Electrolytes For Dye-sensitized Solar Cells Research Articles

Multi-component eutectic salts to enhance the conductivity of solvent-free ionic liquid electrolytes for dye-sensitized solar cells

Ionic liquids (ILs) possess intrinsic nonvolatility, low flammability, high ionic conductivity, high thermal and chemical stability, rendering themselves as excellent candidates for next generation dye-sensitized solar cells (DSSCs). Further improving the ionic conductivity of ionic liquid electrolytes is critical to the performance enhancement of DSSCs. Here, multi-component eutectic salts by mixing four ILs are proposed to achieve higher ionic conductivity compared to the individual one. In addition, the effect of mixing strategy on the eutectic salts was systematically investigated by diverse structural, thermal, electrochemical and photovoltaic characterization in detailed. It revealed that mixing strategy could not only tune the solid-state property of individual ILs to liquid-state eutectic salts, but also greatly improve the ionic conductivity of final multi-component eutectic salts. Thus, based on the multi-component eutectic salt, a power conversion efficiency (PCE) of 4.81% could be obtained by the resultant device. Moreover, the DSSCs with multi-component eutectic salt also display better stability than the referenced device with volatile organic solvent. The mixing eutectic salts offer us a feasible strategy to design high ionic conductive electrolytes for high performance dye-sensitized solar cells.

Size effects of imidazolium cations bearing cyanoethyl group on performance of dye-sensitized solar cells

Imidazoliums are commonly used ionic liquid cations in electrolyte in dye-sensitized solar cells (DSSCs). Here, the size effects of imidazolium cations bearing the cyanoethyl group on DSSC performance have been systematically investigated by introducing the different alkyl chains (C1–C12), by which size control is allowed in a range of 9–20 Å. The large cations slow down electron recombination and ion diffusion, but, unexpectedly, they suppress downward shift of TiO2 conduction band significantly affecting on electron injection process. While all the cations used in this work demonstrate a better power conversion efficiency than that for the common imidazolium analogue, the interplay among the key processes results in the best performance with the medium-sized cation C4 (11 Å). This work paves a way for design of efficient electrolyte cations for photovoltaic devices.

Preparation of Electrolytic Quasi-Solid-State Nanofibers for Dye-Sensitized Solar Cells

Nanofibers were prepared from a poly(acrylonitrile-co-vinyl acetate) [P(AN-co-VAC)]/polyvinylidene fluoride (PVDF) blend and used as a quasi-solid (QS) electrolyte for dye-sensitized solar cells (DSSCs). The effects of preparation parameters such as the flow rate and the weight percentage of PVDF on the fiber diameter, crystallinity, and ionic conductivity were investigated. Fourier-transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM) were used to characterize the prepared blend nanofibers. Current–voltage and electrochemical impedance spectroscopy (EIS) measurements were carried out on the fabricated DSSCs. It was found that the optimum weight ratio of P(AN-co-VAC) to PVDF in N,N-dimethylformamide (DMF) to produce uniform fibers with average diameter of 180 nm was 7:3 with ionic conductivity (σi) of 2.9 × 10−3 S/cm. Moreover, the efficiency of DSSCs based on P(AN-co-VAC) as QS electrolyte was enhanced by 8.5 times by addition of PVDF. Finally, a model is proposed based on the EIS analysis.

Components control for high-voltage quasi-solid state dye-sensitized solar cells based on two-phase polymer gel electrolyte

For the quasi-solid-state electrolyte in dye-sensitized solar cells (DSSCs), the selection and optimization of components is a decisive process for high photovoltaic performance while maintaining stability. In this work, a two-phase polymer gel system based on PEO and PEGDME formed by chemical crosslinking is used as quasi-solid electrolyte in DSSCs. Through components of preparation solvent, iodine and GuSCN control, the photoelectric conversion efficiency of QS-DSSCs reaches 7.66%, especially the open-circuit voltage reaches 793 mV due to the self-assembly and ionic conductivity promotion. It lays a solid foundation for probing its potential value of quasi-solid dye-sensitized solar cells.

(SiO2)100-x-Nix (x = 2.5, 10.0) Composite-based photoanode with polymer gel electrolyte for increased dye-sensitized solar cell performance

This work aims on the degradation performance of (SiO2)100-x-Nix (x = 2.5, 10.0) photoanodes incorporating with liquid and gel polymer electrolyte for dye-sensitized solar cell (DSSC). The silica doped with nickel and gel polymer electrolyte was prepared by sol-gel polymerization of tetraethyl orthosilicate and sol-gel polymerization of polyacrylonitrile (PAN), respectively. The utilization of PAN-based gel polymer electrolyte improved the value of open circuit voltage due to its high ionic conductivity and mechanical stability in DSSC. The (SiO2)90.0-Ni10.0-based DSSC utilizing PAN-based gel polymer electrolyte exhibited the highest power conversion efficiency of 2.96%. The field emission electron microscopy images show larger average particle size with greater porosity in the (SiO2)90.0-Ni10.0 thin film. Moreover, the Brunauer-Emmett-Teller analysis determines greater active surface area on (SiO2)90.0-Ni10.0 thin films that indicates more dye molecules may adsorb on the mesoporous photoanode to facilitate electron transport in the DSSC.

Multiply Wrapped Porphyrin Dyes with a Phenothiazine Donor: A High Efficiency of 11.7% Achieved through a Synergetic Coadsorption and Cosensitization Approach.

Photocurrent ( Jsc) and photovoltage ( Voc) are two important parameters for dye-sensitized solar cells (DSSCs) to achieve high power conversion efficiencies (PCEs). Herein, we synthesize four novel porphyrin dyes, XW36-XW39, using an N-phenyl-substituted phenothiazine donor to pursue higher PCE. For XW36 and XW37, the N-phenyl group is wrapped with two ortho-alkoxy chains. In contrast, it is substituted with a para-alkoxy group in XW38 and XW39. The phenothiazine wrapping in XW36 and XW37 induces more serious distortion, which is beneficial for anti-aggregation but unfavorable for the electron transfer from donor to a porphyrin framework. Thus, individual porphyrin dyes XW36 and XW37 exhibit efficiencies of 9.05 and 9.58%, respectively, lower than those of 9.51 and 10.0% achieved for XW38 and XW39, respectively. Besides, the introduction of a methyl group into a benzoic acid acceptor unit is conducive to anti-aggregation and thus improves the Voc and efficiencies. Therefore, higher efficiencies were achieved for XW37 and XW39, compared with XW36 and XW38, respectively. Interestingly, although the individual XW36 dye shows a lowest efficiency among the four dyes, a highest efficiency of 11.7% was obtained for XW36 on the basis of synergetic adsorption with chenodeoxycholic acid and PT-C6 because of simultaneously improved Jsc and Voc, which may be ascribed to the lowest dye-loading amount of XW36 among all of these porphyrin dyes, with the largest vacancy area left on the TiO2 surface available for cosensitizer PT-C6, resulting in a highest Jsc. The high efficiency of 11.7% is one of the highest efficiencies using I-/I3- electrolytes in DSSCs. These results provide an effective strategy for developing efficient DSSCs by the targeted coadsorption and cosensitization of porphyrin sensitizers optimized through introducing a bis( ortho-alkoxy)-wrapped phenyl group into the phenothiazine donor and/or methyl groups into the benzoic acid acceptor unit.

Enhancing the Efficiency of PMMA-Based Quasi-Solid Electrolyte Dye-Sensitized Solar Cells by Ozone Treatment of TiO<sub>2</sub> Thin Films

Enhancing the Efficiency of PMMA-Based Quasi-Solid Electrolyte Dye-Sensitized Solar Cells by Ozone Treatment of TiO<sub>2</sub> Thin Films

Application of deep eutectic solvent from phenol and choline chloride in electrolyte to improve stability performance in dye-sensitized solar cells

In this study, we aim to develop an efficient, eco-friendly and cost-effective electrolyte solvent mixture for Dye-sensitized Solar Cells (DSCs) by using a deep eutectic solvent (DES). A high-purity choline chloride–phenol DES was synthesized and characterized by Fourier-transform infrared and nuclear magnetic resonance spectroscopy; thermogravimetric analysis and differential scanning calorimetry. The resulting product was mixed with acetonitrile, a typical volatile electrolyte solvent, at various ratios for use as electrolyte in DSCs. The photovoltaic parameters (Jsc, Voc, fill factor, efficiency) of these DSC devices were monitored to investigate their long-term performance. The performance of DES-added cells was initially less efficient, but more stable after more than 1000 h, compared to that of the DES-free cells. DES helped to stabilize and improve the photovoltaic performance of DSCs, particularly the short circuit current, due to the effect of the choline and phenol groups of DES binding on the TiO2 surface, as shown by the density functional theory (DFT) calculation. The optimal results were achieved with electrolyte containing 20% DES (efficiency = 6.9% with stable performance for more than 1000 h).

Preparation of quasi-solid-state electrolytes using a coal fly ash derived zeolite-X and -A for dye-sensitized solar cells

We successfully synthesized three zeolites (i.e., zeolite-XF7, zeolite-X&AF, and zeolite-XF12) by new synthesis methods using acetic acid treatment of non-magnetic coal fly ash (FA). The synthesized zeolites were characterized by various surface analysis and used as quasi-solid-state electrolytes for dye-sensitized solar cells (DSSCs). Compared to nano-gel electrolytes based DSSCs showing almost 3.8% of cell efficiency, the enhanced cell efficiencies were obtained from zeolite-XF12 (6.0%), XF7 (5.0%) and X&A (4.8%), respectively. The enhanced performance by zeolite-XF12 was resulted from effective light harvesting properties of quasi-solid-state electrolyte, reduction of resistance at photoanode/electrolyte interface, and decrease in charge recombination.

Performance of chitosan based polymer electrolyte for natural dye sensitized solar cell

Out of the main challenge facing dye sensitized solar cells (DSSCs) is the leakage and vaporization of liquid electrolyte limiting the long term durability of these cells. Therefore, solidification of electrolyte in DSSCs is a crucial research direction. In this work, DSSC was assembled using electrolyte system composed of Chitosan as host polymer, ethylene carbonate as plasticizer, LiI: I2 as redox couple and TiO2 as filler; TiO2 modified with WO3 photoanode to provide inherent energy barrier and anthocyanin as sensitizer. The obtained solar cell conversion efficiency was about 1.8% with fill factor 53% using an irradiation of 100 mW/cm2 at 25 °C. The prepared DSSC is not only stable but also eco friendly due to use of natural polymer and dye. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 630–634, 2019

High conducting nanocomposite electrospun PVDF-HFP/ $$\hbox {TiO}_{2}$$ TiO 2 quasi-solid electrolyte for dye-sensitized solar cell

A high conducting electrospun nanocomposite polymer PVDF-HFP with a crystalline $$\hbox {TiO}_{2}$$ fillers were synthesized and treated with various redox couple electrolytes for dye-sensitized solar cells is reported. The as-spun nanocomposite membranes were characterized using DSC, XRD and FTIR to study the thermal behaviour, crystallinity and interaction between polymer and fillers. The electrolyte uptake behaviour and impedance response of the electrolyte-activated quasi-solid electrolyte membranes were analyzed. A high conductivity of $$1.41\times 10^{-2}\, \text{S cm}^{-1}$$ were achieved for 6 wt% of crystalline $$\hbox {TiO}_{2}$$ fillers with LiI based redox couple and 4-tert-butylpyridine (TBP) as additive. In order to interpret the conducting mechanism and dielectric response involved in the ion dynamics and relaxation of charge carriers of the prepared quasi-solid electrolytes were analysed by the random barrier model along with the effect of electrode polarization and Havarliak–Negami formalism. The photovoltaic performance of all the prepared electrolytes were investigated for all the fabricated DSSC and obtained an efficiency of 5.93% for electrospun nanocomposite (PVDF-HFP/6wt% of $$\hbox {TiO}_{2}$$ ) polymer with LiI based redox couple and TBP additive, as quasi-solid electrolyte.

In situ Evolved Gas Analysis of TMOS-based Gel Electrolytes Containing Guanidinium Thiocyanate for Quasi-solid-state Dye-sensitized Solar Cells by TG-FTIR and TG-MS

A comparative study on thermal stability of hybrid (organic / inorganic) electrolytes for dye-sensitized solar cells (DSSCs) in various ethylene oxide oligomers / silica based gelly matrices, containing also some efficiency-promoter additives is presented. Using thermogravimetry combined with two evolved gas analytical (EGA-FTIR and EGA-MS) techniques, the released gases and volatile decomposition products from the composite electrolytes during dynamic heating programs have been identified and monitored. First methanol (arising from condensation of tetramethoxysilane, TMOS) and acetonitrile (solvent) are evolved followed by elongated release of 4-tert-butylpyridine, than carbonyl sulfide, which is one of the degradation products of guanidinium thiocyanate, and various alkyl iodides, as well as iodine, later various oxidized species with >C=O groups (arising from oxidative degradation of oligo(ethylene glycolic) parts, ammonia (originated from guanidine) have been observed and traced during the accelerated heating tests, before final burning out of the organic residue with CO2 evolution. Thermal behavior of pure guanidinium thiocyanate, one of the most important additives improving thermal stability of Grätzel type solar cells (DSSCs), combined with identification of its eight gaseous decomposition products and their release pattern is also reported.

A thiolate/disulfide liquid crystalline electrolyte for dye-sensitized solar cells: Promotion of the Grotthuss-type charge transport through lamellar nanostructures

Smectic 1-dodecyl-3-methyl-1H-imidazol-3-ium 1-methyl-1H-tetrazole-5thiolate ([C12MIm][T]) has been prepared for dye-sensitized solar cells (DSSCs). The electrolyte consisting of [C12MIm][T] and di-5-(1-methyltetrazole) disulfide (T2) with mole ratio 2:1 exhibited smectic A (SA) liquid crystal phase over a temperature range from 12.5–75.5 °C. A bilayer nanostructure formed in the SA phase and the T−/T2 redox couple was intercalated between the smectic layers. Photovoltaic characterization revealed that the power conversion efficiency of the smectic T−/T2 DSSC increased with the increase in temperature and reached 4.1% at 70 °C under simulated AM1.5G solar light. Regression analysis of temperature dependent charge diffusion coefficients and viscosities suggested that the charge transport in the T−/T2 electrolyte was dominated by the Grotthuss-type exchange reaction. The lamellar nanostructure of T−/T2 promoted the Grotthuss-type charge transport and improved the DSSC performance. The ordered arrangement of the redox couple offers an effective way to enhance the charge transport for the DSSC electrolytes unfavorable for physical ion diffusion.

Application of response surface methodology in assessing the effect of electrospinning parameters on the morphology of polyethylene oxide/polyacrylonitrile blend nanofibers containing graphene oxide

Electrospun polyethylene oxide/polyacrylonitrile/graphene oxide (PEO/PAN/GO) membranes were produced for using as polymer electrolytes in dye-sensitized solar cells. The effects of material and process parameters on the diameter of the fibers were evaluated using Box–Behnken experimental design to obtain a quantitative relationship between selected parameters (namely GO content, solution concentration, feed rate) and responses (nanofibers diameters and their standard deviation). The importance of the parameters and their interactions were investigated through the analysis of variance. The model was consequently used to find the optimal conditions that yield the minimum nanofiber diameter. The morphology and nanofiber diameter were investigated by scanning electron microscopy. Fibers with diameters ranging from 103 to 340 nm were obtained. It was observed that the nanofiber diameter increased with solution concentration and feed rate. The GO incorporation caused a reduction of the nanofiber diameters. Nanofibers with smaller diameters and standard deviations could be obtained at lower solution concentrations and feed rates. Based on the desirability function, the optimized factors for minimum nanofiber diameter were found as 1 wt% GO, 17 w/v% solution concentration and 1 ml/h feed rate. Finally, the thermal and electrochemical properties of the optimized sample were compared with the pristine PEO/PAN membrane electrolyte. The measured electrolyte uptake and ionic conductivity of the membranes showed a significant improvement in the presence of GO nanosheets.

The Effect of Difference Molar Ratios of Dibromo-EDOT as Hole Transporting Material for Solid State Dye-Sensitized Solar Cells

The dye-sensitized solar cells (DSSCs) are one of the promising organic photovoltaic cells due to their low cost, flexibility, and relatively good efficiency. Nevertheless, utilization of liquid electrolyte in DSSCs brings practical problems for commercialization, which leads to solid-state dye-sensitized solar cells (ssDSSCs), that based on organic conducting polymers or inorganic p-type semiconductors as hole transport materials (HTM). A one-side ssDSSCs fabricated here, with a conductive polymer Dibromo-EDOT as an HTM, and also check ssDSSCs efficiency by variation of the HTM concentrations. The morphology of cells examined through SEM, and intensity-modulated photocurrent/voltage spectroscopy, measurements were used to elucidating the electrochemical properties of ssDSSCs. We also optimize the blocking layer thickness and different molar ratios of HTM for the best efficient ssDSSCs.

Highly catalytic and reflective dual-phase nickel sulfide electrodes for solar energy conversion

A simple and practical method is presented for the fabrication of mirror-like reflective nickel sulfide (NiS) films via a hydrothermal reaction to serve as efficient transition metal chalcogenide catalysts. The NiS films on fluorine-doped tin oxide (FTO) glass substrates exhibit dual-phase crystalline structure with tunable α-NiS/Ni3S4 composition. The α-NiS/Ni3S4 ratio could be tuned by varying the concentration of the sulfur source, thioglycolic acid in the reaction mixture. The key role of thioglycolic acid is to control the morphology and crystal phase structure as well as determine the nickel to sulfur ratio. The NiS films, especially those fabricated with an adequate amount of the sulfur source, show multifunctional properties with significantly improved electrical conductivity, catalytic activity, and light reflectance due to the multiple layers of the stacked structure. Owing to the unique features of the fabricated films, solid polymer electrolyte dye-sensitized solar cells (DSSC) based on NiS counter electrodes exhibit photovoltaic energy conversion efficiency of 6.22%, which is much higher than that achieved with commercial Pt counter electrodes (5.42%). This superior performance indicates the immense potential of the NiS film as an efficient catalyst alternative for DSSCs.

Dye-sensitized solar cells using deep eutectic solvents mixed with ethanol as an effective electrolyte medium

This research aims to develop a new type of electrolyte for dye-sensitized solar cells (DSCs) which can be produced in cost-effective and large scale. DSCs using deep eutectic solvents (DESs) mixed with ethanol (50% w/w DES content), as an electrolyte medium, was studied herein for the first time. Ten types of DESs were synthesized and three among them were potential candidates for DSC electrolytes. Compared to toxic and volatile organic solvents, this mixed solvent is more eco-friendly and inexpensive. According to J-V curve measurements, DSCs that used DES-ethanol medium showed promising photovoltaic performance.

Element substitution of kesterite Cu2ZnSnS4 for efficient counter electrode of dye-sensitized solar cells

Development of cost-effective counter electrode (CE) materials is a key issue for practical applications of photoelectrochemical solar energy conversion. Kesterite Cu2ZnSnS4 (CZTS) has been recognized as a potential CE material, but its electrocatalytic activity is still insufficient for the recovery of I−/I3− electrolyte in dye-sensitized solar cells (DSSCs). Herein, we attempt to enhance the electrocatalytic activity of kesterite CZTS through element substitution of Zn2+ by Co2+ and Ni2+ cations, considering their high catalytic activity, as well as their similar atomic radius and electron configuration with Zn2+. The Cu2CoSnS4 (CCTS) and Cu2NiSnS4 (CNTS) CEs exhibit smaller charge-transfer resistance and reasonable power conversion efficiency (PCE) (CCTS, 8.3%; CNTS, 8.2%), comparable to that of Pt (8.3%). In contrast, the CZTS-based DSSCs only generate a PCE of 7.9%. Density functional theory calculation indicate that the enhanced catalytic performance is associated to the adsorption and desorption energy of iodine atom on the Co2+ and Ni2+. In addition, the stability of CCTS and CNTS CEs toward electrolyte is also significantly improved as evidenced by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy characterizations. These results thus suggest the effectiveness of the element substitution strategy for developing high-performance CE from the developed materials, particularly for multicomponent compounds.

Effect of different imidazolium-based ionic liquids on gel polymer electrolytes for dye-sensitized solar cells

Host polymer electrolytes are prepared using poly(ethylene oxide) (PEO) as a polymer, ethylene carbonate (EC) and propylene carbonate (PC) as solvents, sodium iodide (NaI) as salt, and iodine (I2) and with either one of the ionic liquids (ILs) which are 1-methyl-3-propylimidazolium iodide (MPII), 1-butyl-3-methylimidozium (BMII), and 1-hexyl-3-methylimidozium iodide (HMII) in each gel polymer electrolyte. The ionic conductivity of the gel polymer electrolytes (GPEs) was measured by electrochemical impedance spectrometer (EIS). The ionic conductivity of GPEs increased with the presence of ionic liquids (ILs). At room temperature, the dielectric behaviors of the GPEs were studied. The highest ionic conductivity of 9.41 mS cm−1 is achieved after addition of MPII ionic liquid. Meanwhile, Fourier-transform infrared and X-ray diffraction studies confirm complexation between PEO polymer, NaI salt, and ionic liquids (MPII, BMII, and HMII). Dye-sensitized solar cells (DSSCs) were fabricated using polymer electrolytes and studied under Sun simulator. The DSSC using MPII ionic liquid shows the highest efficiency of 9.35%.

Solid state dye sensitized solar cells with polyaniline-thiourea based polymer electrolyte composition

The quest for cost effective and efficient solid-state electrolytes is a primary goal for dye sensitized solar cells (DSSCs). The present study describes an experimental approach of synthesizing simple composite electrolytes from iodide-triiodide ions (I−/I3−) incorporated into a polyaniline/thiourea matrix for solid-state DSSC applications. This electrolyte composition can be effectively used to decrease the probability of recombination at the TiO2/electrolyte interface and increase the catalytic process of I3− reduction at the electrolyte/counter electrode interface. The application of the optimized electrolyte in DSSC results in increased open-circuit voltage as well as short circuit current density, thereby increasing the overall efficiency by 73% as compared to the reference electrolyte. The present composition can prove to be a promising redox medium for solid state DSSCs.