Influence of solvent on the poly (acrylic acid)-oligo-(ethylene glycol) polymer gel electrolyte and the performance of quasi-solid-state dye-sensitized solar cells

The influence of solvents on the property of poly (acrylic acid)-oligo-(ethylene glycol) polymer gel electrolyte and photovoltaic performance of quasi-solid-state dye-sensitized solar cells (DSSCs) were investigated. Solvents or mixed solvents with large donor number enhance the liquid electrolyte absorbency, which further influences the ionic conductivity of polymer gel electrolyte. A polymer gel electrolyte with ionic conductivity of 4.45 mS cm⁻¹ was obtained by using poly (acrylic acid)-oligo-(ethylene glycol) as polymer matrix, and absorbing 30 vol.% N-methyl pyrrolidone and 70 vol.% γ-butyrolactone with 0.5 M NaI and 0.05 M I₂. By using this polymer gel electrolyte coupling with 0.4 M pyridine additive, a quasi-solid-state dye-sensitized solar cell with conversion efficiency of 4.74% was obtained under irradiation of 100 mW cm⁻² (AM 1.5).     

Influence of molecular weight of PEG on the property of polymer gel electrolyte and performance of quasi-solid-state dye-sensitized solar cells

A new kind of polymer gel electrolyte based on poly(acrylic acid)-poly(ethylene glycol) (PAA-PEG) hybrid was synthesized. The factor of molecular weight of PEG in the hybrid plays an important role in determining the liquid electrolyte absorbency of the hybrid and ionic conductivity of the polymer gel electrolyte, sequentially affects the photovoltaic performance of quasi-solid-state dye-sensitized solar cells. Using the hybrid with PEG molecular weight of 20,000, a polymer gel electrolyte with liquid electrolyte absorbency of 6.9 g g⁻¹ and ionic conductivity of 5.35 mS cm⁻¹ was obtained. Based on the polymer gel electrolyte, a quasi-solid-state dye-sensitized solar cell with conversion efficiency of 5.25% was achieved under irradiation of AM 1.5, 100 mW cm⁻².     

Application of poly(acrylic acid-g-gelatin)/polypyrrole gel electrolyte in flexible quasi-solid-state dye-sensitized solar cell

A novel gel polymer electrolyte based on poly(acrylic acid-g-gelatin)/polypyrrole with conductivity of 14.1 mS cm⁻¹ was prepared. Based on the gel electrolyte, a flexible quasi-solid-state dye-sensitized solar cell was fabricated by using a low-temperature filming technique. Owing to high conductivity and the catalytic function of polypyrrole for I⁻/I₃⁻ redox reaction for the gel electrolyte, the flexible quasi-solid-state dye-sensitized solar cell showed a light-to-electric energy conversion efficiency of 1.28%, under a simulated solar light irradiation with intensity of 100 mW cm⁻² (AM 1.5).     

A polyblend electrolyte (PVP/PEG+KI+I2) for dye-sensitized nanocrystalline TiO2 solar cells

A novel polyblend electrolyte consisting of KI and I₂ dissolved in a blending polymer of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) was prepared. The formation of ⁻I₃ in the polymer electrolyte was confirmed by X-ray photoelectron spectroscopy (XPS) characterization. Due to the coordinating and plasticizing effect by PVP, the ionic conductivity of the polyblend electrolyte is enhanced. The highest ionic conductivity of 1.85 mS cm⁻¹ for the polyblend electrolyte was achieved by optimizing the compositions as 40 wt.% PVP + 60 wt.% PEG + 0.05 mmol g⁻¹ I₂ + 0.10 mmol g⁻¹ KI. Based on the polyblend electrolyte, a DSSC with fill factor of 0.59, short-circuit density of 9.77 mA cm⁻², open-circuit voltage of 698 mV and light-to-electricity conversion efficiency of 4.01% was obtained under AM 1.5 irradiation (100 mW cm⁻²).     

The application of P(MMA-co-MAA)/PEG polyblend gel electrolyte in quasi-solid state dye-sensitized solar cell at higher temperature

A poly(methyl methacrylate-co-methacrylate acid)/poly(ethylene glycol) [P(MMA-co-MAA)/PEG] polyblend with viscoelasticity was synthesized by a copolymerizing reaction between methyl methacrylate (MMA) and methacrylate acid (MAA) using azobisisobutyronitrile (AIBN) as initiator in poly(ethylene glycol) (PEG) methanol solution. Then, a polyblend gel electrolyte was prepared by adding KI and I₂ to P(MMA-co-MAA)/PEG system. The influence of compositions of the polyblend gel electrolyte on the ionic conductivity and the effect of temperature on photoelectronic performance of quasi-solid state dye-sensitized solar cell (QS-DSSC) were discussed. It was found that the polyblend gel electrolyte was a good candidate as high-temperature electrolyte for QS-DSSCs. Under an optimized condition, the highest conductivity of the polyblend gel electrolyte was 2.70 mS/cm² at 30 °C. Based on the polyblend gel electrolyte, a light-to-electricity conversion efficiency of 4.85% for QS-DSSC was achieved under AM 1.5 simulated solar light illumination at 60 °C.     

The role of gel electrolyte composition in the kinetics and performance of dye-sensitized solar cells

Gel-type polymer electrolytes based on the copolymer poly(ethylene oxide-co-epichlorohydrin) and the plasticizer γ-butyrolactone (GBL) were optimized and applied in dye-sensitized solar cells. The plasticizer added to the electrolyte allowed the dissolution of a higher concentration of salt, reaching conductivity values close to 1 mS cm⁻¹ for the sample prepared with 30 wt% of LiI. Raman spectroscopy confirmed polyiodide formation in the electrolyte when the salt concentration exceeds 7.5 wt%, introducing a significant contribution of electronic conductivity in the electrolyte. The devices were characterized under AM 1.5 conditions and the I-V curves were fitted using a two diode equation. Increasing the concentration of LiI-I₂ accelerates dye cation regeneration as measured by transient absorption spectroscopy; however, it also contributes to an increase in the dark current of the cell by one order of magnitude. The best performance was achieved for the solar cell prepared with the electrolyte containing 20 wt% of LiI, with efficiencies of 3.26% and 3.49% at 100 and 10 mW cm⁻² of irradiation, respectively.     

Studies on isomeric effects of 2- and 4-Mercapto pyridine as dopants in polymer electrolyte in dye-sensitized solar cells

In this present work, isomers like 2- and 4-Mercapto pyridine were used as dopants (additives) in Poly (ethylene oxide) based polymer electrolyte and their effects in dye-sensitized solar cells (DSC) have been investigated. Due to the coordinating and plasticizing effects of Mercapto pyridine, enhanced ionic conductivity and reduced crystallinity of PEO polymer electrolyte accompanied by a better penetration of the same into the dye coated nanocrystalline TiO₂ in order to have better performances were achieved. The 2-Mercapto pyridine doped PEO (E) shows comparatively better performance than 4-Mercapto pyridine doped one (F), is due to the fact that the π-electron donicity of 2-Mercapto pyridine is greater. These results suggests that the electron donating capacity of 2-Mercapto pyridine and 4-Mercapto pyridine would influence the interaction of nanocrystalline TiO₂ electrode and I⁻/I₃⁻ redox couple leading to radical changes in the cell performance.     

Influences of poly(ether urethane) introduction on poly(ethylene oxide) based polymer electrolyte for solvent-free dye-sensitized solar cells

A poly(ether urethane) (PEUR)/poly(ethylene oxide) (PEO)/SiO₂ based nanocomposite polymer is prepared and employed in the construction of high efficiency all-solid-state dye-sensitized nanocrystalline solar cells. The introduction of low-molecular weight PEUR prepolymer into PEO electrolyte has greatly enhance the electrolyte performance by both improving the interfacial contact properties of electrode/electrolyte and decreasing the PEO crystallization, which were confirmed by XRD and SEM characteristics. The effects of polymer composition, nano SiO₂ content on the ionic conductivity and I₃⁻ ions diffusion of polymer-blend electrolyte are investigated. The optimized composition yields an energy conversion efficiency of 3.71% under irradiation by white light (100 mW cm⁻²).     

Influence of 2,6 (N-pyrazolyl)isonicotinic acid on the photovoltaic properties of a dye-sensitized solar cell fabricated using poly(vinylidene fluoride) blended with poly(ethylene oxide) polymer electrolyte

A novel method of introducing a synthesized organic nitrogenous compound 2,6 (N-pyrazolyl)isonicotinic acid (BNIN) and its effect on the conduction behavior of poly(vinylidene fluoride) (PVdF)–poly(ethylene oxide) (PEO) polymer-blend electrolyte with potassium iodide (KI) and iodine (I₂) and the corresponding performance of the dye-sensitized solar cells (DSSCs) were studied. A systematic investigation of the blends using FTIR provides evidence of interaction of BNIN with the polymer. Differential scanning calorimetry (DSC) study proves the miscibility of these polymers. Due to the coordinating and plasticizing effects of BNIN, the ionic conductivity of polymer blend electrolytes is enhanced. The efficiency of DSSC using BNIN doped polymer blend electrolyte was 7.3% under an illumination of 60 mW cm⁻² were observed for the best performance of a solar cell in this work.     

Fabrication of hole-patterned TiO2 photoelectrodes for solid-state dye-sensitized solar cells

We suggest a simple process to fabricate a hole-patterned TiO₂ electrode for a solid-state dye-sensitized solar cell (DSSC) to enhance cell performance through interfacial properties of the electrode with the electrolyte with minimum dye loading. The method involves prepatterning of SU-8 photoresist on a conducting glass, followed by the deposition of a nanocrystalline TiO₂ layer, calcination at 450 °C and characterization using scanning electron microscopy (SEM). Hole-patterned TiO₂ photoelectrodes yielded better solar energy conversion efficiency per dye loading compared to a conventional non-patterned photoelectrode. For example, a 50 μm hole-patterned DSSC exhibited 4.50% conversion efficiency in the solid state, which is comparable to an unpatterned flat TiO₂ photoelectrode (4.57%) however the efficiency per dye loading of the former (0.986%/g) was much greater than that of the latter (0.898%/g). The improvement was attributed to improved transmittance through the electrode as well as better interfacial properties between the electrolyte and electrode, as confirmed by UV-visible spectroscopy and electrochemical impedance (EIS) analysis.     

The use of poly(vinylpyridine-co-acrylonitrile) in polymer electrolytes for quasi-solid dye-sensitized solar cells

Poly(vinylpyridine-co-acrylonitrile) (P(VP-co-AN)) was used to form polymer electrolytes for dye-sensitized solar cells (DSSCs). The effects of P(VP-co-AN) on the photovoltaic performances of DSSCs have been investigated with nonaqueous electrolytes containing alkali-iodide and iodine. It was found that the effect of P(VP-co-AN) on V_oc closely related to its amount in the electrolyte. Lower amount of P(VP-co-AN) was benefit for the construction of a solar cell containing P(VP-co-AN) with higher energy conversion efficiency. Chemically crosslinking solidification with backbone polymer P(VP-co-AN) amount of 3% fabricated quasi-solid DSSCs with 10% increased conversion efficiencies with relative to that of the initial liquid DSSCs.     

Polymer electrolytes from PEO and novel quaternary ammonium iodides for dye-sensitized solar cells

Polymer electrolytes were prepared by blending high molecular weight poly(ethylene oxide) (PEO) and a series of novel quaternary ammonium iodides, the polysiloxanes with oligo(oxyethylene) side chains and quaternary ammonium groups. X-ray diffraction (XRD) measurements ensured relatively low crystallinity when the quaternary ammonium iodides were incorporated into the PEO host. The ionic conductivity of these complexes was improved with the addition of plasticizers. The improvement in the ionic conductivity was determined by the polarity, viscosity and amounts of plasticizers. A plasticized electrolyte containing the novel quaternary ammonium iodide was successfully used in fabricating a quasi-solid-state dye-sensitized solar cell for the first time. The fill factor and energy conversion efficiency of the cell were calculated to be 0.68 and 1.39%, respectively.     

Polyvinyl pyrrolidone aided preparation of TiO2 films used in flexible dye-sensitized solar cells

Polyvinyl pyrrolidone (PVP) is introduced to low temperature preparation of a good quality TiO₂ film used in flexible dye-sensitized solar cells (DSSCs). The samples are characterized by scanning electron microscopy and UV–vis absorption spectra, the photovoltaic performance of the DSSC is measured. It is found that PVP can improve the dispersion of TiO₂ particles and the adherence of TiO₂ particles to flexible substrate, as well as the adsorption of sensitized dye to TiO₂ film. Additionally, ultraviolet light irradiation can eliminate organics remained on the surface the TiO₂ film and improve the surface state of TiO₂ film. Under an optimal condition, a flexible DSSC using TiO₂ film doped PVP and UV irradiation treated achieves a light-to-electric energy conversion efficiency of 3.02% under irradiation with a simulate solar light intensity of 100 mW cm⁻².     

Characterization of poly(vinylidenefluoride-co-hexafluoropropylene)-based polymer electrolyte filled with TiO2 nanoparticles

Nanoscale TiO₂ particle filled poly(vinylidenefluoride-co-hexafluoropropylene) film is characterized by investigating some properties such as surface morphology, thermal and crystalline properties, swelling behavior after absorbing electrolyte solution, chemical and electrochemical stabilities, ionic conductivity, and compatibility with lithium electrode. Decent self-supporting polymer electrolyte film can be obtained at the range of <50 wt% TiO₂. Different optimal TiO₂ contents showing maximum liquid uptake may exist by adopting other electrolyte solution. Room temperature ionic conductivity of the polymer electrolyte placed surely on the region of >10⁻³ S/cm, and thus the film is very applicable to rechargeable lithium batteries. An emphasis is also be paid on that much lower interfacial resistance between the polymer electrolyte and lithium metal electrode can be obtained by the solid-solvent role of nanoscale TiO₂ filler.     

Effect of Cr-doping on the physicochemical properties of blue TiO2 and its application in dye-sensitized solar cells via low-temperature fabrication process

Cr-doped blue TiO₂ (Cr-BTiO₂) nanoparticles were fabricated at room temperature using lithium-ethylenediamine (Li-EDA) as reducing agent. The addition of Li-EDA promotes the selective reduction of the rutile phase of TiO₂ into the amorphous phase keeping anatase phase unaltered. Hence, the phase-selective reduction of TiO₂ leads to the formation of blue TiO₂ nanoparticles. Synthesized samples were characterized by equipment fitted with modern technology. The shifting of (101) peak to a lower angle (2θ) in Cr-BTiO₂ in X-ray diffraction (XRD) pattern suggests the successful doping of chromium into TiO₂ lattices. In Raman spectra, the shifting of the active Eg peak of Cr-BTiO₂ nanoparticles to higher wavenumber also suggests the successful substitution of Ti by Cr. The blue TiO₂ and Cr-BTiO₂ show increased absorption of light in the visible region compared to TiO₂ (P25). The modified TiO₂ samples have improved electron-hole separation tendency as predicted by the photoluminescence spectra (PL). Also, doping of Cr- into TiO₂ lattice results the formation of oxygen vacancy as detected by X-ray photoelectron spectroscopy (XPS). Among all samples, Cr-BTiO₂ demonstrated improvement in J_sc and overall incident photon to current conversion efficiency. Therefore, the synthetic effect is thus responsible for the enhancement in efficiency of Cr-BTiO₂ towards the dye-sensitized solar cell (DSSC) by 2.5 and 1.5 times higher than the P25 and blue TiO₂, respectively.     

Improved photovoltage and performance by aminosilane-modified PEO/P(VDF-HFP) composite polymer electrolyte dye-sensitized solar cells

A PEO/P(VDF-HFP) composite polymer electrolyte was modified by different amounts of NH₂-end functional silane (3-amonopropyltriethoxysilane, APTS). Fourier transform infrared (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were carried out to examine the configuration changes of the polymer electrolyte. The newly formed Si-O-Si network and interactions influenced the ionic conductivity of the APTS-modified polymer electrolyte and also enhanced the connection of the polymer electrolyte with the electrodes of the dye sensitized solar cells (DSSCs). The cyclic voltammograms and electrochemical impedance measurements indicated that the APTS deprotonated the TiO₂ photoanode surface and negatively changed the Fermi energy level and the conduction band edge to the vacuum level. This effectively reduced the interface recombination in the DSSC and improved the open circuit voltage. With moderate APTS content (0.1 M) modification, the DSSC exhibited a 58 mV improvement of photovoltage and an improved performance of 5.08% compared with 3.74% of the original DSSC.     

Application of a polymer heterojunction in dye-sensitized solar cells

Using a blend heterojunction consisting of a C₆₀ derivative, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), and poly(3-hexylthiophene) (P3HT) as a charge carrier transfer medium to replace the I₃⁻/I⁻ redox electrolyte, a novel TiO₂/dye/PCBM/P3HT dye-sensitized solar cell was fabricated and characterized. It was found that the P3HT/PCBM heterojunction widened the incident light harvest range from ultraviolet to visible light, and improved the photoelectrical response of the dye-sensitized solar cell. We investigated the influence of the PCBM/P3HT ratio and barrier layer on the photoelectric performance of the solar cell and proposed optimized preparation conditions. The optimized solar cell with a barrier layer and PCBM/P3HT ratio of 1:2 had a short circuit current density of 5.52 mA cm⁻², an open circuit voltage of 0.87 V, a fill factor of 0.640 and a light-to-electric energy conversion efficiency of 3.09% under a simulated solar light irradiation of 100 mW cm⁻².     

Photovoltaic performance improvement of dye-sensitized solar cells based on tantalum-doped TiO2 thin films

Dye-sensitized solar cells based on a tantalum (Ta)-doped TiO₂ thin film prepared by the hydrothermal method show a photovoltaic efficiency of 8.18%, which is higher than that of the undoped TiO₂ thin film (7.40%). The Mott-Schottky plot indicates that the Ta-doped TiO₂ photoanode shifts the flat band potential positively and increases the electron density. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO₂. Furthermore, the increased electron density caused by the Ta-doped TiO₂ improves the fill factor of the solar cell. The increased electron density accelerates the transfer rate of electrons in the Ta-doped TiO₂ thin films by comparison to undoped films, which is confirmed by intensity-modulated photocurrent spectroscopy measurements.     

PEO-imidazole ionic liquid-based electrolyte and the influence of NMBI on dye-sensitized solar cells

1-Oligo(ethylene oxide)-3-methylimidazolium iodide (PEOMImI) was synthesized and applied to dye-sensitized solar cells (DSSCs) by blending it with different 1-alkyl-3-methylimidazolium iodides used as ionic liquid electrolytes. The 1-propyl-3-methylimidazolium iodide (PMII) blend enabled the DSSC to attain a higher solar energy conversion efficiency of 4.52% under a light intensity of 100 mW cm⁻². The addition of N-methylimidazole (NMBI) to the electrolytes increased the conversion efficiency as compared to DSSCs based on NMBI-free electrolytes. The addition of both 1-allyl-3-methylimidazolium iodide (AMII) and NMBI enabled DSSCs to reach their highest solar energy conversion efficiency of 6.14% under a light intensity of 100 mW cm⁻². The ionic conductivity and diffusion coefficient of the triiodide were found to be augmented dramatically after adding NMBI, which leads to an increase in the photocurrent density. The enhancement mechanism of NMBI in the electrolyte was investigated by Raman spectroscopy and differential scanning calorimetry, and it was mainly due to the enhancement of electron exchange in electrolytes.     

Influence of iodine concentration on the photoelectrochemical performance of dye-sensitized solar cells containing non-volatile electrolyte

The effect of iodine concentration in the electrolyte with non-volatile solvent of dye-sensitized solar cells (DSCs) on photovoltaic performance was studied. The electron transport and interfacial recombination kinetics were also systematically investigated by electron impedance spectroscopy (EIS). With the iodine concentration increased from 0.025 to 0.1 M, open-circuit voltage (V_oc) and photocurrent density (J_sc) decreased while fill factor (ff) increased significantly. The decline of the V_oc and J_sc was mainly ascribed to increased electron recombination with tri-iodide ions (I₃⁻). The increased fill factor was primarily brought by a decrease in the total resistance. From impedance spectra of the solar cells, it can be concluded that increasing the iodine concentration in electrolytes could decrease charge transfer resistance (R_ct) and the chemical capacitance (C_μ), increase the electron transport resistance (R_t), and hence decrease the electron lifetime (τ) and the effective diffusion coefficient (D_n) of electrons in the TiO₂ semiconductor. With optimum iodine concentration, device showed a photocurrent density of 16.19 mA cm⁻², an open-circuit voltage of 0.765 V, a fill factor of 0.66, and an overall photo-energy conversion efficiency of 8.15% at standard AM 1.5 simulated sunlight (100 mW cm⁻²).