A highly efficient electric additive for enhancing photovoltaic performance of dye-sensitized solar cells

N-cetylpyridinium iodide (N-CPI) as a new electric additive for enhancing photovoltaic performance of the dye-sensitized solar cell (DSSC) was studied. It showed high efficiency for enhancing both the open-circuit voltage and the short-circuit current density of DSSC when the suitable amount of N-CPI as 0.02 M was added in liquid electrolyte. The energy conversion efficiency of DSSC increased from 4.429% to 6.535%, with 47.55% enhancement. Therefore, it is a highly efficient electric additive for DSSC. The intrinsic reason is owing to the special molecular structure of N-CPI, which contains two different polarity groups. As a surfactant, N-CPI could form ordered arrangement in liquid electrolyte, which affects the diffusing ability and the redox reaction of I^?/I ₃ ^? , and further affects the photovoltaic performance of DSSC.     

Ionic Liquid Based Electrolyte with Mesoporous Silica SBA-15 as Framework for Quasi-solid-state Dye-sensitized Solar Cells

Quasi-solid-state electrolytes were fabricated with mesoporous silica SBA-15 as a framework material. Ionic conductivity measurements revealed that SBA-15 can enhance the conductivity of the quasi-solid-state electrolyte. The diffusion coefficients of polyiodide ions such as Ⅰ3ˉ and Ⅰ5ˉ which were confirmed by Raman spectroscopic measurement, were about twice larger than that of I-. The optimized photoenergy conversion efficiency of dye-sensitized solar cells （DSSC） with the quasi-solid-state electrolyte was 4.3% under AM 1.5 irradiation at 75 mW·cm^-2 light intensity.     

Ionic liquid crystal-based electrolyte with enhanced charge transport for dye-sensitized solar cells

A room temperature ionic liquid crystal,1-dodecyl-3-ethylimidazolium iodide(C12EImI),and an ionic liquid,1-decyl-3-ethylimidazolium iodide(C10EImI),have been synthesized,characterized and employed as the electrolyte for dye-sensitized solar cells(DSSC).The physicochemical properties show that a smectic A(SmA)phase with a lamellar structure is formed in C12EImI.Both C12EImI and C10EImI have good electrochemical and thermal stability facilitating their use in DSSC.The steady-state voltammograms reveal that the diffusion coefficient of I3–in C12EImI is larger than that in C10EImI,which is attributed to the existence of the SmA phase in C12EImI.Because the iodide species are located between the layers of imidazolium cations in C12EImI,exchange reaction-based diffusion is increased with a consequent increase in,the overall diffusion.The electrochemical impedance spectrum reveals that charge recombination at the dyed TiO2/electrolyte interface of a C12EImI-based DSSC is reduced due to the increase in I3–diffusion,resulting in higher open-circuit voltage.Moreover,both short-circuit current density and fill factor of the C12EImI based DSSC increase,as a result of the increasing transport of I3–in C12EImI.Consequently,the photoelectric conversion efficiency of C12EImI-based DSSC is higher than that of the C10EImI–based DSSC.     

Recent Advances of Cobalt(II/III) Redox Couples for Dye‐Sensitized Solar Cell Applications

In recent years dye‐sensitized solar cells (DSSCs) have emerged as one of the alternatives for the global energy crisis. DSSCs have achieved a certified efficiency of >11% by using the I^?/I₃^? redox couple. In order to commercialize the technology almost all components of the device have to be improved. Among the various components of DSSCs, the redox couple that regenerates the oxidized sensitizer plays a crucial role in achieving high efficiency and durability of the cell. However, the I^?/I₃^? redox couple has certain limitations such as the absorption of triiodide up to 430 nm and the volatile nature of iodine, which also corrodes the silver‐based current collectors. These limitations are obstructing the commercialization of this technology. For this reason, one has to identify alternative redox couples. In this regard, the Co(II/III) redox couple is found to be the best alternative to the existing I^?/I₃^? redox couple. Recently, DSSC test cell efficiency has risen up to 13% by using the cobalt redox couple. This review emphasizes the recent development of Co(II/III) redox couples for DSSC applications.     

Rubbery copolymer electrolytes containing polymerized ionic liquid for dye-sensitized solar cells

A novel type of random copolymer comprised of a polymerized ionic liquid, poly(1-((4-ethenylphenyl)methyl)-3-butyl-imidazolium iodide) (PEBII), and amorphous rubbery poly(oxyethylene methacrylate) (POEM) was synthesized and employed as a solid electrolyte in an I₂-free dye-sensitized solar cell (DSSC). The copolymer electrolytes deeply infiltrated into the nanopores of mesoporous TiO2 films, resulting in improved interfacial contact of electrode/electrolyte. The glass transition temperature (T _g) of the PEBII–POEM (?23 °C) was lower than that of PEBII homopolymer (?4 °C), indicating greater chain flexibility in the former. However, the DSSC efficiency of PEBII–POEM (4.5 % at 100 mW/cm²) was lower than that of PEBII (5.9 %), indicating that ion concentration is more important than chain flexibility. Interestingly, upon the introduction of ionic liquid, i.e., 1-methyl-3 propylimidazolium iodide, the efficiency of PEBII remained almost constant (5.8 %), whereas that of PEBII–POEM was significantly improved up to 7.0 % due to increased I^? ion concentration, which is one of the highest values for I₂-free DSSCs.     

The conducting polymer electrolyte based on polypyrrole-polyvinyl alcohol and its application in low-cost quasi-solid-state dye-sensitized solar cells

The effect of polypyrrole (PPy) on the polyvinyl alcohol (PVA)-potassium iodide (KI)-iodine (I₂) polymer electrolytes has been investigated and optimized to use in a dye-sensitized solar cell (DSSC). The different weight ratios of PVA: PPy (93: 2, 91: 4, 89: 6, 87: 8, and 85: 10 wt%) polymer electrolytes (PE) were prepared by solution casting. Structural, complex formation and surface roughness of the prepared electrolytes was confirmed by X-ray diffraction, FTIR, and atomic force microscopy (AFM) respectively. Conductivity plots of all polymer films showed increasing trend with temperature and concentration of PPy. The activation energy of the optimized system found to be 0.871 kJ mol^?1. UV-visible spectrum was adopted to characterize the absorption spectra of the material revealed that increase in the absorbance with increasing PPy content and shifting the absorbance maximum towards lower energy. The indirect band gap decreased from 3.78 to 2.14 eV and direct band gap decreased from 3.88 to 2.71 eV. The EIS analyses revealed the lower charge transfer resistance of 3.029 Ω cm² at the interface between CE and PE. The excellent performance was observed in the fabricated DSSCs using PVA (85%)/PPy (10%)/KI (5%)/I₂ polymer electrolyte with a short-circuit current density of 11.071 mA cm^?2, open-circuit voltage of 0.644 V, fill factor of 0.575, and photovoltaic conversion efficiency of 4.09% under the light intensity of 100 mW cm^?2. Hence, the PPy content in polymer electrolyte influences the remarkable performance of low-cost DSSC.     

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.     

Efficiency enhancement with chloride to iodide ion exchange of benzimidazolium salt as a redox mediator

The new benzimidazolium derivative (SM-1) salt with ion exchange from the (SM-0) was fabricated and characterized by proton-nuclear magnetic resonance (¹H-NMR), carbon-nuclear magnetic resonance (¹³C-NMR), Fourier-transform infrared spectroscopy (FT-IR), electrospray ionization (EIS-MS), thermal analysis (TG), cyclic voltammetry (CV), and ultraviolet-visible spectroscopy (UV-vis), for electrolytes (liquid or dried) in the DSSC charge transportation mechanism. Also, the influence of ion exchange from chloride to iodine in the synthesized electrolytes, compared to other electrolytes (conventional or commercial), was investigated about DSSC performance efficiency. When using as a liquid electrolyte (SM-1), the power conversion efficiency (ƞ) of the working DSSC device was recorded as 1.980% and it was observed that the performances of DSSCs increased up to 56% when comparing dried electrolyte for SM-1 without conventional redox material (I^-/I₃^-). In the future, different molecular modifications of this type of benzimidazole derivatives or mixtures with conventional redox couples may further improve the performance of DSSC devices.     

Self-Assembled Graphene/MWCNT Bilayers as Platinum-Free Counter Electrode in Dye-Sensitized Solar Cells

We describe the preparation and properties of bilayers of graphene- and multi-walled carbon nanotubes (MWCNTs) as an alternative to conventionally used platinum-based counter electrode for dye-sensitized solar cells (DSSC). The counter electrodes were prepared by a simple and easy-to-implement double self-assembly process. The preparation allows for controlling the surface roughness of electrode in a layer-by-layer deposition. Annealing under N₂ atmosphere improves the electrode's conductivity and the catalytic activity of graphene and MWCNTs to reduce the I₃⁻ species within the electrolyte of the DSSC. The performance of different counter-electrodes is compared for ZnO photoanode-based DSSCs. Bilayer electrodes show higher power conversion efficiencies than monolayer graphene electrodes or monolayer MWCNTs electrodes. The bilayer graphene (bottom)/MWCNTs (top) counter electrode-based DSSC exhibits a maximum power conversion efficiency of 4.1 % exceeding the efficiency of a reference DSSC with a thin film platinum counter electrode (efficiency of 3.4 %). In addition, the double self-assembled counter electrodes are mechanically stable, which enables their recycling for DSSCs fabrication without significant loss of the solar cell performance.     

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.     

Efficient Counter Electrode Manufactured from Ag2S Nanocrystal Ink for Dye‐Sensitized Solar Cells

It is generally believed that silver or silver‐based compounds are not suitable counter electrode (CE) materials for dye‐sensitized solar cells (DSSCs) due to the corrosion of the I^?/I₃^? redox couple in electrolytes. However, Ag₂S has potential applications in DSSCs for catalyzing I₃^? reduction reactions because of its high carrier concentration and tiny solubility product constant. In the present work, CE manufactured from Ag₂S nanocrystals ink exhibited efficient electrocatalytic activity in the reduction of I₃^? to I^? in DSSCs. The DSSC consisting of Ag₂S CE displayed a higher power conversion efficiency of 8.40 % than that of Pt CE (8.11 %). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiated stability. The simple composition, easy preparation, stable chemical property, and good catalytic performance make the developed Ag₂S CE as a promising alternative to Pt CE in DSSCs.     

Effect of organic dye on the performance of dye-sensitized solar cell utilizing TiO2 nanostructure films synthesized via CTAB-assisted liquid phase deposition technique

This work is concerned with the growth of TiO₂ nanostructures as photovoltaic materials of dyesensitized solar cell (DSSC) via phase liquid deposition technique treated with CTAB surfactant. This work investigates the influence of organic dyes, N719, N3 and Z907 as photosensitizer on the photovoltaic parameters of TiO₂ nanostructures dye-sensitized solar cells (DSSCs). It also highlights the effect of the concentration of the best dye, N719 on the performance of the cell. The platinum films as counter electrode of the DSSC were prepared by sputtering platinum pellet on ITO substrate. The redox couple of the electrolyte utilized in the DSSC was iodide/triiodide. The cell sensitized with N719 dye demonstrated the best performance compared with the cell sensitized with another two dyes, N3 and Z907. This is due to N719 dye possess the highest optical absorption in visible region. The cell sensitized with 0.8 mM N719 dye performs the highest short-circuit current density, J _sc and power conversion efficiency, η since it posses the highest absorption in visible region. The DSSC utilizing 0.8 mM N719 dye demonstrated the highest J _sc and η of 6.48 mA cm^?2 and 1.69%, respectively.     

LiTFSI as a plastic salt in the quasi-solid state polymer electrolyte for dye-sensitized solar cells

Ionic conductivity and the type of ions are important for the composite polymer electrolyte (CPE) of the dye-sensitized solar cells (DSSCs). Lithium bis(trifluoromethane sulphone)imide (LiTFSI for short) which is easy to dissociate, is added in the composite polymer electrolyte(CPE) as a plasticizer. The LiTFSI acts differently from the conventional LiClO₄. LiTFSI changes the conformation of the polymer chain and shows higher ionic conductivity than LiClO₄. That contributes to the improvement of the short current density of the DSSC. Furthermore, the DSSCs with LiTFSI modification show higher photovoltage than the LiClO₄. The anions of TFSI^? prohibit the interface recombination more effectively compared with the LiClO₄ as the electrochemical impedance spectroscopy indicated. With the LiTFSI modified electrolyte, the performances of the DSSCs under 1 Sun, AM1.5 are improved and reaches the highest of 4.82% at the LiTFSI:LiI = 0.116:1, much better than the original DSSC(3.6%) and the LiClO₄ modified CPE electrolyte DSSC(4.32%).     

Quantum dot doped solid polymer electrolyte for device application

ZnS capped CdSe quantum dots embedded in PEO:KI:I₂ polymer electrolyte matrix have been synthesized and characterized for dye sensitized solar cell (DSSC) application. The complex impedance spectroscopy shows enhance in ionic conductivity (σ) due to charges provide by quantum dots (QD) while AFM affirm the uniform distribution of QD into polymer electrolyte matrix. Cyclic voltammetry revealed the possible interaction between polymer electrolyte, QD and iodide/iodine. The photovoltaic performances of the DSSC containing quantum dots doped polymer electrolyte was also found to improve.     

Quasi-solid-state dye-sensitized solar cells assembled by in-situ chemical cross-linking at ambient temperature

Cross-linked gel polymer electrolytes containing aluminum oxide nanoparticles are successfully prepared using in-situ chemical cross-linking at room temperature after injection of the gel precursor into a dye-sensitized solar cell (DSSC). This makes it possible to directly solidify the electrolyte in the cell without leakage of solvent and to maintain close interfacial contact with the porous TiO₂ electrode. The quasi-solid-state DSSC assembled with gel polymer electrolyte containing 20 wt.% Al₂O₃ particles yields an overall conversion efficiency of 5.25% under AM 1.5 illumination at 100 mW cm^{− 2}.     

Polyethyleneoxide (PEO)-based, anion conducting solid polymer electrolyte for PEC solar cells

Solid polymer electrolyte membranes were prepared by complexing tetrapropylammoniumiodide (Pr₄N⁺I^?) salt with polyethylene oxide (PEO) plasticized with ethylene carbonate (EC), and these were used in photoelectrochemical (PEC) solar cells fabricated with the configuration glass/FTO/TiO₂/dye/electrolyte/Pt/FTO/glass. The PEO/Pr₄N⁺I^?+I₂?=?9:1 ratio gave the best room temperature conductivity for the electrolyte. For this composition, the plasticizer EC was added to increase the conductivity, and a further conductivity enhancement of four orders of magnitude was observed. An abrupt increase in conductivity occurs around 60–70 wt% EC; the room temperature conductivity was 5.4?×?10^?7 S cm^?1 for 60 wt% EC and 4.9?×?10^?5 S cm^?1 for the 70 wt% EC. For solar cells with electrolytes containing PEO/Pr₄N⁺I^?+I₂?=?9:1 and EC, IV curves and photocurrent action spectra were obtained. The photocurrent also increased with increasing amounts of EC, up to three orders of magnitude. However, the energy conversion efficiency of this cell was rather low.     

Growth of aligned polypyrrole acicular nanorods and their application as Pt‐free semitransparent counter electrode in dye‐sensitized solar cell

Polypyrrole films on fluorine doped tin oxide (FTO)‐coated glass substrate were prepared in situ by placing FTO/glass substrates where pyrrole was polymerized by methyl orange‐ferric chloride complex. The atomic force microscopy image indicated growth of acicular nanorods of polypyrrole. These films exhibited catalytic activity towards I₃⁻/I⁻ redox couple and have been investigated for counter electrode application in dye‐sensitized solar cell (DSSC). The fabricated DSSC with N719 dye/TiO₂ as photoanode, and PPy/FTO as counter electrode shows ~1.7% efficiency.     

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.     

High performance dye-sensitized solar cell based on 2-mercaptobenzimidazole doped poly(vinylidinefluoride-co-hexafluoropropylene) based polymer electrolyte

In this work, the influence of 2-mercaptobenzimidazole (2-MCBI) on poly(vinylidinefluoride-co-hexafluoropropylene)/KI/I₂ (PVDF-HFP/KI/I₂) polymer electrolytes were studied. The pure and different weight percentage ratios (20, 30, 40 and 50%) of 2-MCBI doped PVDF-HFP/KI/I₂ electrolytes were prepared by a solution casting technique. The as-prepared polymer electrolyte films were characterized using various techniques such as Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffractometer (XRD), alternating current (AC)-impedance analysis. The addition of 2-MCBI with pure PVDF-HFP/KI/I₂ was found to increase the ionic conductivity of electrolyte. Among the various additions, 30 wt% 2-MCBI doped PVDF-HFP/KI/I₂ showed the highest room temperature ionic conductivity values than the others. The dye-sensitized solar cell (DSSC) fabricated using this optimized polymer electrolyte achieved a high power conversion efficiency of 4.40% than the pure PVDF-HFP/KI/I₂ (1.74%) at similar experimental conditions. Thus, the 2-MCBI doped polymer electrolyte has proven to be an effective substitute to the liquid electrolyte in DSSCs.     

Optically Transparent Gold Nanoparticles for DSSC Counter-Electrode: An Electrochemical Characterization

A gold nanoparticles transparent electrode was realized by chemical reduction. This work aims to compare the transparent gold nanoparticles electrode with a more commonly utilized gold-film-coated electrode in order to investigate its potential use as counter-electrode (CE) in dye-sensitized solar cells (DSSCs). A series of DSSC devices, utilizing I⁻/I³⁻ and Co(III)/(II) polypyridine redox mediators [Co(dtb)3]³⁺/²⁺; dtb = 4,4′ditert-butyl-2,2′-bipyridine)], were evaluated. The investigation focused firstly on the structural characterization of the deposited gold layers and then on the electrochemical study. The novelty of the work is the realization of a gold nanoparticles CE that reached 80% of average visible transmittance. We finally examined the performance of the transparent gold nanoparticles CE in DSSC devices. A maximum power conversion efficiency (PCE) of 4.56% was obtained with a commercial I⁻/I³⁻-based electrolyte, while a maximum 3.1% of PCE was obtained with the homemade Co-based electrolyte.