Quasi-solid State Dye-sensitized Solar Cells Research Articles

Synthesis and Photovoltaic Performance of Ionic Dyes for Quasi-Solid State Dye-Sensitized Solar Cells

We prepared the ionic dyes and investigated their electrochemical properties and photosensitizing performances in the quasi-solid state dye-sensitized solar cells (QS-DSSCs). The LUMO energy level of ionic dye with carbazole moiety is higher than that of the dyes with phenothiazine and triphenylamine chromophore, resulting in highest power conversion efficiency (PCE) in the QD-DSSC. Compared with Ru-complex sensitizer, the ionic dyes showed relatively low photovoltaic performance in the QS-DSSCs, originating in lower LUMO energy level. The effect of Li+ion in the quasi-solid state electrolyte on the photovoltaic characteristics of QS-DSSCs was investigated in order to confirm the correlation between the conduction band of TiO2electrode and LUMO energy level of photosensitizers. The conduction band of TiO2electrode could be reduced by adding the Li+ion in the electrolyte, attributing for the enlargement of PCE value in the QS-DSSC.

Ethyl cellulose and functionalized carbon nanotubes as a co-gelator for high-performance quasi-solid state dye-sensitized solar cells

Long term device stability and high power conversion efficiency (PCE) are important for practical application of dye-sensitized solar cells (DSCs). Here, we report the use of ethyl cellulose (EC) and acid functionalized multi-walled carbon nanotubes (oMWCNTs) as a co-gelator to gel organic solvents and the application of these gels for quasi-solid state DSCs. The gels are formed by blending EC and oMWCNTs with methoxypropionitrile (MPN) and acetonitrile (ACN). The loadings of EC and oMWCNTs can be as low as 4 wt% and 1.5 wt%, respectively, for the gel formation. The total minimum gelator loading of EC and oMWCNTs is lower than that with EC alone. In the absence of oMWCNTs, the EC loading must be more than 12 wt% for the gel formation. Gel electrolytes were prepared by adding iodine, 1-methyl-3-propylimidazolium iodide (PMII), guanidinium thiocyanate and 4-tert-butyl pyridine into the EC-oMWCNT/ACN-MPN gels, and they were used to fabricate quasi-solid state DSCs. The optimal PCE of the gel DSCs was 6.97% under AM1.5G illumination, quite close to that of control liquid DSCs, while the gel DSCs have better long term stability than their liquid-state counterparts. The former retains more than 98% of the initial PCE after 30 days, whereas the PCE of the latter decreases to about 80%.

The Preparation and Photovoltaic Properties of Quasi-solid State Dye-Sensitized Solar Cells Containing Long Wavelength Absorbing Squaraine Dye

The performance of the quasi-solid state DSSC composed of long wavelength absorbing squaraine dye was investigated and compared with that of ruthenium-complex (N3) sensitized DSSC. In spite of the narrow sensitizing region of SQ dye from 500 nm to 750 nm, the quasi-solid state DSSCs gave a moderate solar energy-to-electricity conversion efficiency under AM 1.5 G irradiation (100 mW/cm2) of 2.34%, a short-circuit current density of 5.56 mA/cm2, with an open-circuit voltage of 650 mV.

Investigation of the role of anions in hydrotalcite for quasi-solid state dye-sensitized solar cells application

In recent research in clean energy applications, clay has gained significant interest, especially as a gelator in dye-sensitized solar cells (DSSCs), for its capability to resolve the leakage issue of liquid electrolyte. In this paper, anionic hydrotalcite is utilized as a gelator to assist the formation of gel electrolyte in DSSCs. Three types of hydrotalcite with exchangeable anions, viz. NO3− (CL-N), CO32− (CL-C) and SO42− (CL-S), were synthesized with similar morphologies via the co-precipitation method. It is observed that the gel formation of hydrotalcite strongly depends on the exchangeable anions present in the hydrotalcite. The objective of this work is to understand the effect of hydrotalcite anions on the photovoltage and the photocurrent in the gel electrolyte through electrochemical analysis. With increasing ion affinity, the Voc increases. This is attributed to Li+ intercalation with hydrotalcite compound resulting in the elevation of the conduction band of TiO2. With increasing ion affinity, the Jsc decreases. This is attributed to the decreasing diffusion coefficient of triiodide and the increasing difficulty in the injection process. For anions with low ion affinity in hydrotalcite, the diffusion of the redox couple is not significantly affected by the high viscosity of the gel. Furthermore, the study indicates that proper selection of hydrotalcite compounds not only produces a quasi-solid gel electrolyte, but also increases the efficiency of the solar cells: the device performance was improved from 7.8% (liquid electrolyte) to 8.4% (hydrotalcite gel electrolyte).

A novel quasi-solid state dye-sensitized solar cell fabricated using a multifunctional network polymer membrane electrolyte

A series of liquid junction dye-sensitized solar cells (DSCs) was fabricated based on polymer membrane-encapsulated dye-sensitized TiO2 nanoparticles, prepared using a surface-induced cross-linking polymerization reaction, to investigate the dependence of the solar cell performance on the encapsulating membrane layer thickness. The ion conductivity decreased as the membrane thickness increased; however, the long term-stability of the devices improved with increasing membrane thickness. Nanoparticles encapsulated in a thick membrane (ca. 37 nm), obtained using a 90 min polymerization time, exhibited excellent pore filling among TiO2 particles. This nanoparticle layer was used to fabricate a thin-layered, quasi-solid state DSC. The thick membrane prevented short-circuit paths from forming between the counter and the TiO2 electrode, thereby reducing the minimum necessary electrode separation distance. The quasi-solid state DSC yielded a high power conversion efficiency (7.6 → 8.1%) and excellent stability during heating at 65 °C over 30 days. These performance characteristics were superior to those obtained from a conventional DSC (7.5 → 3.5%) prepared using a TiO2 active layer with the same thickness. The reduced electrode separation distance shortened the charge transport pathways, which compensated for the reduced ion conductivity in the polymer gel electrolyte. Excellent pore filling on the TiO2 particles minimized the exposure of the dye to the liquid and reduced dye detachment.

Printable electrolytes for highly efficient quasi-solid-state dye-sensitized solar cells

Novel polymer gel electrolytes (PGEs) with high ionic conductivity based on polyvinyl (acetate-co-methyl methacrylate) [P(VA-co-MMA)] were prepared by soaking porous copolymers in an organic electrolyte solution [acetonitrile (ACN) or 3-Methoxypropionitrile (MPN)] that contained an I3−/I− as redox couple. Quasi-solid-state dye-sensitized solar cells (QS-DSSCs) were fabricated with the PGEs, and the best PGE was selected and optimized. Using the best PGE and under 100mWcm−2 light illumination (AM1.5), the QS-DSSC achieved a high photovoltaic conversion efficiency of 9.10%, nearly the same as that for the DSSC based on the original liquid electrolyte. Introduction of TiO2 nanoparticles into the PGEs further enhanced PGEs ionic conductivity and the conversion efficiency to 9.40%. Subsequent results revealed that our QS-DSSC had a better stability because it could maintain 96.7% of its initial efficiency after long-time (1000h) exposure to simulative sunlight. Besides, for the first time, large-area QS-DSSCs were fabricated by screen printing of PGE, other than the traditional vacuum injection that was infeasible for the viscous gel electrolyte. Finally, our 5cm×7cm QS-DSSC sub-module exhibited a conversion efficiency higher than 4%.

The production of organogels using graphene oxide as the gelator for use in high-performance quasi-solid state dye-sensitized solar cells

We report the formation of organogels of 3-methoxypropionitrile (MPN) using graphene oxide (GO) as the gelator and the use of these gels as the quasi-solid state electrolyte of dye-sensitized solar cells (DSCs). GO–MPN gels are prepared by mechanically grinding or ultrasonicating GO in MPN. The GO sheets form 3-dimensional solid networks in the gels, which hold the MPN solvent. The GO loading can be as low as 2.5wt.% for the gel formation. Gel electrolytes were prepared by dispersing I2, 1-methyl-3-propylimidazolium iodide, guanidine thiocynate and 4-tert butyl pyridine into GO–MPN gels, and these were used for DSCs. The GO sheets can be fragmented into small pieces by ultrasonication, and smaller GO sheets can lead to a higher diffusion constant of the triiodide and a higher photovoltaic efficiency for the DSCs. DSCs with a GO–MPN gel electrolyte exhibit a photovoltaic efficiency of 6.70% under AM 1.5G illumination (100mWcm−2), quite close to that (7.18%) of the control liquid DSCs.

Chemically Crosslinked Copolymer Electrolytes Based on Imidazole for Quasi-Solid State Dye-Sensitized Solar Cells

In this study, gel electrolytes based on poly(1-vinyl imidazole-co-elthylene glycol methyl ether acrylate) (P(VIm-co-EGMEA)) as backbone polymer and 1,5-diiodopentane (I(CH2)5I) as crosslinker were used for quasi-solid state dye-sensitized solar cells (QS-DSSCs). Chemically crosslinked gel electrolyte using certain concentration of P(VIm-co-EGMEA) and I(CH2)5I, DSSCs were fabricated and their photovoltaic performances measured by using a Solar Simulator. In order to characterize the electrolytes, resistance of the DSSCs and ionic conductivity of the electrolyte (0.035M of P(VIm-co-EGMEA)) was examined by Electrochemical Impedance Spectroscopy (EIS) and the nanopore-filled electrolytes into the nanocrystalline TiO2 film were investigated by using a Scanning Electron Microscope (SEM).

Enhancing in the performance of dye-sensitized solar cells by the incorporation of functionalized multi-walled carbon nanotubes into TiO2 films: The role of MWCNT addition

a b s t r a c t TiO2-MWCNT composite electrodes were prepared by a direct mixing method. The presence of acid- treated multi-wall carbon nanotubes (MWCNT-COOH) into the titanium dioxide (TiO2) photoanode was investigated by Raman spectroscopy and X-ray diffraction (XRD). The morphological properties of the composite photoanodes were analyzed by field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The performance of quasi-solid state dye-sensitized solar cells (DSSC) using TiO2-MWCNT photoanodes was dependent on the MWCNT loading. Compared with a DSSC based on conventional TiO2 electrodes, the TiO2-MWCNT film containing 0.02 wt.% of carbon nanotubes pro- vided an increase of ca. 30% in device's efficiency, which was attributed to an enhanced short-circuit current density (Jsc). The improvement on Jsc was correlated with an enhanced interconnectivity between MWCNT-COOH and TiO2 nanoparticles. The carbonaceous materials introduced an alternative electrical conduction pathway which facilitates rapid electron transport in the photoelectrode, as suggested from Kelvin probe force microscopy (KPFM) measurements. At high MWCNT loading, we observed that the energy conversion efficiency decreased due to energy losses from the optical absorption of carbonaceous materials, and also due to an increase in charge recombination.

A comparative study of charge transport in quasi-solid state dye-sensitized solar cells using polymer or nanocomposite gel electrolytes

To improve the photovoltaic and durability performance of quasi-solid dye-sensitized solar cells (DSCs), we added selected gelators to the liquid electrolyte. Metal-oxide nanoparticles or fluorine polymers were employed to solidify 3-methoxypropionitrile-based liquid electrolytes containing an ionic liquid, 1,2-dimethyl-3-propyl imidazolium iodide, as a source of iodide. The electrochemical impedance spectroscopy and cyclic voltammetry were employed to study the kinetics of electrochemical and photoelectrochemical processes, including the elucidation of the electronic and ionic processes occurring in the various quasi-solid-state solar cells. Among tested gelators, a cell with TiO2 solidified electrolyte (P25, 17.5wt%) exhibited the best photovoltaic performance with power conversion efficiency 7.65% under simulated sunlight (100mWcm−2). The DSCs with a TiO2 solidified electrolyte showed endurance of stability superior to that of a pure liquid electrolyte.

Improved performance using a plasticized polymer electrolyte for quasi-solid state dye-sensitized solar cells

A PEO/P(VDF-HFP) polymer-blend electrolyte is modified by different amounts of LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfone)imide, LiTFSI). Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) are carried out to examine the configuration changes of the polymer electrolyte. LiTFSI acts as a plasticizer influencing the ionic conductivity of the LiTFSI-modified polymer electrolyte, and improves the short-circuit photocurrent effectively. The electrochemical impedance spectroscopy (EIS) indicates that the intercalation or adsorption of overdose Li+ to the TiO2 photoanode surface positively changes the Fermi energy level and the conduction band. This improves the interface recombination in the DSSC and reduces the open-circuit voltage. With moderate LiTFSI content (0.05g, nKI/nI2=7:1) modification, the DSSC exhibits a 1.6mAcm−2 improvement of current density and an improved performance of 5.03% compared with 4.51% of the original DSSC.

Controlled Dissolution of Polystyrene Nanobeads: Transition from Liquid Electrolyte to Gel Electrolyte

The widespread commercialization of dye-sensitized solar cells (DSSCs) remains limited because of the use of highly volatile liquid electrolytes. Recently, gel-type quasi-solid electrolytes containing a polymer additive or inorganic nanomaterial have shown promising results in terms of the cell efficiency. However, most gel electrolytes have serious obstacles for pore-filling because of their high viscosity. Herein, we report the first observation of the transition from a liquid to a gel electrolyte after filling the cell with the liquid electrolyte using the controlled dissolution of polystyrene nanobeads on the counter electrode, suggesting that the pore-filling problem can be diminished in quasi-solid state DSSCs. The time-resolved solidification allows for the preparation of the gel electrolyte without interfering with the cell performance. The optimal DSSC composed of the gel electrolyte exhibits almost the same power conversion efficiency as the liquid electrolyte based DSSC when measured using an AM1.5G solar simulator at 100 mW/cm(2) light illumination. Moreover, the long-term stability of the DSSC was greatly improved.

Enhanced Light Harvesting from Först-Type Resonance Energy Transfer in the Quasi-Solid State Dye-Sensitized Solar Cells

The demonstrated Först-type resonance energy transfer (FRET) is demonstrated in quasi-solid type dye-sensitized solar cells between organic fluorescence materials as an energy donor doped in polymeric gel electrolyte and a ruthenium complex as an energy acceptor on the surface of TiO2. Strong spectral overlap of emission/absorption of the energy donor and acceptor is required to obtain high FRET efficiency. The judicious choice of the energy donor allows the enhancement of the light harvesting characters of the energy acceptor (N3) in quasi-solid dye sensitized solar cells which increases the power conversion efficiency by 25% compare to that of a pristine cell. The optimized cell architecture fabricated with the quasi-solid type electrolyte containing fluorescence materials shows a maximum efficiency of 5.08% with a short-circuit current density (J(sc)) of 12.63 mA/cm2, and an open-circuit voltage (V(oc)) of 0.70 V under illumination of simulated solar light (AM 1.5, 100 mW/cm2).

Application of Pt sputter-deposited counter electrodes based on micro-patterned ITO glass to quasi-solid state dye-sensitized solar cells

The effects of the Pt catalyst sputter deposited on the patterned ITO glass (SD-Pt/pITO) on the photovoltaic properties and charge-transfer characteristics at the Pt/electrolyte interface of dye-sensitized solar cells (DSSCs) are studied and compared with those of a conventional Pt counter electrode deposited by thermal reduction on fluorine-doped tin oxide (FTO) glass (TD-Pt/FTO). The DSSC with the SD-Pt/pITO (sample cell) shows a lower charge-transfer resistance than that of the DSSC with the TD-Pt/FTO (reference cell), which leads to an improvement of its fill factor by about 7.6%. The long-term durability test performed for 1000 h at room temperature reveals that the sample cell retains up to 99% of its energy conversion efficiency, while that of the reference cell is degraded by about 7.2%.

Natural dye-sensitized solar cells using pigments extracted from <italic>Syzygium guineense</italic>

A study on dye-sensitized solar cells (DSSCs) with extracts of Syzygium guineense as sensitizer is reported for the first time. DSSCs were assembled using natural dye extracted from Syzygium guineense as sensitizer. The photoelectrochemical performance of the quasi-solid state DSSCs based on the ethanol extract dye showed VOC of 0.506 V and JSC of 2.03 mAcm−2; and a power conversion efficiency of 0.51%. UV-vis spectroscopy studies of light absorption of the natural dye were done. Furthermore, the ethanol extract obtained from Syzygium guineense was further purified stepwise through solvent-solvent extraction. The photoelectrochemical performance for the extracts with different solvents indicated that the individual components have synergistic effect in the performance of the DSSC.

Enhanced light-harvesting efficiency by Förster resonance energy transfer in quasi-solid state DSSC using organic blue dye

We have demonstrated Förster resonance energy transfer (FRET) between organic fluorescent materials (as an energy donor) doped in fluorinated-polymer gel electrolyte and organic blue dye (as an energy acceptor on TiO2 surfaces in dye-sensitized solar cells (DSSCs)). The judicious choice of the energy donor and electron acceptor allows a strong spectral overlap of the emission/absorption of energy donor and acceptor, which could enhance the light-harvesting characteristics of the energy acceptor in quasi-solid DSSCs. The power conversion efficiency of DSSCs containing fluorescent material in a quasi-solid electrolyte increased by 19% over a pristine cell. The optimized cell architecture fabricated with the quasi-solid state DSSC containing the organic blue dye on a photoanode shows a maximum efficiency of 2.15%, with a short-circuit current density (Jsc) of 4.32mAcm−2 and an open-circuit voltage (Voc) of 0.68V under illumination of simulated solar light (AM 1.5G, 100mWcm−2).

Tetrahexylammonium Iodide Containing Solid and Gel Polymer Electrolytes for Dye Sensitized Solar Cells

TiO2 dye sensitized solar cells (DSSCs) are emerging as an alternative technology to photovoltaic junction devices. DSSCs conventionally use liquid-type electrolytes but solid and gel polymer electrolytes are more promising due to many advantages. However, their conductivity needs to be enhanced in order to make them useful in practical device applications. In this work, an iodide ion conducting polymer electrolyte was prepared using polyacrylonitrile (PEO), tetrahexylammonium iodide salt with ethylene carbonate and propylene carbonate plasticisers. The salt composition was varied to find the optimum conductivity. The sample containing 120% salt with respect to PEO weight showed the highest conductivity. This optimum electrolyte showed a glass transition at -102.3°C and an ambient temperature conductivity of 2.1×10-3 S cm−1 at 30°C. The optimized gel electrolyte was used in a quasi solid-state DSSC and a ISC of 9.37 mA cm-2, a VOC of 696 mV and an efficiency of 2.8% were achieved under irradiation of 1000 W m−2. In addition, a solid polymer electrolyte was fabricated using the same salt with polyethylene oxide host polymer and ethylene carbonate. The salt composition was varied to obtain the highest conductivity and the best performing sample with composition 65% salt with respect to PEO weight showed a conductivity of 4.7×10-4 S cm-2 at 30°C. This electrolyte was used in a DSSC and it showed a ISC of 1.26 mA cm-2, a VOC of 745 mV and efficiency of 0.6%.

Influence of Polymer Gel Electrolyte on the Performance of Dye-Sensitized Solar Cells Analyzed by Electrochemical Impedance Spectroscopy

The effects of gel electrolyte polymer matrix structure and composition on the photovoltaic properties of quasi-solid state dye-sensitized solar cells(DSSCs) were investigated using two series of copolymers,poly(hydroxy ethyl methacrylate-N-vinyl) pyrrolidone P(HEMA-NVP) and poly(methyl methacrylateN-vinyl pyrrolidone) P(MMA-NVP),by electrochemical impedance spectroscopy(EIS).P(HEMA-NVP) copolymers with various crosslinking agent and N-vinyl pyrrolidone(NVP) contents,as well as P(MMA-NVP)copolymers with various NVP content,absorbed liquid electrolyte to form gel electrolytes HGelI,HGelII,and MGel,respectively.It was found that with increasing copolymer P(HEMA-NVP) crosslinking agent content,from 0.1 to 0.6%(w),the power conversion efficiency(η) of DSSCs based on HGelI initially increased and then decreased.A maximum conversion efficiency of 5.54% at 100 mW.cm-2 was observed when crosslinker content was 0.4%(w).Meanwhile,we compared the parameters of DSSCs based on HGelII with those of DSSCs based on MGel.The conversion efficiencies of the former,which contained hydroxy groups,were all higher than those of the latter,while the open circuit voltages(Voc) of the latter were larger than those of the former.DSSCs assembled with HGelII with a HEMA content of 60% exhibited the highest conversion efficiency,at 100 mW.cm-2.Electrochemical impedance spectroscopy(EIS) investigations showed that copolymer crosslinking structure affected the internal resistance and ionic conductivity of the resulting DSSCs,while addition of hydroxy groups decreased the interfacial resistance.Thus,the photovoltaic performance of DSSCs can be improved by tuning the crosslinking structure and the hydroxy content of the copolymer.

Quasi-Solid State Dye-Sensitized Solar Cells Based on the Novel Crosslinked Polymer Electrolyte

A quasi-solid-state three-dimensionally crosslinked poly(citric acid-ethylene glycol)(PCE)/ LiI/I 2 polymer electrolyte has been prepared using biodegradable PCE synthesized via a crosslinking reaction between citric acid(CA)and oligo-polyethylene glycol(PEG)(average molecular weight Mw = 200,400,1000,2000)as a matrix.The molecular structure of the PCE matrix,micro-morphology of polymer electrolyte,and the state of conductive ion-pairs in the electrolyte were characterized by infrared(IR)spectrum, 1H nuclear magnetic resonance( 1H-NMR),and Raman spectroscopy,as well as scanning electron microscopy(SEM).The ionic diffusion coefficient and conductivity of polymer electrolytes and the output current-voltage(I-V)properties of the cells were investigated via linear sweep voltammetry.The results reveal that PEG molecular weights influence the mesh morphology and theabsorbent properties of the PCE matrix,which influences the polymer electrolyte ionic conductive performance and the photoelectric performance of the cells.As PEG molecular weights increased from 200,400,1000 to 2000,the PCE matrix mesh structure became looser,the liquid electrolyte uptake of the matrix increased,and the transition activation energies of I - 3 in the swollen PCE matrix decreased,which led to an increase in the electrolyte conductivity and the short circuit photocurrent densities of the cells accordingly.The photoelectric conversion efficiencies of the cells assembled by the four polymer electrolytes above were 3.26%,3.34%,4.26%,and 4.89%,respectively,under an incident light intensity of 60 mW·cm -2 .

Investigation of Ion Transport and its Effect on the Photovoltaic Performance in the Quasi-Solid State Dye-Sensitized Solar Cells

In this paper, we investigated the diffusion behaviour of in the mixture of ethylene carbonate (EC) and propylene carbonate (PC) electrolyte solidified by polyacrylonitrile ( PAN, molecular weight: 60,000). The effect of the ion diffusion process on the photoelectric properties was also studied. The ion diffusion process was found to be the main factor to the photoelectric properties in the quasi-solid state dye-sensitized solar cells. Some ideas, such as the optimization of the thickness and the concentration of in the electrolyte, were proposed to improve the transport velocity of.