Influence of polymer concentration and dyes on photovoltaic performance of dye-sensitized solar cell with P(VdF-HFP)-based gel polymer electrolyte

A series of gel polymer electrolytes (GPEs) is synthesized using Poly(vinylidenefluoride-hexafluoropropylene) P(VdF-HFP) as the host matrix and propylene carbonate (PC)–diethyl carbonate (DEC) as plasticizers to fabricate dye-sensitized solar cells. Equal amounts of PC and DEC are used to comprehend high dielectric constant and low viscosity of the electrolyte. The as-prepared GPEs are characterized by XRD, FTIR and SEM. Their thermal properties and ionic conductivities are investigated by TGA/DSC analyses and AC impedance measurements, respectively. The optimized gel polymer electrolyte gives a maximum ionic conductivity of 5.25 × 10⁻³ S cm⁻¹ at room temperature. The formation of porous structure in the electrolyte film supports the entrapment of large volumes of liquid electrolyte inside its cavities. The role of N3 and N719 dyes are also investigated for better photovoltaic performance of DSSC. The overall light-to-electrical-energy conversion efficiencies of 3.95% and 4.41% are obtained for N3 and N719 dyes, respectively, under 100 mW cm⁻² irradiation, which are comparable to those obtained from the corresponding liquid electrolyte cell.     

Low molecular mass organogelator based gel electrolyte gelated by a quaternary ammonium halide salt for quasi-solid-state dye-sensitized solar cells

Quasi-solid-state dye-sensitized solar cells (DSC) are fabricated using tetradodecylammonium bromide as a low molecular mass organogelator (LMOG) to form gel electrolyte with a high solution-to-gel transition temperature (T_SG) of 75 °C to hinder flow and volatilization of the liquid. The steady-state voltammograms reveal that the diffusion of the I₃⁻ and I⁻ in the gel electrolyte is hindered by the self-assembled network of the gel. An increased interfacial exchange current density (j₀) of 4.95 × 10⁻⁸ A cm⁻² and a decreased electron recombination lifetime (τ) of 117 ms reveal an increased electron recombination at the dyed TiO₂ photoelectrode/electrolyte interface in the DSC after gelation. The results of the accelerated aging tests show that the gel electrolyte based dye-sensitized solar cell can retain over 93% of its initial photoelectric conversion efficiency value after successive heating at 60 °C for 1000 h, and device degradation is negligible after one sun light soaking with UV cutoff filter for 1000 h.     

Novel thixotropic gel electrolytes based on dicationic bis-imidazolium salts for quasi-solid-state dye-sensitized solar cells

Novel thixotropic gel electrolytes have been successfully prepared by utilizing oligomeric poly(ethylene oxide) (PEO)-based bis-imidazolium diiodide salts and hydrophilic silica nanoparticles for application in quasi-solid-state dye-sensitized solar cells (DSSCs). The thixotropic gel-state of the ionic liquid-based composite electrolytes is confirmed by observing the typical hysteresis loop and temporary hydrogen bonding. On using the PEO-based composite electrolyte, a quasi-solid-state DSSC exhibited highly improved properties such as easy penetration of the electrolyte into the cell without leakage, long-term stability, high open-circuit voltage without the use of 4-tert-butylpyridine, and a high energy-conversion efficiency of 5.25% under AM 1.5 illumination (100 mW cm⁻²).     

Improved stability quasi-solid-state dye-sensitized solar cell based on polyether framework gel electrolytes

We report three improved stability dye-sensitized TiO₂ photoelectrochemical cells using quasi-solid polymer electrolytes containing poly(propylene oxide) (PPO), poly(ethylene oxide) (PEO) or poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (P₁₂₃). After introducing the polyether into the liquid electrolyte, the parameters of these quasi-solid-state solar cells are 90% comparable to that of the liquid photochemical cells, although the conductivities of these polyether framework gel electrolytes are lower than that of the bulk liquid electrolyte. The different morphologies of dried liquid electrolyte and the polyether gel electrolytes are characterized with an atomic force microscope (AFM) to explain the better stability exhibited by the polyether gel electrolytes.     

Al-doping driven electronic structure of α-NiS hollow spheres modified by rGO as high-rate electrode for quasi-solid-state capacitor

Developing an optimized electronic structure of α-NiS electrode material is critical for its high-rate electrochemical performance of quasi-solid-state capacitor. Herein, Al³⁺ have been doped into α-NiS lattice and the reduced graphene oxide (rGO) is employed to modify Al-doping α-NiS, to alleviate the low-mobility charge of α-NiS. The electronic structure and electrochemical properties of α-NiS hollow spheres induced by Al-doping and rGO modification are investigated, both experimental characterization and theoretical results confirm Al-doping affect the electronic structure and electrochemical performance of α-NiS hollow spheres. In the composite of Al-doping α-NiS and rGO (named as Al_xNi_1-xS/rGO), the doped heteroatom improves the intrinsic electronic structure of α-NiS and the rGO provides a good electric conducting network, leading to an enhanced electrochemical performance of α-NiS as high-rate electrode material. After evaluation, the optimized Al_0.2Ni_0.8S/rGO composite shows a superior reversible capacity of 1096 C g^?1 at 2 A g^?1, and retains a capability of 471 C g^?1 at a high-rate of 30 A g^?1. Moreover, an asymmetric quasi-solid-state hybrid capacitors assembled by Al_0.2Ni_0.8S/rGO and activated carbon presents a high energy density of 30.6 Wh kg^?1. This work provides a foundational strategy for the modification of α-NiS through Al-doping and combining with rGO, which has a positive effect on α-NiS electrode material in quasi-solid-state hybrid capacitors.     

Enhanced performance of a quasi-solid-state dye-sensitized solar cell with aluminum nitride in its gel polymer electrolyte

The effects of incorporation of aluminum nitride (AlN) in the gel polymer electrolyte (GPE) of a quasi-solid-state dye-sensitized solar cell (DSSC) were studied in terms of performance of the cell. The electrolyte, consisting of lithium iodide (LiI), iodine (I₂), and 4-tert-butylpyridine (TBP) in 3-methoxypropionitrile (MPN), was solidified with poly(vinyidene fluoride-co-hexafluoro propylene) (PVDF-HFP). The 0.05, 0.1, 0.3, and 0.5 wt% of AlN were added to the electrolyte for this study. XRD analysis showed a reduction of crystallinity in the polymer PVDF-HFP for all the additions of AlN. The DSSC fabricated with a GPE containing 0.1 wt% AlN showed a short-circuit current density (J_SC) and power-conversion efficiency (η) of 12.92±0.54 mA/cm² and 5.27±0.23%, respectively, at 100 mW/cm² illumination, in contrast to the corresponding values of 11.52±0.21 mA/cm² and 4.75±0.08% for a cell without AlN. The increases both in J_SC and in η of the promoted DSSC are attributed to the higher apparent diffusion coefficient of I⁻ in its electrolyte (3.52×10⁻⁶ cm²/s), compared to that in the electrolyte without AlN of a DSSC (2.97×10⁻⁶ cm²/s). At-rest stability of the quasi-solid-state DSSC with 0.1 wt% of AlN was found to decrease hardly by 5% and 7% at room temperature and at 40 °C, respectively, after 1000 h duration. The DSSC with a liquid electrolyte showed a decrease of about 40% at room temperature, while it virtually lost its performance in about 150 h at 40 °C. Explanations are further substantiated by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and by porosity measurements.     

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

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

Nanocomposite gel electrolyte with large enhanced charge transport properties of an I3/I redox couple for quasi-solid-state dye-sensitized solar cells

TiO₂ nanoparticles was introduced into quasi-solid-state Poly(vinylidenefluoride-co-hexafluoropropylene) (P(VDF-HFP)) based gel electrolyte to form nanocomposite gel electrolyte for quasi-solid-state dye-sensitized solar cells. The steady-state voltammograms revealed that the diffusion performance of the triiodide and iodide in the quasi-solid-state P(VDF-HFP) based gel electrolyte was greatly enhanced after the addition of TiO₂ nanoparticles. Especially, the apparent diffusion coefficient of I₃⁻ increased from 0.76×10⁻¹⁰ m²/s to 4.42×10⁻¹⁰ m²/s, reached the level of the liquid electrolyte (4.04×10⁻¹⁰ m²/s). By introducing TiO₂ nanoparticles, the photoelectric conversion efficiency of the gel based device increased from 5.72% to 7.18%, which reached the level of the liquid electrolytes based device (7.01%). The electrical impedance spectrum revealed that the addition of TiO₂ nanoparticles could reduce the charge recombination at the interface of dyed TiO₂ electrode/electrolyte. The results of the accelerated aging tests showed that the nano-TiO₂ composite gel electrolytes based devices could maintain 90% of their initial value after heating at 60 °C for 1000 h, which indicated that they had better thermostability than the corresponding normal gel electrolyte based devices and liquid electrolyte based devices.     

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).     

Liquid crystal based electrolyte with light trapping scheme for enhancing photovoltaic performance of quasi-solid-state dye-sensitized solar cells

In this study, nematic liquid crystal, 4-Cyano-4′-n-heptyloxybiphenyl, is introduced into the poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF) based polymeric gel electrolyte for quasi-solid-state dye-sensitized solar cells (DSC), aiming to improve the photovoltaic performance of DSC. The effects of liquid crystal on the electrochemical behavior of I₃⁻/I⁻ and photovoltaic performance, dynamic response as well as long-term stability of DSC are studied in detail. It is found that although the addition of liquid crystal would hinder the charge transport in the electrolyte, it could still fulfill the requirements of the photocurrent for DSC. More important, a significant increase in the photocurrent density for DSC is observed when liquid crystal is introduced into PVDF based polymeric gel electrolyte, resulting in the higher photoelectric conversion efficiency. The large increase in short-circuit photocurrent density could be attributed to the higher light harvesting efficiency, which is caused by the effective formation of light trapping scheme in electrolyte due to the addition of liquid crystal. Besides, at-rest long-term stability shows that when liquid crystal is introduced into PVDF based polymeric gel electrolyte, DSC could retain over 92% of its initial photoelectric conversion efficiency value after 1000 h, exhibiting relatively better stability.