A study of reverse bias in a dye sensitised photoelectrochemical device

A dye-sensitized nanocrystalline solar subjected to reverse bias of 800 mV showed no measurable loss in performance. However, at 2000 mV, a dramatic and irreversible reduction in the cells performance is observed. Raman spectroscopy experiments suggested that no desorption of the photosensitising dye occurred. Spectroelectrochemical experiments revealed that an irreversible loss of intensity in the metal to ligand charge transfer band at 540 nm occurred. In practical terms, these results indicate that cells which are incorrectly connected to an array of cells or a system failure where potentials greater than 1500 mV are present, may be irreversibly damaged.     

Remarkable stability of the enhanced sharp photocurrent in methylviolet–C18 and rhodamine–C18 dye-sensitized photoelectrochemical cell with p-CuSCN

A remarkable stability in the sharp photo-current peak at 570 nm was found when p-CuSCN semiconductor photocathode was sensitized with double-dye LB films of rhodamine-C₁₈ (R-C₁₈) monolayers and methylviolet-C₁₈ (M-C₁₈) monolayers. At first, M-C₁₈ four monolayers were deposited on p-CuSCN and then, R-C₁₈ four monolayers were deposited on M-C₁₈ monolayers to make an molecular arrangement on the semiconductor (LB-(R-C₁₈(4)/M-C₁₈(4))/p-CuSCN). Such a photo-cathode exhibited a remarkable stability of steady-state photo-current in (10⁻² M) KI+(10⁻⁴ M) I₂ aqueous solution of pH=6.5, where the quantum efficiency reached was 45%, as estimated by correcting the dye absorption in the sharp photo-current peak at 570 nm. When four monolayers of M-C₁₈ and four monolayers of R-C₁₈ were separated with an arachidic acid LB films, sharp photo-current peak and its stability gradually decreased. This remarkable stability may be due to an efficient energy transfer process and an efficient charge separation caused by a strong interaction between the parallel electron-vibration planes of both M-C₁₈ and R-C₁₈ molecules.     

Optimisation of zinc oxide nanorods for use in dye sensitised solar cells

Abstract

Zinc oxide nanorods were fabricated via a low temperature hydrothermal method on fluorine doped tin oxide (FTO) substrates. The concentrations of hexamethylenetetramine (HMT) and polyethyleneimine (PEI) were optimised to give nanorods with an aspect ratio of ～110. Post-growth thermal annealing and nitrogen plasma treatment led to significant enhancement of the UV emission peak (380 nm) and suppression of the deep level emission peak (600 nm). Although the post-growth treatments did not appear to affect the crystallinity of the ZnO nanorods, the efficiency of dye sensitised solar cells constructed following the post-growth thermal treatments saw a decrease in efficiency.     

Size effects of WO3 nanocrystals for photooxidation of water in particulate suspension and photoelectrochemical film systems

Monoclinic WO₃ nanocrystals were synthesized by a hydrothermal reaction and post calcination. Their particle sizes were varied from 30 nm to 500 nm by changing calcination temperature from 500 °C to 800 °C. Photooxidation of water was studied in particulate suspension (PS) system and photoelectrochemical (PEC) film system. For PS system, WO₃ nanocrystals were suspended in 50 mM AgNO₃ solution to measure O₂ evolution rate. For PEC system, WO₃ films were fabricated by doctor blade method using synthesized nanocrystals. Photocurrent density was measured at AM 1.5 G (1 sun) solar condition in 0.5 M H₂SO₄. In PS system, the sample calcined at the highest temperature generated the largest amount of oxygen, whereas in PEC system the sample calcined at 600 °C showed the maximum photocurrent. The two systems also showed opposite response to deposition of the Pt co-catalyst. These different behaviors were attributed to different mechanisms of charge separation in the two systems.     

A photoelectrochemical solar cell based on ZnO/dye/polypyrrole film electrode as photoanode

Nanostructured ZnO film electrodes were prepared. A preliminary PEC solar cell based on nanostructured Zno/dye/polypyrrole (PPy) film electrode was fabricated. A fill factor of 0.754 and a high overall light to electricity conversion efficiency of 1.3% for this PEC solar cell were obtained. The sensitization mechanisms of the nanostructured ZnO electrodes were also discussed.     

Colloidal synthesis of CuInS2 nanoparticles: Crystal phase design and thin film fabrication for photoelectrochemical solar cells

This study reports the colloidal synthesis of copper indium disulfide (CuInS₂) nanoparticles in different crystal phases to be employed as thin film photoanodes in photoelectrochemical water splitting process. First, CuInS₂ nanoparticles with chalcopyrite-, zincblende-, wurtzite-as well as polytypic-phases have been synthesized using hot injection method. The effects of solvent, temperature and type of precursors on the phase design have been thoroughly investigated via various spectroscopic techniques such as XRD, SEM, HRTEM, UV-Vis and PL spectroscopy and Zeta particle size analysis. The XRD spectra have been revealed that the all the targeted nanoparticles had good crystallinity and free from undesired binary sulfides. The synthesized nanoparticles have been re-dispersed in N, N-dimethylformamide (DMF) to form nanoink paste and applied on fluorine doped tin oxide coated glass substrate by doctor blade technique. DMF has been found to be an enviable solvent for thin film fabrication since it could lead to the crack free and uniform surface formation. The chalcopyrite thin film has shown the best photoelectrochemical performance with the photocurrent density of ∼15 mA cm⁻² and conversion efficiency of 6.7%. Howbeit, thin films photoanodes bearing wurtzite, zincblende and polytypic CuInS₂ nanoparticles have been investigated to compare the performance of different crystal phases for photoelectrochemical solar cell applications. Moreover, it should be emphasized that all thin film electrodes have been investigated under 1-sun condition without any surface modification, chemical treatment and etching. Additionally, the thin films except wurtzite structure exhibited good stability along 2 h under dark and illuminated conditions.     

Optimization hydrogen production over visible light-driven titania-supported bimetallic photocatalyst from water photosplitting in tandem photoelectrochemical cell

Solar hydrogen production was investigated over a Cu-Ni doped TiO₂ photocatalyst from water photosplitting in a tandem photoelectrochemical cell, which was made up by connecting a modified photoelectrochemical cell to dye solar cell in a series. A mathematical representation for preparation parameters for hydrogen production was successfully generated. Optimization of hydrogen production was conducted with varying preparation parameters of Cu-Ni doped TiO₂ photocatalyst including molar ratios of water, acetic acid and Cu to titanium tetraisopropoxide. The optimum preparation parameters of photocatalyst was obtained at molar ratios of water, acetic acid and Cu to titanium tetraisopropoxide of 32, 4.9, and 5.9, respectively. Physical and photoelectrochemical characterization revealed that low content of water and Cu decreased the charge transfer resistance and charge carrier recombination rate on Cu-Ni/TiO₂ surface. This is attributed to the better crystallinity and less degree of agglomeration which led to obtain optimum particle size at this condition. Maximum hydrogen production rate of 2.12 mL/cm². h was achieved under the optimum condition using the tandem photoelectrochemical cell in the aqueous KOH and glycerol solution under visible light irradiation (λ > 400 nm).     

Dye-sensitized solar cell based on nanocrystalline ZnO thin film electrodes combined with a novel light absorbing dye Coomassie Brilliant Blue in acetonitrile solution

In this work, characterization of dye-sensitized solar cells (DSSC) using nanocrystalline ZnO thin film electrodes combined with a novel light absorbing dye Coomassie Brilliant Blue (CBB), in acetonitrile solution is reported. The absorption spectrum of this dye in acetonitrile solution indicates appreciable absorption in the range of 500–700 nm with a sharp peak at 597 nm indicating its possible use as a photosensitizer for ZnO. The current–voltage and efficiency characteristics of a DSSC based on this dye and ZnO acceptor are measured for two methods of depositing the ZnO. Better response is achieved for nanocrystalline ZnO thin films than for sprayed films in terms of cell output.     

Effect of film thickness and morphology on the performance of photoelectrochemical cells based on poly(terthiophene)

Photoelectrochemical cells have been fabricated from electrochemically deposited polyterthiophene films. The thickness of the photoactive layer was systematically varied by altering the charge density of the electrodeposited film. The morphology, optical absorption and photovoltaic performance of these devices have been characterised as a function of film thickness in order to gain a better understanding of the structure–function relationships in photoelectrochemical cells. Two distinct growth modes are observed. Initially a compact two-dimensional ‘precursor’ polymer film is formed up to a critical thickness of several hundred nanometres whereupon the growth of a ‘bulk’ three-dimensional film structure occurs. The photovoltaic efficiency of these cells appears to be governed by the ‘precursor’ film, which is characterised by a dense, uniform morphology of polymer of increasing conjugation length. On the other hand, the ‘bulk’ overlayer, which manifests as a nodular and highly cracked surface layer, appears to be primarily responsible for limiting device efficiency.     

Flexographic printing of graphene nanoplatelet ink to replace platinum as counter electrode catalyst in flexible dye sensitised solar cell

Abstract

A semitransparent catalytically active graphene nanoplatelet (GNP) ink was developed suitable for roll to roll printing onto a flexible indium tin oxide substrate at a speed of 0·4 m s^?1. Dye sensitised solar cells using this ink as a catalyst demonstrated efficiencies of 2·0%, compared with 2·6% for sputtered platinum. Given further optimisation, GNP inks have the potential to replace chemically reduced or sputtered platinum. This would have the benefit of replacing the chemical reduction or sputtering operations as well as providing potential material cost benefits.     

Fabrication of n-Cu2O electrodes with higher energy conversion efficiency in a photoelectrochemical cell

We observed an n-type photoresponse in cuprous oxide films, which were prepared by a simple method of immersing copper plates in a HCl solution of 3 pH at 40°C temperature, when they were used in a PEC cell. This photoresponse was much higher than the previously published values for n-Cu₂O electrodes which were prepared by other methods. The photocurrent obtained was in the order of 0.3 mA/cm² when the cell was illuminated with light intensity of 50 mW/cm². (The semiconductor electrode was biased to get a zero dark current.) The power conversion efficiency of the cell was 0.01%. The maximum quantum efficiency obtained was 15%. It is hoped that these values could be improved with a better understanding of the photoelectrochemical properties of the cell.     

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%.     

Investigation of plasticized UV-curable glycidyl methacrylate based solid polymer electrolyte for photoelectrochemical cell (PEC) application

A free standing electrolyte film containing poly glycidyl methacrylate (PGMA) as polymer host, lithium perchlorate (LiClO₄) as charge carrier and ethylene carbonate (EC) as plasticizer were successfully prepared with solution casting technique. Nuclear magnetic resonance spectroscopy (NMR) was used to investigate the chemical structure of the polymer. The analyses of polymer electrolytes were performed by impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and fourier transform infrared spectroscopy (ATR-FTIR). The solid polymer electrolyte exhibited the highest conductivity at room temperature and 373 K with the values of 3.4 × 10⁻⁴ S cm⁻¹ and 1.2 × 10⁻³ S cm⁻¹ at 80 wt.% of EC, respectively, in the presence of 80 wt.% of EC. FTIR spectroscopy analysis confirmed the interaction between lithium salt and oxygen atoms in polymer host in the presence of EC. Moreover, the electrolytes containing EC showed good electrochemical stability (−1500 to 3000) mV which reveals the potential of this polymer electrolyte for photoelectrochemical cell (PEC) application.     

Conductivity controlling of Cu2O film photoelectrode for water splitting by a novel electrochemical approach - Differential potentiostatic deposition

Cuprous oxide (Cu₂O) is a kind of low-cost and promising material for water splitting to produce hydrogen (p-type Cu₂O) and oxygen (n-type Cu₂O). However, the reason of conductivity transforming from p-type to n-type for Cu₂O films during potentiostatic deposition is waiting to be revealed. In this work, a novel electrochemical technology, differential potentiostatic deposition (DPD), is developed by coupling a 3-electrode setup with a resistor connected in series with the counter electrode circuit through a potentiostat. By this approach, deposition current density is adjusted in a short period to simulate different stages in a traditional potentiostatic deposition (TPD). The result shows that semiconducting conductivity of Cu₂O film changes from p-type to n-type with time during a long-term TPD in basic CuSO₄ solution. Employing the DPD method, conductivity of Cu₂O film transforms from p-type to n-type with current density decreasing. Through characterizing thickness, composition and photoelectrochemical performance of Cu₂O films, the mechanism of semiconducting conductivity transformation for Cu₂O films is proposed. Besides, the results indicate that the DPD is an effective method to tune the conductivity of metal oxide photoelectrodes for water splitting.     

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.     

Dye-sensitized solar cell with the hole collector p-CuSCN deposited from a solution in n-propyl sulphide

A method is devised for the deposition of CuSCN on ruthenium bipyridyl dye coated nanocrystalline TiO₂ films from a solution in n-propyl sulphide. The dye-sensitized solid state photovoltaic cell formed was found to yield higher short-circuit photocurrent, open-circuit voltage and efficiency compared to the cells made with CuSCN by other deposition techniques. Factors affecting the stability of the cell are investigated.     

A theoretical simulation of light scattering of nanocrystalline films in photoelectrochemical solar cells

A Monte Carlo simulation method of light scattering in nanocrystalline films based on solutions of Maxwell's equations is proposed. A nanocrystalline film is assumed to be superposition of randomly distributed nanoparticles and deviation of the nanocrystalline film from the randomness. Since a scattering field of the randomly and densely distributed nanoparticles can be neglected, a scattering field of the nanocrystalline film results in a sum of scattering fields of the deviant parts in the nanocrystalline film. In the method, configurations of the deviant parts are simulated with a random function of a computer language. A simulation converges in small number of the configuration patterns. The simulation theoretically demonstrates that almost all of the incident light to the nanocrystalline films in the photoelectrochemical solar cells penetrate without scattering.     

Enhanced hydrogen production over incorporated Cu and Ni into titania photocatalyst in glycerol-based photoelectrochemical cell: Effect of total metal loading and calcination temperature

The solar driven hydrogen production was successfully investigated in a glycerol-based photoelectrochemical cell (PEC) over nanostructured TiO₂ supported bimetallic Cu and Ni by adjusting total metal loading (5, 10, and 15 mol%) and calcination temperature (400, 450, 500, and 600 °C). The effects of the mentioned parameters on physicochemical and photoelectrochemical properties of prepared Cu–Ni/TiO₂ photoanodes were explored by using different characterization techniques. The hydrogen evolution was experimentally found to be affected total metal loading and calcination temperature. The calcined photocatalyst with the total metal loading of 5 mol% at 450 °C was identified as the most efficient photocatalyst by producing maximum accumulative hydrogen of 694.84 μmol. A high performance of this photocatalyst is mainly attributed to its proper particle size and great ratio of Ti³⁺:Ti⁴⁺ and Cu⁺:Cu²⁺ in TiO₂ matrix. These better physicochemical properties enhanced charge carrier separation, which retarded the charge recombination and enhanced the transportation of photo-induced electrons at the photoelectrode/electrolyte interface. The intermediates from photooxidation of glycerol were verified using high performance liquid chromatography, indicating a partial oxidation of glycerol with selective pathway in KOH (1 M) solution. This work demonstrates that optimization Cu–Ni/TiO₂ photoanode has the practical potential in PEC cell to generate hydrogen from solar and biomass energy.     

Synthesis and characterization of bifunctional β-MnO2-based Pt/C photoelectrochemical cell for hydrogen production

A manganese dioxide (β-MnO₂) photocatalyst for light-induced water splitting and hydrogen generation is studied via the impregnation and heat treatment method. The phase and fluorescence characterizations are examined by X-ray diffraction (XRD) and photoluminescence. A series of peaks for its (110) and (200) planes are identified as those for pure β-MnO₂ crystals with lattice spacings of 3.11 and 2.19 Å, respectively. The photoluminescence shows that the primary signals are located in the blue-violet spectral region, corresponding to the band-edge emission of β-MnO₂ (376 nm). Furthermore, two types of photoelectrochemical cell with added Pt are constructed to compare hydrogen production rates. A significant enhancement of light-induced hydrogen generation by water splitting is observed on Pt/β-MnO₂/C, with a hydrogen generation rate of 194.67 μmol cm⁻¹ h⁻¹, greater than that on a Pt/TiO₂/C photocatalyst, which can be attributed to the effective inhibiting of CO poisoning, thus maintaining the catalyst's surface area in methanol oxidation.