A new carbon nanotubes (CNTs)–poly acrylonitrile (PAN) composite electrolyte for solid state dye sensitized solar cells

A new carbon nanotube (CNTs)–poly acrylonitrile (PAN) composite electrolyte was prepared by the thermal polymerization of acrylonitrile (AN) with CNTs for solid-state dye sensitized solar cells (DSSCs). It was found that the uniform CNT–PAN composite was formed due to the thermal polymerization of AN on CNTs. The strong bonding between CNTs and PAN could be confirmed by the characterization of XPS and Raman spectroscopy, resulting in the lowering of crystallinity and the increasing the ionic conductivity of composite electrolytes. On comparison with bare CNTs and the other composite electrolytes, the formation of triiodide (I₃⁻) ions in CNT–PAN composite electrolytes was drastically increased which was expected from the high ionic conductivity of electrolyte via I₃⁻/I⁻ redox couple. DSSCs fabricated with CNT–PAN composite electrolytes achieved relatively high conversion efficiency of 3.9% with an open circuit voltage (V_OC) of 0.57 V, short circuit current density (J_SC) of 10.9 mA/cm² and fill factor of 63.6%, which attributed to supply the higher extent of I₃⁻ ions from CNT–PAN composite electrolyte during the charge transport process.     

Carbon nanotubes-polyethylene oxide composite electrolyte for solid-state dye-sensitized solar cells

Novel carbon nanotubes (CNTs)-polyethylene oxide (PEO) composite electrolyte for dye-sensitized solar cell (DSSC) was prepared and characterized for the first time. The strong bonding and interaction between CNTs and PEO in CNTs-PEO composites was observed by the characterization of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectra. The introduction of CNTs into PEO matrix significantly improved the electrolyte properties of DSSC such as roughness, amorphicity and ionic conductivity. The solid-state DSSC fabricated with the optimum composite electrolyte (added 1% CNTs in PEO matrix, 1%CNT-PEO) achieved maximum conversion efficiency of 3.5%, an open circuit voltage (V_OC) of 0.589 V, short circuit current density (J_SC) of 10.64 mA/cm² and fill factor (FF) of 56%. The highest IPCE in the DSSC fabricated with 1%CNT-PEO electrolyte is ascribed to the improved ionic conductivity of composite electrolytes and enhanced interfacial contact between electrode and electrolyte.     

Composite electrolyte of heteropolyacid (HPA) and polyethylene oxide (PEO) for solid-state dye-sensitized solar cell

A novel heteropolyacid (HPA) and polyethylene oxide (PEO) composite electrolyte was prepared and applied as the solid electrolyte for solid-state dye-sensitized solar cell. Advanced HPA-PEO composite electrolytes could be prepared by the optimized mixture solvent of chloroform and methanol (ChMe), which possessed the enhanced morphological properties, ionic conductivity and amorphicity. It is due to the presence of well-dispersed HPAs on the texture of PEO with the strong interaction between them. DSSCs fabricated with HPA-PEO/ChMe electrolyte showed significantly high photovoltaic (PV) performance with the overall conversion efficiency of 3.1%, open circuit voltage of 0.524 V and a short circuit current of 9.7 mA/cm². HPA in the composite electrolytes may act as an electron acceptor to prohibit the photo-reduction of I⁻, resulting in the advanced photocurrent density and stability without significant decline of the PV performance for 7 days.     

Dye-sensitized solar cells employing polymers

Dye-sensitized solar cells (DSSCs) are of interest due to their potential use as inexpensive and environmentally friendly photovoltaic (PV) devices with acceptable power conversion efficiency (PCE). Platinum (Pt) metal is, traditionally, the preferred material for the counter electrode (CE) component of DSSCs, however, further development of iodide/triiodide (I⁻/I₃⁻) based liquid-electrolyte DSSCs using Pt remains challenging due to the high cost of this scarce metal and its susceptibility to corrosion. Additional concerns include solvent leakage and low chemical stability resulting from volatile liquid electrolyte used in DSSCs. In order to counteract this issue, polymer electrolytes or hole-transporters with higher mobilities are employed as a replacement for liquid electrolytes. In this regard, polymers can serve as efficient CE materials by replacing the platinized electrode in liquid-electrolyte DSSCs, while also substituting for the liquid electrolytes as polymer electrolytes or hole-transporters in solid-state or quasi solid-state DSSCs. Considering the fragility and shape restrictions of glass substrates, polymer substrates may also be used to replace rigid glass substrates, providing more flexible DSSCs. Herein, applications of the polymers as cell components (CEs, polymer electrolytes or hole-transporter, and plastic substrates) in DSSCs are discussed, with special focus on the role that polymers play in DSSCs and widely accepted reports of PV performance. The current understanding of the factors and strategies involved in improving the performance of polymers in DSSCs are reviewed and analyzed. In addition, the benefits, challenges and potential utility of polymers for use in DSSCs are assessed.     

Solid-state dye-sensitized hierarchically structured ZnO solar cells

A novel solid-state hierarchically structured ZnO dye-sensitized solar cell (DSC) was assembled by using TiO₂ as filler in polyethylene oxide (PEO)/polyethylene glycol (PEG) electrolytes and ZnO nanocrystalline aggregates as photoanode film. Under optimized composite polyelectrolyte containing PEO/oligo-PEG/TiO₂/LiI/I₂ the photovoltaic performance of the solid-state ZnO DSCs was significantly better, with an overall conversion efficiency (η) of 1.8% under irradiation of 100 mW/cm², which was higher than those of the cells with PEO/TiO₂/LiI/I₂ (η = 1.1%) or PEO/oligo-PEG/LiI/I₂ electrolyte (η = 1.5%). Further, the hierarchically structured ZnO-based cell showed a higher η value of 2.0% under 60 mW/cm² radiation. The morphologies, ionic conductivity of three different composite electrolytes and their performance to the DSCs were also studied by FESEM, I–V data, IPCE and EIS.     

Novel cyclic sulfonium iodide containing siloxane high performance electrolyte for dye-sensitized solar cell

A new type of solid and gel state electrolytes based on siloxane cyclic sulfonium iodides was synthesized and used in dye-sensitized solar cells. The resulting electrolytes were characterized by ¹H NMR, TGA, diffusion coefficient, and ion conductivity. The thermo-oxidative stabilities of the prepared ionic species are lower than that of DMII because the bond strength of S⁺–C in thiophenium is lower than that of N⁺–C in imidazolium. Among the three SiCSIs based electrolytes, SiCSI3 showed a maximum photo-conversion efficiency of 7.3%. In addition, the performance of the DSSCs showed relatively reasonable compared with the imidazolium type DMII electrolyte.     

Chitosan‐based gel film electrolytes containing ionic liquid and lithium salt for energy storage applications

Fabrication, characterization, and a comparative study have been performed for chitosan‐based polymer electrolytes using two different dispersion media. Chitosan gel film (solid) electrolytes are fabricated using acetic acid or adipic acid as the dispersant for chitosan in combination with ionic liquid and lithium salt. This quaternary system of chitosan, acetic acid or adipic acid, 1‐butyl‐3‐methylimadazolium tetrafluoroborate (ionic liquid), and lithium chloride is formed as an electrolyte for potential secondary energy storage applications. The ionic conductivities, thermal, structural, and morphological properties for these electrolytes are compared. The ionic conductivities for chitosan/adipic acid (CHAD) and for chitosan/acetic acid (CHAC) systems are in the range of 3.71 × 10⁻⁴−4.6 × 10⁻³ and 1.3 × 10⁻⁴ −3.2 × 10⁻³ S cm⁻¹, respectively. The thermal stability of CHAD‐based electrolytes is determined to be higher than that of CHAC‐based electrolytes. Preliminary studies are performed to determine the electrochemical stability of these materials as solid film electrolytes for electrochemical supercapacitors. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42143.     

Ionic liquid/polymer composite electrolytes by in situ photopolymerization and their application in dye-sensitized solar cells

A new kind of quasi-solid state electrolytes for dye-sensitized solar cells (DSCs) has been prepared by in situ photopolymerization from the precursor 1,6-hexanediol diacrylate (HDDA) in 1-hexyl-3-methyl imidazolium iodide (HMII). The optimal ratio of polymer/ionic liquid is determined by the conductivities of the electrolytes. In order to further increase the miscibility between ionic liquid and the polymer, oligomer polyethylene glycol dimethyl ether (PEGDME) is introduced. By optimization of the amount of PEGDME in the electrolyte, the DSCs using this kind of solid-state electrolytes can present 6.5% of light-to-electricity conversion efficiency under 41 mW cm⁻². In the meantime, the influence of PEGDME additive is detailedly investigated by electrochemical impedance spectrum (EIS) and intensity modulated photovoltage spectroscopy (IMVS) techniques. Preliminary long-term stability test revealed that this in situ photopolymerized electrolyte exhibits good stability after 1000 h thermal test.     

Increase ionic conductivity of a Zn2+/F− synergy Na3Zr2Si2PO12 solid electrolyte for sodium metal batteries

Na₃Zr₂Si₂PO₁₂ (NZSP) solid-state electrolyte is considered one of the most promising solid-state electrolyte because of their excellent electrochemical and thermal stability. Even though, the low conductivity of NZSP solid-state electrolytes hinders practical application. Therefore, an anions/cations co-assisting strategy is proposed by introducing the Zn²⁺ and F⁻. The influence of adding different amounts of Zn²⁺ and F⁻ on the Na⁺ conductivity of NZSP was investigated computationally and experimentally. The Zn²⁺/F⁻ co-assisting (Na_3.3Zr_1.85Zn_0.15Si₂PO₁₂) solid-state electrolyte exhibits the ionic conductivity of 0.722 mS cm⁻¹ at 30 °C, and the activation energy of ∼0.237 eV. Its applicability in a solid-state battery is tested, and the assembled Na/Na₃V₂(PO₄)₃ (NVP) battery exhibits an outstanding electrochemical performance of 98.4% capacity retention after being cycled at 0.5 C. Moreover, DFT calculations also have been used to demonstrate the effect of doping on the crystal structure and space migration energy barrier. This research provides new ideas for improving the electrochemical properties of inorganic solid electrolytes.     

Amphiphilic poly(vinyl chloride)-g-poly(oxyethylene methacrylate) graft polymer electrolytes: Interactions, nanostructures and applications to dye-sensitized solar cells

An amphiphilic graft copolymer, i.e. poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM) comprised of a PVC backbone and POEM side chains was synthesized via atom transfer radical polymerization (ATRP) and complexed with a salt for dye-sensitized solar cell (DSSC) applications. The coordinative interactions and structural changes of polymer electrolytes were investigated using FT-IR spectroscopy, wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC). Small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) revealed that the d-spacing between PVC domains was significantly increased upon the introduction of metal salt, ionic liquid and oligomer, indicating their selective confinement in the hydrophilic POEM domains. The ion-conducting POEM domains were well interconnected, resulting in high ionic conductivity (∼10⁻⁴ S/cm at 25 °C) and energy conversion efficiency (∼5.0% at 100 mW/cm²) in the solid-state.     

Influence of ionic additives NaI/I2 on the properties of polymer gel electrolyte and performance of quasi-solid-state dye-sensitized solar cells

The ionic additives NaI/I₂ in polymer gel electrolyte not only provide cations, but also affect the liquid electrolyte absorbency of the poly(acrylic acid)-poly(ethylene glycol) hybrid, which results in the change of ionic conductivity of polymer gel electrolyte and the photovoltaic performance of quasi-solid-state dye-sensitized solar cell. With the optimized components of liquid electrolyte containing 0.5 M NaI, 0.05 M I₂, 0.4 M pyridine, 70 vol.% γ-butyrolactone and 30 vol.% N-methylpyrrolidone, a 4.74% power conversion efficiency of quasi-solid-state dye-sensitized solar cell was obtained under 100 mW cm⁻² (AM 1.5) irradiation.     

Synthesis and characterization of poly(1‐vinyl‐3‐propylimidazolium) iodide for quasi‐solid polymer electrolyte in dye‐sensitized solar cells

The synthesis conditions of ionic liquid 1‐vinyl‐3‐propylimidazolium iodide (ViPrIm⁺I⁻) and Poly(1‐vinyl‐3‐propylimidazolium) iodide [P(ViPrIm⁺I⁻)] were studied in this work. P(ViPrIm⁺I⁻) as a single‐ion conductor providing iodine was designed to develop a quasi‐solid polymer electrolyte based on PVDF/PEO film for dye‐sensitized solar cells (DSSCs). The samples were characterized respectively by high‐performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance imaging (NMRI), gel permeation chromatography (GPC), etc. The results showed that the single‐ion conducting quasi‐solid polymer electrolyte (SC‐QPE) exhibited high ionic conductivity of 1.86 × 10⁻³ S cm⁻¹ at room temperature measured by CHI660C Electrochemical Workstation. Moreover, solar cells assembled using the SC‐QPE yielded an open‐circuit voltage of 0.83V, short‐circuit current of 8.01 mA cm⁻² and the conversion efficiency of 2.42%. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Anisotropic films photopolymerized from aligned cross-linkable gemini ammonium liquid crystals for ion conduction

Cross-linkable gemini ionic liquid crystals are prepared by jacketing the diammonium moiety between two biphenyl benzoate mesogens. Anisotropic films are obtained by photopolymerization of the macroscopically aligned gemini ionic liquid crystals for ion conduction. Small angle X-ray scattering (SAXS) measurements indicate that the monolayer nanostructure is formed in the films and scanning electron microscope (SEM) observations reveal that the smectic layers are perpendicular to the film surface. Electrochemical impedance spectroscopy (EIS) characterization shows that the films exhibit strong anisotropy in ion conduction. The ion conduction across the film is enhanced while that within the plane of the film is impeded. The ionic conductivity in vertical direction of the film reaches up to 10⁻³ cm S⁻¹ at 180 °C and the measured anisotropy (ratio of the measured conductivities in vertical direction of the film versus in parallel to the film) is 100–350. The photopolymerization of the cross-linkable gemini ammonium liquid crystals offers excellent potential for the development of solid electrolytes for electrochemical devices. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47349.     

Synergistic effect of ionic liquid and organo-functional silane on the preparation of silica based hybrid ionogels as solid-state electrolyte for Li-ion batteries

Having excellent safety and potentially high energy density, solid-state electrolytes can be used in large-scale energy storage applications instead of flammable and volatile organic solvent-based electrolytes. Aerogels are notable candidates for solid-state electrolytes due to their low density, high porosity, high specific surface area, stable thermal behavior, and ultralow dielectric constant. In this work, Li-doped silica ionogels were synthesized by the two-step sol-gel method by using trifunctional organosilane Methyltrimethoxysilane (MTMS), as silica co-precursor along with conventional precursor TEOS. In addition, 1,3-Butylmethylimidazolium bis(trifluorosulfonyl)imide (BMIMTFSI) was selected as an ionic liquid to provide ion mobility throughout the solid skeleton. The synthesized hybrid ionogels were characterized by FTIR, SEM, BET, and TGA analyzes. It was observed that the specific surface areas of the obtained ionogels varied between 685 and 725 m²/g. To examine the effect of Li⁺ ion concentration on ion conductivity, electrolyte solutions have prepared in different concentrations (0.5 ~ 2 M). The Li⁺ ion conductivity of the ionogel prepared with 2 M of Li⁺ ion solution (M-IGE-2) was determined as 4.06 × 10⁻⁴ S/cm by Potentiostatic EIS measurement and it possessed 3.3V of electrochemical stability.     

Effect of oligomer on dye-sensitized solar cells employing polymer electrolytes

The effect of oligomer (M _n =400–500 g/mol) on dye-sensitized solar cells (DSSC) employing polymer electrolytes consisting of poly(epichlorohydrin-co-ethylene oxide) (Epichlomer), LiI, 1-methyl-3-propylimidazolium iodide (MPII) and I₂ is investigated. Five kinds of oligomer, poly(ethylene glycol) (PEG, M _n =400 and 1,000 g/mol), poly(ethylene glycol) dimethyl ether (PEGDME), poly(propylene glycol) (PPG) and poly(ethylene glycol) diglycidyl ether (PEGDGE), were introduced to elucidate the role of terminal groups and chain length. The coordinative interactions and structures of polymer electrolytes were characterized by FT-IR spectroscopy and X-ray diffraction (XRD). The improved interfacial contact between the electrolytes and the electrodes by the oligomer addition was confirmed using a field-emission scanning electron microscope (FE-SEM). The electrolytes exhibited ionic conductivities on the order of 10^?4 S/cm, but PEGDGE electrolyte showed much lower value (～10^?8 S/cm). As a result, the energy conversion efficiency of DSSC was significantly affected by the oligomer. For example, the DSSC employing PEGDME with methyl terminal groups exhibited 3.95% at 100 mW/cm², which is 200-fold higher than that employing PEGDGE.     

Lithium Thiophosphate Glasses and Glass–Ceramics as Solid Electrolytes: Processing,Microstructure, and Properties

Lithium solid electrolytes are of major interest for solid-state batteries and electrochemical capacitors (ECs). Currently, the material selection space of liquid electrolytes is dominated by lithium salts paired with organics. Improved safety, as well as the need for higher temperature and high voltage operation, opens up opportunities for glass and ceramic alternatives in these important solid-state energy storage technologies. Lithium thiophosphates in the family x Li₂S + (1−x) P₂S₅ (mol fraction) possess room temperature ionic conductivities greater than 10⁻³(Ω-cm)^-1 in crystallized x = 0.70 (almost the highest in inorganic solid-state electrolytes). Within this review article, we address recent progress made in this class of material. We consider the role of densification on the Li-ion conductivity, as well as our recent data on the effect of densification on the electrochemical properties of the system. We cover the processing techniques of mechanical milling and pressure-forming, discuss microstructure, bulk versus surface conduction, and device integration. The systematic improvement in ionic conductivity with increased density suggests that bulk conduction dominates surface conduction and demonstrates that dense, rather than porous, lithium thiophosphate solid electrolytes are important in the design of solid-state batteries and ECs.     

Synthesis and characterization of urea-containing imidazolium iodide electrolyte for dye-sensitized solar cells

Novel gel-type ionic salts based on aminopropyl imidazolium iodide (APII) functionalized with urea were synthesized and used as the electrolyte in dye-sensitized solar cells (DSSCs). The synthesized APIIs were in a viscous gel state. The electrolytes exhibited the characteristics of an intra- or inter-molecular hydrogen bonding interaction through their urea bonds. The two synthesized electrolytes that contained two urea groups and two imidazolium salts simultaneously (APII-HM2, APII-HP2) were highly viscous and showed relative thermal stability compared to a commercial ionic liquid (IL) of DMII (methylmethylimidazolium iodide; DMII). These new electrolytes were examined by ¹H NMR spectroscopy and their ionic conductivities and diffusion coefficients were measured. Among the six APIIs, the single urea-containing electrolyte (APII-HP1) exhibited a maximum solar photo-conversion efficiency of 7.31%, which was slightly higher than that of the reference (DMII, 6.59%).     

Dye-Sensitized Tandem Solar Cells with Extremely High Open-Circuit Voltage Using Co(II)/Co(III) Electrolyte

For achieving a high open-circuit voltage (V_oc) in dye-sensitized tandem solar cells, series-connected tandem solar cells were fabricated. In order to optimize series-connected tandem solar cell systems, the current density of the top and bottom cells should be well matched to be identical, and the V_oc of each of the cells should also be as high as possible. Furthermore, the top cell should be transparent and the bottom cell should have the longer-wavelength absorption, for utilizing only the light passing through the top cell. This leads to a high V_oc. In this study, we report dye-sensitized tandem solar cells having an extremely high V_oc using the Co(bpy)₃^2+/3+ (bpy=2,2′-bipyridine) redox couple. Dye-sensitized tandem solar cells employing JK303/HC-A1 with the Co(bpy)₃^2+/3+ redox couple as the top cell and N749/HC-A4 with the I⁻/I₃⁻ redox couple as the bottom cell were shown to have an extremely high V_oc of >1.66 V, the highest value for dye-sensitized tandem solar cells reported to date.     

Characteristics of a dye-sensitized solar cell based on an anode combining ZnO nanostructures with vertically aligned carbon nanotubes

Electrical conductivity and a high surface area in the anode are of primary importance for the enhancement of photoelectric conversion efficiency (η) in dye-sensitized solar cells (DSSCs). This study reports on the fabrication of a DSSC anode using ZnO nanostructures. These ZnO nanostructures are coated on vertically aligned carbon nanotubes (CNTs) on stainless steel substrates using thermal chemical vapor deposition. The resulting CNTs provided a good electric connection between the ZnO overlayer and the stainless steel substrate. The photoelectric characteristics of the DSSCs were optimized with the immersion of dye for 15 hrs. Compared to the η of ZnO nanostructures on randomly distributed CNTs, the η of ZnO nanostructures on vertically aligned CNTs increased approximately 4-fold. This result showed that the vertically aligned CNTs coated with ZnO nanostructures had improved the performance of DSSC.     

In situ thermal polymerization of an ionic liquid monomer for quasi‐solid‐state dye‐sensitized solar cells

In situ thermal polymerization of a model ionic liquid monomer and ionic liquids mixture to form gel electrolytes is developed for quasi‐solid‐state dye‐sensitized solar cells (Q‐DSSCs). The chemical structures and thermal property of the monomers and polymer are investigated in detail. The effect of iodine concentration on the conductivity and triiodide diffusion of the gel electrolytes is also investigated in detail. The conductivity and triiodide diffusion of the gel electrolytes increase with the increasing I₂ concentration, while excessive I₂ contents will decrease the electrical performances. Based on the in situ thermal polymeric gel electrolytes for Q‐DSSCs, highest power conversion efficiency of 5.01% has been obtained. The superior long‐term stability of fabricated DSSCs indicates that the cells based on in situ thermal polymeric gel electrolytes can overcome the drawbacks of the volatile liquid electrolyte. These results offer us a feasible method to explore new gel electrolytes for high‐performance Q‐DSSCs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42802.