and ground/excited stated oxidation potentials were in perfect agreement with the experimental results.

Dependence of the characteristics of dye-sensitized solar cells on amount tetrapropylammonium iodide

In this work, several liquid electrolytes (LE) have been prepared. The electrolytes contain tetrapropylammonium iodide (TPAI) salt with different salt content, propylene carbonate (PC), ethylene carbonate (EC), polyethylene oxide (PEO), dimethylformamide (DMF) and (I-/I3-) redox couple LE was used in the Dye-Sensitized Solar Cell (DSSC). DSSCs were fabricated and current density-voltage (J-V) characteristics measured. The highest incident photon conversion efficiency (IPCE) at 520 nm is 45.5% for DSSC with 0.25 g TPAI LE. At AM 1.5, DSSC with LE exhibits efficiency of 6.61% with Jsc= 18.69 mA cm-2, Voc= 0.68V and fill factor (FF) = 0.52.

Decoration of plasmonic Cu nanoparticles on WO3/Bi2S3 QDs heterojunction for enhanced photoelectrochemical water splitting

We report a WO3/Cu/Bi2S3 wherein incorporation of Cu nanoparticles (Cu NPs) to enhance the photoelectrochemical activity over WO3/Bi2S3. Cu NPs effectively harvest the light energy upon plasmon excitation and transfer the energy to contacted WO3, thereby improving the photoelectrochemical (PEC) performance. The WO3/Cu/Bi2S3 composite was characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD) to analyze the morphology and interfacial contact between the semiconductors. The photocurrent density and Solar-to-Hydrogen conversion efficiency for this composite is 10.6 mA cm−2 at 1.23 V (versus RHE) and 3.21% at 0.81 V (versus RHE), which are much higher than WO3/Bi2S3 with 4.02 mA cm−2 at 1.23 V (versus RHE) and 2.46% at 0.81 V (versus RHE) respectively. Moreover, the stability and photo-response of WO3/Cu/Bi2S3 were carried out through chronoamperometric studies. The composite retained its stability over 50 cycles without decay in PEC performance. High incident photon conversion efficiency (IPCE) value of about 51% is achieved which is evident from the high photocurrent density. Incorporation of Cu NPs increase the photoactivity which is evident from the photocurrent value. The increased activity of Cu NPs sandwiched composite is attributed for the quick electron transfer to semiconductor due to surface plasmon resonance (SPR) effect.

An approximate procedure for profiling dye molecules with potentials as sensitizers in solar cell application: A DFT/TD-DFT approach

Abstract A DFT/TD-DFT method was employed to study the photovoltaic properties of some metal-free and metal-containing organic compounds (A–G) for dye sensitized solar cells (DSSCs) application. Fluorescence emission ( ϕ f ) and charge collection ( η c ) efficiencies were obtained by deductive logic, and were used to determine the dyes’ incident photon conversion efficiency (IPCE). These parameters were used to evaluate the dye’s suitability for photovoltaic technology. The new approach could be a simple method of predicting dyes’ photovoltaic activities while avoiding the laborious experimental trial and error procedures, although it cannot be used to predict the actual efficiency of a DSSC.

Photo-deposition of cobalt-phosphate group modified hematite for efficient water splitting

In this work, Cobalt Phosphate Group (Co−Pi) Modified nanostructured hematite (α-Fe2O3) photoanodes films were deposited on fluorine-doped tin oxide (FTO) coated glass by means of the hydrothermal process. The α-Fe2O3 film morphology can be tuned from nanoparticle – based patterns to high-density cabbage-like structures as Co−Pi deposition time is increased.Systematic studies were performed to clarify the mechanisms that enhance water-splitting performance of α-Fe2O3 electrodes as Co−Pi deposition time increases. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Co-Pi/α-Fe2O3 photoanode exhibited higher photoelectrochemical activity than the α-Fe2O3 films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 30 s Co-Pi/α-Fe2O3 photoanode. All samples reached their best IPCE at 400 nm. IPCE values for 30 s Co-Pi hematite films were 5 times higher than that of α-Fe2O3 sample. For the α-Fe2O3 photoanode, the H2 evolution rate was ∼5.14 μmol cm−2 h−1. After decoration by Co-Pi, the rate increases to ∼7.31 μmol cm−2 h−1, showing an enhancement of about ∼ 42.2%. It was found that under illumination, the Co−Pi catalyst can efficiently collect and store photogenerated holes from the α-Fe2O3 electrode. This charge separation reduces surface state recombination, leading to the enhancement of the efficiency of water oxidation. Thicker catalytic Co−Pi films were found to increase charge separation and surface area, which in turn increase water oxidation efficiency. These results provide important new understanding of the catalytic enhancement and limitations of the Co−Pi catalyst once coupled to semiconductor electrodes for water-splitting applications.

Efficient Photocatalytic Fuel Cell via Simultaneous Visible-Photoelectrocatalytic Degradation and Electricity Generation on a Porous Coral-like WO3/W Photoelectrode.

Photocatalytic fuel cells (PFCs) have proven to be effective for generating electricity and degrading pollutants with a goal to resolve environmental and energy problems. However, the degradation of persistent organic pollutants (POPs), such as perfluorooctanoic acid (PFOA), remains challenging. In the present work, a porous coral-like WO3/W (PCW) photoelectrode with a well-designed energy band structure was used for the photoelectrocatalytic degradation of POPs and the simultaneous generation of electricity. The as-constructed bionic porous coral-like nanostructure greatly improved the light-harvesting capacity of the PCW photoelectrode. A maximum photocurrent density (0.31 mA/cm2) under visible light (λ > 420 nm) irradiation and a high incident photon conversion efficiency (IPCE) value (5.72% at 420 nm) were achieved. Because of the unique porous coral-like structure, the suitable energy band position, and the strong oxidation ability, this PCW photoelectrode-based PFC system exhibited a strong ability for simultaneous photoelectrocatalytic degradation of PFOA and electricity generation under visible-light irradiation, with a power output of 0.0013 mV/cm2 using PFOA as the fuel. This work provides a promising way to construct a reliable PFC using highly toxic POPs to generate electricity.

Charge generation performance enhancement by size-dependent Cu2GeSe3quantum dot-sensitized solar cells

Cu2GeSe3 quantum dot is introduced to instead of non-toxic CuInSe2 as a sensitizer for solar cells, which is employed to enhance the photovoltaic performance. Cu2GeSe3 quantum dots with various sizes are prepared by thermolysis process, which are employed for the fabrication of quantum dot-sensitized solar cells (QDSSC) according to assembly linking process. The optical absorption properties of the Cu2GeSe3 quantum dot-sensitized photo-electrodes have been obviously enhanced by the size optimization of quantum dots, which are better than that of CuInSe2-based photo-electrodes. Due to the balance on the deposition quantity and charge transfer property of the quantum dots, 3.9[Formula: see text]nm-sized Cu2GeSe3 QDSSC exhibits the highest current density value and incident photon conversion efficiency response, which result in a higher photovoltaic conversion efficiency than that of CuInSe2 QDSSC. The modulation of Cu2GeSe3 QDs will further improve the performance of photovoltaic devices.

Effect of pH on photocatalytic and photoelectrochemical (PEC) properties of monoclinic bismuth vanadate

Monoclinic bismuth vanadate (c-BVO) was prepared via simple calcination of solvothermally processed tetrahedral BiVO4. The physicochemical and morphological properties of c-BVO demonstrated the successful synthesis of the photoactive monoclinic phase from the tetrahedral phase, which has low photoactivity properties. The photoactivities of c-BVO were investigated using the photodegradation of methylene blue (MB) and photoelectrochemical (PEC) measurements in acidic (pH = 2.5), neutral (pH = 6.5) and basic (pH = 9.5) media. The photocatalytic activity of c-BVO was increased with increasing pH, achieved 99% MB degradation in the basic condition, compared with 70 and 45% in the neutral and acidic media, respectively. Although the tetrahedral BiVO4 showed mainly adsorption with negligible photodegradation, c-BVO demonstrated both good adsorption and photodegradation activities. The PEC results indicated that the photocurrent density was affected by both pH and applied voltage. Impedance measurements showed faster charge transfer in the neutral condition than in the acidic and basic electrolytes. The incident photon conversion efficiency (IPCE) showed very low activity for tetrahedral BiVO4, but in comparison it was enhanced by 20- and 10-fold for c-BVO in the visible and simulated solar light, respectively.

Ultrathin-layer α-Fe2O3 deposited under hematite for solar water splitting

This work proposes a new strategy to prepare a hematite (α-Fe2O3) bilayer photoanode by hydrothermally depositing α-Fe2O3 (B) on the α-Fe2O3 (A) films prepared by electrochemical deposition. Compact smooth surfaced α-Fe2O3 (A) films were electrochemically deposited on FTO (SnO2:F) substrates from an aqueous bath. The α-Fe2O3 (A), α-Fe2O3 (B), and α-Fe2O3/α-Fe2O3 bilayer films’ characteristics were defined by X-ray diffraction (XRD) measurements, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Pure crystalline α-Fe2O3 (B) films with a typical anisotropic-like nanoparticle formation, which exhibited nanostructured rods covering the substrate and formed the characteristic mesoporous film morphology, were hydrothermally deposited on α-Fe2O3 (A) films prepared by electrochemical depositing in a solution bath at 25 °C and a potential of − 0.15 V. The photocurrent measurements exhibited increased intrinsic surface states (or defects) at the α-Fe2O3 (A)/α-Fe2O3 (B) interface. The photoelectrochemical performance of the α-Fe2O3 (A)/α-Fe2O3 (B) structure was examined by chronoamperometry, which found that the α-Fe2O3 (A)/α-Fe2O3 (B) structure exhibited greater photoelectrochemical activity than the α-Fe2O3 (A) and α-Fe2O3 (B) thin films. The highest photocurrent density was obtained for the bilayer α-Fe2O3 (A)/α-Fe2O3 (B) films in 1 M NaOH electrolyte. This great photoactivity was ascribed to the highly active surface area, and to the externally applied bias that favored the transfer and separation of photogenerated charge carriers in α-Fe2O3 (A)/α-Fe2O3 (B). The improved photocurrent density was attributed to an appropriate band edge alignment of semiconductors and to enhanced light absorption by both semiconductors. The best performing samples were α-Fe2O3 (A)/α-Fe2O3 (B), which reached the maximum incident photon conversion efficiencies (IPCE) of 400 nm at the potential of 0.1 V. In this case, the IPCE values were 3-fold higher than those of the α-Fe2O3 (A) and α-Fe2O3 (B) films.