An efficient method to prepare high-performance dye-sensitized photoelectrodes using ordered TiO<Subscript>2</Subscript> nanotube arrays and TiO<Subscript>2</Subscript> quantum dot blocking layers

High-performance dye-sensitized photoelectrodes using ordered TiO₂ nanotube arrays (TNTs) and TiO₂ quantum dot blocking layers are fabricated. The free-standing TNT membranes with perfect ordered morphology are prepared by three times of anodic oxidation on Ti foils. These TNT membranes can be easily transported to conductive glasses to fabricate front-side illuminated photoelectrodes. By changing anodic oxidation duration, the thickness of TNT membranes can be controlled, which shows significant influence on the UV-Vis reflectance and absorption abilities of TNT-based photoelectrodes and further influence photovoltaic performance of dye-sensitized solar cells (DSSCs). The highest power conversion efficiency (PCE) of DSSCs about 6.21 % can be obtained by using TNT membranes prepared with anodic oxidation of 3 h. For further improving photovoltaic performance of DSSCs, TiO₂ quantum dot (QDs) blocking layers are inserted between conductive glasses and TNT membranes in the photoelectrodes, which show remarkable effects. The highest PCE of DSSCs with this kind of blocking layers can increase to 8.43 %, producing 35.75 % enhancement compared with that of the counterparts without TiO₂ QD blocking layers.     

Pechini based titanium sol as a matrix in TiO<Subscript>2</Subscript> pastes for dye-sensitized solar cell application

The influence that the degree of polyesterification has on a titanium sol (Ti-sol) prepared via the Pechini method that acts as a matrix in TiO₂ pastes used for dye sensitized solar cells is reported. The different content of the polyester in the Ti-sol was realized by varying the heating time of the Ti-sol. Titanium dioxide pastes were prepared by introducing a commercial TiO₂ nanopowder into the Ti-sols. The TiO₂ layers were tested as photoanodes in dye-sensitized solar cells (DSSCs). The most appropriate degree of polyesterification was achieved by heating the Ti-sol for 0.5 and 1 h, while longer heating deteriorates the TiO₂ layer morphology. The highest efficiency of the DSSCs based on an ionic liquid electrolyte was 6.3% measured under standard test conditions (100 mW/cm², AM 1.5, 25 °C).     

Photovoltaic performance of dye-sensitized solar cells assembled by in-situ chemical cross-linking

Quasi-solid state dye-sensitized solar cells (DSSCs) were assembled by in-situ chemical cross-linking of a gel electrolyte precursor containing liquid electrolyte. The DSSCs assembled with this cross-linked gel polymer electrolyte showed higher open circuit voltage and lower short-circuit photocurrent density than those of DSSCs with liquid electrolyte. Addition of SiO₂ nanoparticles into the cross-linked gel polymer electrolyte significantly improved the photovoltaic performance and long-term stability of the DSSCs. The optimized quasi-solid state DSSC showed high conversion efficiency, 6.2% at 100 mW cm^?2 with good durability.     

Synthesis of organic sulfobetaine‐based polymer gel electrolyte for dye‐sensitized solar cell application

We have synthesized eco‐friendly, economic, and equally efficient polysulfobetaine‐based gel electrolyte to the alternative of liquid electrolyte in the fabrication of dye‐sensitized solar cells (DSSCs) for the first time. This nitrogen‐rich and highly conductive polysulfobetaine was synthesized by an easy and facile method without the use of any catalyst and explored for its DSSC application. The synthesized polymer gel electrolyte exhibited good ionic conductivity about 6.8 × 10^?3 Scm^?1 at ambient temperatures. DSSCs were fabricated based on this polysulfobetaine gel electrolyte and studied for their performance based on photovoltaic parameters. The DSSC photovoltaic results were appreciable and are Voc = 0.82 V, Jsc = 11.49 mA/cm², FF = 66%, and PCE = 6.26% at 1 sun intensity. These values are slightly lower than conventional liquid electrolyte‐based DSSC shown as Voc = 0.78 V, Jsc = 12.90 mA/cm², FF = 69%, and PCE = 7.07%, both at 100 mWcm^?2. Conductivity and photovoltaic parameters of the device reveals that as prepared polysulfobetaine‐based polymer gel electrolyte may be useful in the fabrication of DSSC and other electrochemical devices. Copyright © 2017 John Wiley & Sons, Ltd.     

N-doped TiO<Subscript>2</Subscript> applied in low-temperature-based dye-sensitized solar cells

With urea as nitrogen source, N-doped TiO₂ powders were synthesized and fabricated for low-temperature dye-sensitized solar cells (DSSCs) by the method of doctor-blade, and the highest temperature of the whole process was 120 °C. SEM, TEM, XRD, DRS, and XPS were used to analyze the microstructure of the N-doped TiO₂ powders. EIS, Bode plot, UV–Vis and I–V were employed to measure the photovoltaic performance of the DSSCs. The maximum photoelectric conversion efficiency (η) was 5.18 % when the amount of the doped nitrogen was 4 %, and, when compared with the η of 4.22 % for pure TiO₂, the short circuit current was increased by 22.2 % and the efficiency was increased by 22.7 %. It has been shown that the doped nitrogen could effectively suppress TiO₂ crystal phase transition from anatase to rutile, and decrease the size of particles. Therefore, the increased photoelectric conversion efficiency of the N-doped TiO₂-based DSSC was ascribed to the more suitable crystal phase, sizes and inner structure.     

Enhanced photovoltaic characterization and charge transport of TIO2 nanoparticles/nanotubes composite photoanode based on indigo carmine dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have established themselves as an alternative to conventional solar cells owing to their remarkably high power conversion efficiency, longtime stability and low-cost production. DSSCs composed of a dyed oxide semiconductor photoanode, a redox electrolyte and a counter electrode. In these devices, conversion efficiency is achieved by ultra-fast injection of an electron from a photo excited dye into the conduction band of metal oxide followed by subsequent dye regeneration and holes transportation to the counter electrode. The energy conversion efficiency of DSSC is to be dependent on the morphology and structure of the dye adsorbed metal oxide photoanode. Worldwide considerable efforts of DSSCs have been invested in morphology control of photoanode film, synthesis of stable optical sensitizers and improved ionic conductivity electrolytes. In the present investigation, a new composite nano structured photoanodes were prepared using TiO₂ nano tubes (TNTs) with TiO₂ nano particles (TNPs). TNPs were synthesized by sol–gel method and TNTs were prepared through an alkali hydrothermal transformation. Working photoanodes were prepared using five pastes of TNTs concentrations of 0, 10, 50, 90, and 100 % with TNPs. The DSSCs were fabricated using Indigo carmine dye as photo sensitizer and PMII (1-propyl-3-methylimmidazolium iodide) ionic liquid as electrolyte. The counter electrode was prepared using Copper sulfide. The structure and morphology of TNPs and TNTs were characterized by X-ray diffraction and electron microscopes (TEM and SEM). The photocurrent efficiency is measured using a solar simulator (100 mW/cm²). The prepared composite TNTs/TNPs photoanode could significantly improve the efficiency of dye-sensitized solar cells owing to its synergic effects, i.e. effective dye adsorption mainly originated from TiO₂ nanoparticles and rapid electron transport in one-dimensional TiO₂ nanotubes. The results of the present investigation suggested that the DSSC based on 10 % TNTs/TNPs showed better photovoltaic performance than cell made pure TiO₂ nanoparticles. The highest energy-conversion efficiency of 2.80 % is achieved by composite TNTs (10 %)/TNPs film, which is 68 % higher than that pure TNPs film and far larger than that formed by bare TNTs film (94 %). The charge transport and charge recombination behaviors of DSSCs were investigated by electrochemical impedance spectra and the results showed that composite TNTs/TNPs film-based cell possessed the lowest transfer resistances and the longest electron lifetime. Hence, it could be concluded that the composite TNTs/TNPs photoanodes facilitate the charge transport and enhancing the efficiencies of DSSCs.     

PVDF/PAN/SiO<Subscript>2</Subscript> polymer electrolyte membrane prepared by combination of phase inversion and chemical reaction method for lithium ion batteries

PVDF/PAN/SiO₂ polymer electrolyte membranes based on non-woven fabrics were prepared via introducing a chemical reaction into Loeb-Sourirajan (L-S) phase inversion process. It was found that physical properties (porosity, electrolyte uptake and ionic conductivity) and electrochemical properties were obviously improved. A favorable membrane structure with fully connective porous and uniform pore size distribution was obtained. The effects of PVDF/PAN weight ratio on the morphology, crystallinity, porosity, and electrochemical performances of membranes were studied. The optimized PVDF/PAN (70/30 w/w) (designated as M_pc30) polymer electrolyte membrane delivered excellent electrolyte uptake of 246.8 % and the highest ionic conductivity of 3.32 × 10^?3 S/cm with electrochemical stability up to 5.0 V (vs. Li/Li⁺). In terms of cell performance, the Li/M_pc30 polymer electrolyte/LiFePO₄ battery exhibited satisfactory electrochemical properties including high discharge capacity of 149 mAh/g at 0.2 C rate and good discharge performance at different current densities. The promising results reported here clearly indicated that PVDF/PAN/SiO₂ polymer electrolyte membranes prepared by the combination of phase inversion and chemical reaction method were promising enough to be applied in power lithium ion batteries.     

Effect of pore size/distribution in TiO2 films on agarose gel electrolyte-based dye-sensitized solar cells

This study develops a simple method to change the distribution of the pore size in a TiO₂ layer, using polyethylene glycol (PEG), while maintaining nearly the same surface area and porosity to clarify how large pores affect the performance of dye-sensitized solar cells (DSSCs). Specifically, a heating step at 100 °C for a specific duration is added prior to PEG removal and TiO₂ sintering at 400 °C. This process transforms the role of the PEG from a surfactant to a pore generator (porogen) and forms larger pores, depending on the loading and aggregation time for the PEG to gain larger pores. The effect of larger pores in TiO₂ films under 30 % PEG loading, on the performance of an agarose gel electrolyte-based DSSC, was further investigated using the ionic liquid, 1-allyl-3-ethylimidazolium iodide (AEII). The I–V characteristic and the electrochemical impedance spectroscopy analysis show that larger pores readily improve redox couple diffusion in a TiO₂ porous electrode and modify the interface between electrolyte and TiO₂. Using the optimized TiO₂ film with larger pores (30 % PEG loading, 100 °C/60 min), an efficiency of 7.43 % is achieved for the agarose gel electrolyte-based DSSC, which represents a 26.1 % improvement over TiO₂ without the addition of PEG.     

Synthesis and characterization of poly (1‐vinyl‐3‐butylimidazolium‐co‐methyl methacrylate) gel polymer electrolytes for dye‐sensitized solar cells: Effect of structure and composition

Herein, three ionic liquid random copolymers (P) containing 1‐vinyl‐3‐butylimidazolium bromide (VBImBr) and methyl methacrylate (MMA) with various molar ratios were prepared using conventional free radical polymerization. Afterward, their corresponding chemically cross‐linked copolymers (XP) were formed similarly in the presence of polyethylene glycol dimethacrylate (PEGDMA). The synthesized copolymers were characterized using FT‐IR, ¹H NMR, and GPC. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results showed that the rigidity and thermal stability of the copolymers depended on the ionic liquid content as well as the degree of cross‐linking. Gel polymer electrolytes were then prepared via obtained copolymers in the presence of a constant amount of synthesized imidazolium‐based ionic liquid. Among the copolymers, the P3 with in feed VBImBr:MMA molar ratio of 70:30 and the cross‐linked 1%‐XP3 copolymer prepared with 1 mol% of PEGDMA exhibited the highest conductivity and diffusion coefficients for I₃^¯ and I^¯. The power conversion efficiency of the optimized linear and cross‐linked copolymers (P3 and 1%‐XP3) under the simulated AM 1.5 solar spectrum irradiation at 100 mW cm^?2 were 3.49 and 4.13% in the fabricated dye‐sensitized solar cells (DSSCs), respectively. The superior long‐term stability and high performance of the gel electrolyte containing 1%‐XP3 suggested it as commercial gel electrolyte for future DSSCs.     

Photocatalytic degradation of trichloroethylene on platinum ion-doped TiO<Subscript>2</Subscript> under visible light irradiation

Porous platinum ion-doped TiO₂ (Pt–TiO₂) was prepared by a sol–gel method and demonstrated to have superior photocatalytic activity for the photodegradation of gaseous trichloroethylene (TCE) under visible light (VL) irradiation from a xenon lamp equipped with 422-nm cut-off filter. Kinetic studies were performed to clarify the effect of the doping amounts, space times, VL intensity, and mole fractions of TCE, O₂, and H₂O on the degradation of TCE. Under ultraviolet (UV) irradiation, the photocatalytic activity of Pt–TiO₂ was the same as that of TiO₂, indicating that the doped Pt ion did not act as a recombination center for the photogenerated holes and electrons. Based on the kinetic data and reaction products, we conclude that the photocatalytic degradation of TCE on Pt–TiO₂ under VL irradiation proceeds similarly to TiO₂ under UV irradiation. We also performed the photocatalytic degradation of TCE at the space time of 7.5 × 10⁷ g s mol^?1 in a tubular reactor packed with the Pt–TiO₂ pellets which are more suitable than the Pt–TiO₂ powder for the practical remediation of the contaminated gas. TCE was completely degraded, i.e. 100% conversion was achieved under VL irradiation but only a small quantity of CO₂ was formed with the stoichiometric ratio of [CO₂]_formed/[TCE]_degraded of ca. 0.33. By switching the gas stream containing TCE to humid air, more CO₂ was formed, indicating that the dichloroacetates accumulated on the Pt–TiO₂ surface are photodegradable to CO₂ under VL irradiation.     

Low-temperature versus oxygen plasma treatment of water-based TiO2 paste for dye-sensitized solar cells

High-temperature treatment steps in fabrication process of dye sensitized solar cell (DSSC) significantly contribute to the manufacturing costs and limit the use of temperature sensitive substrates. Therefore our aim was to develop a simple method for the preparation of water-based TiO₂ paste. The paste is based on peroxotitanic acid (PTA) sol–gel matrix and commercial TiO₂ nanoparticles (P25). Two fabrication processes to decompose/transform the PTA matrix in the printed TiO₂ layer are explored and combined: annealing at temperatures up to 250 °C and/or oxygen plasma treatment. The results show that the PTA matrix in the paste converts to anatase phase and to some extent also attaches to the TiO₂ nanoparticles P25 acting as an interconnecting network within TiO₂ layer. The transformation of the PTA matrix occurs around 250 °C, but in the presence of TiO₂ nanoparticles P25 it starts already at 120 °C. In addition the results reveal that the crystallization is achievable also solely with the oxygen plasma treatment. The efficiency of the TiO₂ layers, exposed to different post-deposition treatments, is evaluated in DSSCs. The results show that oxygen plasma treatment of the TiO₂ layers could efficiently replace temperature curing at 250 °C. Within this study the DSSCs with the efficiency up to 4.2 % measured under standard test conditions (1,000 W/m², AM1.5, 25 °C) were realized.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Correlation between the structural,electrical and electrochemical performance of layered Li(Ni<Subscript>0.33</Subscript>Co<Subscript>0.33</Subscript>Mn<Subscript>0.33</Subscript>)O<Subscript>2</Subscript> for lithium ion battery

The Li(Ni_0.33Co_0.33Mn_0.33)O₂ (LNCMO) cathode material is prepared by poly(vinyl pyrrolidone) (PVP)-assisted sol-gel/hydrothermal and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly (ethylene glycol) (Pluronic-P123)-assisted hydrothermal methods. The compound prepared by PVP-assisted hydrothermal method shows a comparatively higher electrical conductivity of ~2?×?10^?5 S cm^?1 and exhibits a discharge capacity of 152 mAh g^?1 in the voltage range of 2.5 to 4.4 V, for a C-rate of 0.2 C, whereas the compounds prepared by P123-assisted hydrothermal method and PVP-assisted sol-gel method show a total electrical conductivity in the order of 10^?6 S cm^?1 and result in poor electrochemical performance. The structural and electrical properties of LNCMO (active material) and its electrochemical performance are correlated. The difference in percentage of ionic and electronic conductivity contribution to the total electrical conductivity is compared by transference number studies. The cation disorder is found to be the limiting factor for the lithium ion diffusion as determined from ionic conductivity values.     

Sr,Zn co-doped TiO<Subscript>2</Subscript> xerogel film made of uniform spheres for high-performance dye-sensitized solar cells

This study comes up with the facile preparation of Sr,Zn co-doped TiO₂ xerogel film for boosting the short circuit current density of dye-sensitized solar cells (DSCs). The film contains 2.5-μm-diameter spheres assembled from 60 nm nanoparticles. X-ray photoelectron spectroscopy (XPS) shows that Sr²⁺ and Zn²⁺ ions to be well incorporated into the TiO₂ crystal lattice without forming specific strontium and zinc compositions. The crystallite size, phase composition, and band structure of the spheres depend on the dopants concentration. Isolated energy levels near valence band as a result of the foreign ions introduction improve the photocatalytic activity of the prepared TiO₂ spheres, enhancing the short circuit current density of the cells. The DSC co-doped with 0.075 at.% Sr and 0.4 at.% Zn showed the highest power conversion efficiency of 7.87 % and short circuit current density of 18.75 mA cm^?2 thanks to lower charge transfer resistance (2.16 Ω cm²), lower electron transit time (1.19 ms), and higher electron diffusion coefficient (18.1 × 10⁴ cm² S^?1) compared to the other cells, demonstrated by electrochemical impedance spectroscopy (EIS). The concept of the simultaneous introduction of alkaline earth ions and transition ions into TiO₂ xerogel films will open up a new insight into the fabrication of high performance DSCs.     

Nanocomposite solid polymeric electrolyte of 49% poly(methyl methacrylate)-grafted natural rubber–titanium dioxide–lithium tetrafluoroborate (MG49-TiO2-LiBF4)

A nanocomposite polymer electrolyte consisting of 49% poly(methyl methacrylate)-grafted natural rubber (MG49) as a polymer matrix, lithium tetrafluoroborate (LiBF₄) as a dopant salt, and titanium dioxide (TiO₂) as an inert ceramic filler was prepared by solution casting technique. The ceramic filler, TiO₂, was synthesized in situ by a sol–gel process. The ionic conductivity was investigated by alternating current impedance spectroscopy. X-ray diffraction (XRD) was used to determine the structure of the electrolyte, and its morphology was examined by scanning electron microscopy (SEM). The highest conductivity, 1.4 × 10⁻⁵ S cm⁻¹ was obtained at 30 wt.% of LiBF₄ salt addition with 6 wt.% of TiO₂ filler content. Ionic conductivity was found to increase with the increase of salt concentration. The optimum value of conductivity was found at 6 wt.% of TiO₂. The XRD analysis revealed that the crystalline phase of the polymer host slightly decreased with the addition of salt and filler. The SEM analysis showed that the smoother the surface of the electrolyte, the higher its conductivity.

     

Chitosan-modified TiO<Subscript>2</Subscript> as photocatalyst for ethanol reforming under visible light

This work reports the reforming of bio-ethanol on chitosan–TiO₂ hybrid photocatalysts at ambient temperature. The influence of chitosan composition on the photocatalytic performance of chitosan–TiO₂ hybrid was studied. The hybrids were characterized by CHN elemental analysis, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the preparation variables used for the incorporation of chitosan on TiO₂ promoted changes in the morphology, superficial area, crystal size and porosity of the photocatalyst, affecting the band gap of this semiconductor and consequently the reactivity of the chitosan–TiO₂ hybrids. The catalysts were evaluated for hydrogen production from ethanol under visible light. It was demonstrated that the calcination temperature of 623 K and a chitosan content of 20% were the most appropriate preparation conditions and the resulting product displays a pore size of 1.9 nm, crystal size of 11.3 nm, BET area of 178 m² g^?1 and band gap of 2.92 eV. The calcination temperature of 623 K and incorporation of 20% of chitosan obtained the same results in the conversion rate of hydrogen in comparison to the pure TiO₂ P25.     

Light expanded clay aggregate (LECA) as a support for TiO<Subscript>2</Subscript>, Fe/TiO<Subscript>2</Subscript>, and Cu/TiO<Subscript>2</Subscript> nanocrystalline photocatalysts: a comparative study on the structure,morphology, and activity

In this work, TiO₂ and doped TiO₂ photocatalysts (Fe/TiO₂ and Cu/TiO₂) were synthesized by the sol–gel method. The main objective of this study was to investigate the influence of dopants on the structure, morphology, and activity of the catalysts in powder and immobilized states. XRF, XRD, and SEM methods were used to characterize the catalysts. The structure and phase distribution of the nanocrystalline powders were identified by XRD. Nanoparticles crystallite size and the degree of crystallinity were affected by doping. The anatase contents of catalysts were achieved as follows: TiO₂ (5.89 %) < Fe/TiO₂ (42.17 %) < Cu/TiO₂ (70.28 %). It was indicated that the activity of the catalysts strongly depends on the anatase content. Under the same circumstances, copper-modified TiO₂ exhibited a twofold higher photocatalytic activity compared with TiO₂. The nanostructured catalysts were immobilized on light expanded clay aggregate (LECA) granules in order to investigate the effect of a novel support on the activity of the catalysts. Morphological changes are recognizable in the SEM images. Activity tests indicated that the best catalytic performance was assigned to Cu/TiO₂/LECA. After 120 min of irradiation, 61 % degradation of phenol in synthetic wastewater was achieved. The high photocatalytic activity of Cu/TiO₂/LECA confirms that LECA is as an excellent support.     

Effect of single-wall carbon nanotubes on the properties of polymeric gel electrolyte dye-sensitized solar cells

A hybrid of polymer/dispersed single-wall carbon nanotubes was utilized in networking a novel composition of gel electrolyte in dye-sensitized solar cells. The gel is composed of polyethylene glycol, polyvinyl pyrrolidone, single-wall carbon nanotubes, and I^?/I₃ ^? as electrolyte. Formation of the less conductive polyiodide species in electrolyte was prohibited by the addition of single-wall carbon nanotubes leading to the excellent photovoltaic behavior of the cell under simulated standard illumination of the fabricated device owing to the increased open circuit voltage (0.47 V). Electrochemical impedance spectroscopy was employed to quantify the charge transport resistance and the electron lifetime at the TiO₂ conduction band. Charge transport resistances at the TiO₂/dye/electrolyte interface were determined for the cells consisting of the non-gel reference and our new gel electrolytes, and it was indicated that the charge recombination between injected electrons and electron acceptors (I₃ ^?) in the redox electrolyte was remarkably retarded. Electrochemical parameters obtained by the fitting showed all of the resistances increased as compared to liquid electrolyte dye-sensitized solar cells that can be related to the increase in viscosity of the gel, which hinders the ionic transportation through the electrolyte. These results were also confirmed by the electron lifetime analyses. The characteristic peak shifted to a lower frequency in the Bode phase plot for the cell containing gel electrolyte which is an indication of a longer electron lifetime in comparison with that of the cell containing very conventional liquid electrolyte.     

Effects of water-based gel electrolyte on the charge recombination and performance of dye-sensitized solar cells

A new water-based solution of ion-conductive polymeric gel electrolyte composed of polyethylene glycol and polyvinylpyrrolidone as gel-forming substances, I^?/I₃ ^? as reversible redox couple, and various ratios of acetonitrile/water solvents was prepared and used in the fabrication of dye-sensitized solar cells. The effects of water on the electrochemical behavior of the prepared electrolyte solutions were examined by the cyclic voltammetry and electrochemical impedance spectroscopy techniques. Electrochemical impedance spectroscopy was employed to quantify the charge-transfer resistance and the electron lifetime at the TiO₂ conduction band. The characteristic peak shifted to a lower frequency in the Bode phase plot, which is an indication of a longer electron lifetime for the cell containing more water content. Photovoltaic performance of the cells prepared by the new water-based gel electrolyte was studied. Changes in the current density–voltage (J–V) characteristics can be explained based on the effect of water on the energetics and kinetics of charge transport and charge recombination in the dye-sensitized solar cells (DSSCs). It was observed that the increase in open-circuit voltage (V _oc) and fill factor and decrease in J _SC were noticeable for cells containing water-based gel electrolyte. It was indicated that the charge recombination between injected electrons and electron acceptors (polyiodide) in the redox electrolyte was remarkably inhibited by the increase of water. The photovoltaic performance stability of the DSSC containing gel electrolyte solution including 50 wt% of water was examined, and it was shown that it is more stable than conventional cells considerably for 168 h. Energy conversion efficiency of 2.30 % was achieved, under illumination with a simulated solar light of 100 mW cm^?2.     

Stability of CdS-coated TiO<Subscript>2</Subscript> solar cells

The obstacle to realize the large-scale production of dye-sensitized solar cells (DSSCs) is its long-term stability and reliability problem. One of the main causes of the instability of DSSCs is the use of liquid electrolytes. In addition, exploring nano-sized particles of CdS as an alternative sensitizer for organic dye in dye-sensitized solar cells have attracted great interest due to the high cost and the instability of the organic dye. Our study has found that the CdS-coated TiO₂ cell degrades rapidly in the liquid electrolytes even under dark environment. In this work, a solid-state solar cell structure of Glass/FTO/TiO₂/CdS:Cu/FTO/glass was successfully made with an efficiency of 0.7%. CdS:Cu served as both the p-type conductor and absorber. No efficiency was obtained for cell structures of glass/FTO/TiO₂/CdS/FTO/glass. This indicates the effectiveness of hole conducting behavior of CdS:Cu. This is the first time that this type of solid-state solar cell is reported and improved stability is demonstrated.