Study of hydrogen production in light assisted microbial electrolysis cell operated with dye sensitized solar cell

Hydrogen production with light as an additional energy source in a microbial electrolysis cell (MEC) is described. A ruthenium-dye (N719) sensitized solar cell with an open circuit potential (V_oc) of 602 mV was connected to the MEC. Hydrogen production was carried out by irradiating the DSSC connected across the MEC with a light intensity of 40 mW/cm² and also with natural sunlight. The DSSC was stable during various batch experiments. The acetate conversion efficiency and the coulombic efficiency based on the average of first two batches were 30.5 ± 2.5% and 40 ± 2% respectively. The cathodic recovery efficiency ranged from 72% to 86% during repeated batch experiments with an average of 78 ± 2.5%.     

Preparation of 1-methyl-3-propylimidazolium acetate and its application in dye sensitized solar cells

In this paper, we reported the preparation of 1-methyl-3-propylimidazolium acetate (MPIAc), which proceeded via the metathesis of 1-methyl-3-propylimidazolium iodide (MPII) and lead acetate or potassium acetate. The apparent diffusion coefficients of triiodide and iodide in binary ionic liquids, MPIAc and MPII with various weight ratios, were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. It was found that the apparent diffusion coefficients of triiodide increased and those of iodide slightly increased with the weight ratio increase of MPIAc and MPII. The dye sensitized solar cells with the electrolyte, which was composed of 0.13 M I₂, 0.10 M LiI, 0.50 M 4-tert-butylpyrdine in the binary ionic liquid electrolyte of MPIAc (employing potassium acetate) and MPII (weight ratio 0.2), gave short circuit photocurrent density of 9.40 mA cm⁻², open circuit voltage of 0.62 V, and fill factor of 0.57, corresponding to the photoelectric conversion efficiency of 3.34% at the illumination (air mass 1.5, 100 mW cm⁻²).     

An efficient nanostructured ZnO for dye sensitized degradation of Reactive Red 120 dye under solar light

Nanostructured ZnO has been synthesized by thermal decomposition of zinc oxalate without using any additives or solvents and characterized by XRD, TGA, BET, FE-SEM and HR-TEM techniques. XRD analysis showed that the synthesized catalyst has a hexagonal wurtzite-type polycrystalline structure. HR-TEM analysis revealed the formation of ZnO nanostructures and the increase in size of ZnO nanoparticle from 40 to 100 nm during the formation. Nano-ZnO is found to be more efficient than commercial ZnO for mineralization of Reactive Red 120 under solar irradiation. Addition of oxone influences the photodegradation efficiency. The recyclability of ZnO nanocrystals is found to be higher than the commercial ZnO. The promoting effects of ZnO nanocatalyst for the sensitized degradation of colorants in aqueous phase have been investigated. Mineralization of RR 120 was confirmed by gas chromatography and COD values.     

Performance variation of carbon counter electrode based dye-sensitized solar cell

The effect of dark and room temperature aging on the performance of carbon counter electrode based dye-sensitized solar cell (DSSC) has been investigated. Using nano size carbon as a counter electrode material, DSSC with power conversion efficiency of 7.56% was fabricated. Storing the devices in the dark at room temperature enhanced both the open-circuit voltage (V_OC) and fill-factor (FF) but reduced the short-circuit current density (J_SC). After 60 days of aging, carbon counter electrode DSSC retains 84% of its initial day efficiency (η). The variation in the current–voltage parameters was explained on the basis of electrochemical impedance spectroscopic (EIS) analysis.     

Simple size-controlled fabrication of Zn2SnO4 nanostructures and study of their behavior in dye sensitized solar cells

Zn₂SnO₄ nanostructures were obtained via facile and rapid co-precipitation approach in presence of amines with different long chain as a novel basic and capping agents. The effect of different amines such as NH₃, ethylenediamine, triethylenetetramine, tetraethylenepentamine on the size of Zn₂SnO₄ nanostructures were investigated. The results demonstrated that applying the appropriate amount of organic amine could be effective in particle size control. The obtained nanostructure products were specified by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and ultraviolet–visible (UV–vis) spectroscopy. Dye sensitized solar cells (DSSC) were created by the constructed electrodes as working electrode and then were studied by current density–voltage (J–V) curve. It was found that incorporating of TiO₂ nanoparticles to optimized Zn₂SnO₄ nanostructures has significant role on the constructed DSSCs photovoltaic properties.     

Thermal thiocyanate ligand substitution kinetics of the solar cell dye N719 by acetonitrile, 3-methoxypropionitrile, and 4-tert-butylpyridine

The kinetics of the thiocyanate substitution of the solar cell sensitizer [Ru(Hdcbpy)₂(NCS)₂]²⁻, 2(n-C₄H₉)₄N⁺ (H₂dcbpy=L=2,2′-bipyridine-4,4′-dicarboxylic acid), known as N719, by acetonitrile, 3-methoxypropionitrile, and 4-tert-butylpyridine (4-TBP) have been determined in both homogenous solutions and colloidal mixtures of N719-dyed TiO₂ nanocrystalline particles. Thiocyanate ligand substitution by the solvents (S) acetonitrile or 3-methoxypropionitrile in homogeneous solutions occurs at elevated temperatures (80–110 °C) by means of a simple slow pseudo-first-order reaction leading to the formation of the product [RuL₂(NCS)(S)]⁺ with a half-life time t_1/2 2000 h of N719 at 80 °C. If tert-butylpyridine (0.5 M) is added, the end product instead becomes [RuL₂(NCS)(4-TBP)]⁺ with a t_1/2 1000 h. When N719 is bound to TiO₂ particles, the reactions with S and 4-TBP give the same products as occur in the homogenous solutions; however, the reactions are approximately 10 times faster. For the reaction of a colloidal mixture of N719-dyed TiO₂ particles in acetonitrile containing 0.5 M 4-TBP, a t_1/2(het) of 120 h was calculated at 85 °C. The N719-based DSSC cells with acetonitrile and 4-TBP as solvent and additive are therefore not expected to be able to pass a 1000-h thermal stress test in the dark at 85 °C due to thermal degradation of the N719 dye. Adding guanidine thiocyanate to the colloidal solutions, however, decreased the rate of [RuL₂(NCS)(4-TBP)]⁺ formation by a factor of 2–10; it thus may be used as an additive to prevent the thermal degradation of thiocyanate-based ruthenium complexes in DSSC solar cells.     

Donor-acceptor-functionalized polymers for efficient light harvesting in the dye solar cell

This work describes the properties of a series of dye solar cells that were sensitized with hyperbranched polymers carrying two different chromophoric units. One of the units was a carboxylated ruthenium complex, acting as sensitizer and energy acceptor, while the other was a fluorescent dye, acting as additional light absorber and energy donor. Within this series of polymers the ratio between donor and acceptor entities (z_DA) was varied between 0 and ∼9. The influence of z_DA on the cell's spectral properties was studied. Our key result is that current may be generated via the energy transfer from multiple energy donors to one acceptor unit within the dye solar cell.     

Fabrication of CdS quantum dot sensitized solar cells via a pressing route

CdS quantum dots have been self-assembled on the surface of dispersed nanocrystalline TiO₂ particles, and a light-harvesting electrode has been fabricated from the resulting sensitized P25 particles using the pressing route. The spectroscopic and photochemical properties of photosensitized nanocrystalline TiO₂ electrodes were studied. The results indicate that electrode preparation by the pressing route may lead to partial loss or damage of the CdS coating and creation of regions that are inaccessible to the redox electrolyte. Nevertheless, the pressing method using pre-coated powders shows promise as a low cost method for the preparation of photoelectrodes in sensitized-solar cells.     

Influence of oxygen and water related surface defects on the dye sensitized TiO2 solar cell

Oxygen- and water-related surface defects on porous TiO₂ (anatase) can be well controlled by the oxygen and water partial pressures and therefore such defects are of technological relevance for dye sensitized TiO₂ solar cells. We investigated the action of oxygen and water-related surface defects in situ by impedance spectroscopy, photoconductivity, photoluminescence, and optical transmission as well as by characterizing solar cells which were prepared under respective conditions. Oxygen loss from the TiO₂ surface leads to electrical doping by Ti³⁺/oxygen donor states. Such defects create recombination paths for injected electrons back into the electrolyte. Pre-treatment of porous TiO₂ by chemisorption of water increases the open circuit voltage of the solar cells without altering the short circuit current. Water-related surface defects decrease the saturation current of the diode, probably by raising the barrier height at the TiO₂/electrolyte interface.     

Preparation of carbon dots/TiO2 electrodes and their photoelectrochemical activities for water splitting

Carbon dots with various functional groups can be employed as the potential sensitizer. In this study, carbon dots are obtained by electrochemical ablation of graphite rods in alkaline electrolyte. The better preparation condition is the applied potential of 40 V and the ablation time of 5 h. TiO₂ nanotube arrays and TiO₂ nanoparticles photoelectrodes are sensitized by the as-prepared carbon dots through using impregnation method. Carbon dots/TiO₂ nanotube arrays electrodes exhibit greater photoelectrochemical hydrogen production activities than carbon dots/TiO₂ nanoparticles electrodes. It is because more carbon dots can be well combined with TiO₂ nanotube arrays. Based on the IPCE values in visible light region, the role of carbon dots on TiO₂ nanotube arrays electrode depends on the up-converted PL behaviors from their surface states and the alkaline electrolyte. The results provide insight into carbon dots that serve as sensitizer of TiO₂ photoelectrode in water splitting system of alkaline solution.     

Silicon solar cells with antireflection diamond-like carbon and silicon carbide films

Optical properties of diamond-like carbon and silicon carbide (SiC) films in dependence on deposition conditions were investigated. It was established that the films having refractive index from 1.6 to 2.3 may be obtained. The film optical bandgap and hardness may be changed from 1.5 to 4 eV and from 1 to 20 GPa, correspondingly. The films were deposited onto the front side of silicon solar cells (SCs). It has been shown that deposition of single- or two-layer diamond-like carbon antireflection (AR) coatings enables the SCs efficiency to be improved 1.35–1.5 times. The improvement is connected with decreasing of reflection losses and passivation of recombination active centers. SiC AR coatings improve the solar cell efficiency up to 1.3 times.     

Applications of carbon materials in photovoltaic solar cells

Carbon-based photovoltaic cells (PVCs) have attracted a great deal of interest for both scientific fundamentals and potential applications. In this paper, applications of various carbon materials in PVCs, especially in silicon-based solar cells, organic solar cells and dye-sensitized solar cells, are reviewed. The roles carbon materials played in the PVCs are discussed. Further research on solar cells comprised solely of carbon is prospected.     

Electrical and optical studies of flexible stainless steel mesh electrodes for dye sensitized solar cells

Stainless steel (SS) mesh was used to fabricate anodes for flexible dye sensitized solar cells (DSSC) in order to evaluate them as replacements for more expensive Transparent Conductor Oxides (TCO's). SS mesh performance was analyzed and it was determined that oxidation of SS during the sintering of titania particles affects the transport and interface resistance of the device. Thus a thin layer of non-porous titania coating was added onto the mesh to protect the electrode from oxidation. Comparing with Fluorine doped Tin Oxide (FTO), SS mesh was found to have higher interface resistance but the overall series resistance was lower due to higher conductivity of metals. The effects of SS mesh opening size and microstructure on the performance of the device was analyzed and design strategies to obtain high efficiency flexible SS mesh DSSC are provided.     

Environmental aspects of electricity generation from a nanocrystalline dye sensitized solar cell system

A Life Cycle Assessment, LCA, of a nanocrystalline dye sensitized solar cell (ncDSC) system has been performed, according to the ISO14040 standard. In brief, LCA is a tool to analyse the total environmental impact of a product or system from cradle to grave. Six different weighing methods were used to rank and select the significant environmental aspects to study further. The most significant environmental aspects according to the weighing methods are emission of sulphur dioxide and carbon dioxide. Carbon dioxide emission was selected as the environmental indicator depending on the growing attention on the global warming effect. In an environmental comparison of electricity generation from a ncDSC system and a natural gas/combined cycle power plant, the gas power plant would result in 450 g CO₂/kWh and the ncDSC system in between 19–47 g CO₂/kWh. The latter can be compared with 42 g CO₂/kWh, according to van Brummelen et al. “Life Cycle Assessment of Roof Integrated Solar Cell Systems, (Report: Department of Science, Technology and Society, Utrecht University, The Netherlands, 1994)” for another thin film solar cell system made of amorphous silicon. The most significant activity/component contributing to environmental impact over the life cycle of the ncDSC system is the process energy for producing the solar cell module. Secondly comes the components; glass substrate, frame and junction box. The main improvement from an environmental point of view of the current technology would be an increase in the conversion efficiency from solar radiation to electricity generation and still use low energy demanding production technologies. Also the amount of material in the solar cell system should be minimised and designed to maximise recycling.     

Integrating optimal amount of carbon dots in g-C3N4 for enhanced visible light photocatalytic H2 evolution

Carbon dots (CDs) hold great promise for photocatalytic application owning to their low production cost, unique optical properties, as well as excellent stability and conductivity. Integrating CDs in graphite carbon nitride (g-C₃N₄) nanosheets helps to broaden visible light absorption, retard charge recombination and promote photoelectrons transport. Herein, we demonstrated a simple strategy to introduce CDs on g-C₃N₄ nanosheets by hydrothermal treatment of ginkgo leaves followed by thermal polymerization of urea. We found that there was were two volcano-trends in the photocatalytic H₂ evolution rate with the increase of CDs loading. As a result, the optimized CDs/g-C₃N₄ nanocomposites demonstrated a superior hydrogen evolution rate as high as 3.12 mmol g^?1·h^?1 and 14.4% apparent quantum efficiency (AQE) was achieved at 420 nm visible light irradiation. The contribution of CDs towards the photocatalytic hydrogen evolution enhancement was discussed in depth via experiment characterization and Density functional theory (DFT) calculation. This work may shed light on the rational design and bottom-up synthesis of eco-friendly energy conversion materials with high-performance and low cost.     

Synthesis and characterization of boron-doped Si quantum dots for all-Si quantum dot tandem solar cells

Multiple layers of Si quantum dots (QDs) in SiO₂ with a narrow size distribution were synthesized by a co-sputtering technique. Structural, electrical and optical properties of Si QD/SiO₂ multilayer films with various boron (B) concentrations introduced during the sputtering process were studied. X-ray photoelectron spectroscopy (XPS) revealed B-B/B-Si bonding, which suggests possible boron inclusion in the nanocrystals. The addition of boron was observed to suppress Si crystallization, though the boron concentration was found to have little effect on the QD size. Reductions in film resistivity were observed with the increase in boron concentration, which is believed to be a consequence of an increase in carrier concentration. This is supported by a large decrease in the activation energy accompanying the drop in resistivity, consistent with the Fermi energy moving towards the valence bands. The photoluminescence (PL) intensity was found to decrease with increase in boron concentration.     

Synthesis and characterization of naphthyridine and acridinedione ligands coordinated ruthenium (II) complexes and their applications in dye-sensitized solar cells

Naphthyridine and acridinedione coordinated ruthenium (II) complexes were synthesized and characterized. Their applications in dye-sensitized solar cells were demonstrated. From the I–V curves, the short-circuit photocurrent (I_SC) and the open-circuit photovoltage (V_OC) were measured. A maximum current conversion efficiency (η) of about 7.7% was obtained for 5-amino-4-phenyl-2-(4-methylphenyl)-7-(pyrrolidin-1-yl)-1,6-naphthyridine-8-carbonitrile (pmpn) coordinated ruthenium (II) complex.     

Synthesis of TiO2 submicro-rings and their application in dye-sensitized solar cell

In this paper, novel TiO₂ submicro-rings were synthesized via potentiostatic anodization of titanium powder coated on transparent conducting oxide glass. The TiO₂ submicro-rings film was characterized by SEM, XPS and 3D optical profiling. Accordingly, a possible growth mechanism of submicro-rings was discussed. The TiO₂ submicro-rings based dye-sensitized solar cell (DSSC) with the film thickness of ca. 3.1 μm was assembled and a conversion efficiency of 1.36% was achieved under AM 1.5 illumination. The photoelectron transport properties of TiO₂ submicro-rings based DSSC were also discussed according to the electron impedance spectroscopy.     

The degradation of dye sensitized solar cell in the presence of water isotopes

The effects of water content on the degradation behavior of dye-sensitized solar cells were studied by adding water isotopes (H₂O, D₂O, and H₂¹⁸O) to the electrolytes. Time-dependent photovoltaic performance of the water-added DSSCs was monitored accompanied with the diffuse-reflectance infrared Fourier transform (DRIFT) technique and electrochemical impedance spectroscopy (EIS) measurement. DRIFT technique was utilized to study the chemical reactions that occurred on the working electrodes (TiO₂). EIS was implemented to evaluate the effects of the charge-transfer resistance at the interfaces between TiO₂/dye/electrolyte. Results show that the degradation rates of the cells in presence of water isotopes were in the order of H₂O>D₂O>H₂¹⁸O. In addition, the values of open-circuit voltage (V_oc) and fill factor (FF) for the water-added cells increased within first 12 h sun irradiation. However, their short-circuit current (J_sc) and efficiency (η) decreased during the sun irradiation. Moreover, a new peak assigned to LiNCS was noticed after soaking in water-added electrolytes for 48 h, attributing to the interaction of lithium ions with free thiocyanate ions from the dye.     

An improved preparation of 3-ethyl-1-methylimidazolium trifluoroacetate and its application in dye sensitized solar cells

In this paper, we reported an improved preparation of 3-ethyl-1-methylimidazolium trifluoroacetate (EMITA), which proceeded via efficient reaction of 1-methylimidazole and ethyl trifluoroacetate under solvent-free conditions using Teflon-lined, stainless steel autoclaves. It was shown that the procedure was simple and eco-friendly. The apparent diffusion coefficients of triiodide and iodide in binary ionic liquids, EMITA and 1-methyl-3-propylimidazolium iodide (MPII) with various weight ratios, were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. It was found that the apparent diffusion coefficients of triiodide slightly increased and those of iodide decreased with the weight ratio increase of EMITA and MPII. The dye sensitized solar cells with the electrolyte, which was composed of 0.13 M I₂, 0.10 M LiI, 0.50 M 4-tert-butylpyrdine in the binary ionic liquid electrolyte of EMITA and MPII (weight ratio 1:2), gave short circuit photocurrent density of 7.88 mA cm⁻², open circuit voltage of 0.61 V, and fill factor of 0.67, corresponding to the photoelectric conversion efficiency of 3.22% at the illumination (Air Mass 1.5, 100 mW cm⁻²).