Microstructural Development and Rheological Study of a Nanocomposite Gel Polymer Electrolyte Based on Functionalized Graphene for Dye-Sensitized Solar Cells

For a liquid electrolyte-based dye-sensitized solar cell (DSSC), long-term device instability is known to negatively affect the ionic conductivity and cell performance. These issues can be resolved by using the so called quasi-solid-state electrolytes. Despite the enhanced ionic conductivity of graphene nanoplatelets (GNPs), their inherent tendency toward aggregation has limited their application in quasi-solid-state electrolytes. In the present study, the GNPs were chemically modified by polyethylene glycol (PEG) through amidation reaction to obtain a dispersible nanostructure in a poly(vinylidene fluoride-co-hexafluoro propylene) copolymer and polyethylene oxide (PVDF–HFP/PEO) polymer-blended gel electrolyte. Maximum ionic conductivity (4.11 × 10⁻³ S cm⁻¹) was obtained with the optimal nanocomposite gel polymer electrolyte (GPE) containing 0.75 wt% functionalized graphene nanoplatelets (FGNPs), corresponding to a power conversion efficiency of 5.45%, which was 1.42% and 0.67% higher than those of the nanoparticle-free and optimized-GPE (containing 1 wt% GNP) DSSCs, respectively. Incorporating an optimum dosage of FGNP, a homogenous particle network was fabricated that could effectively mobilize the redox-active species in the amorphous region of the matrix. Surface morphology assessments were further performed through scanning electron microscopy (SEM). The results of rheological measurements revealed the plasticizing effect of the ionic liquid (IL), offering a proper insight into the polymer–particle interactions within the polymeric nanocomposite. Based on differential scanning calorimetry (DSC) investigations, the decrease in the glass transition temperature (and the resultant increase in flexibility) highlighted the influence of IL and polymer–nanoparticle interactions. The obtained results shed light on the effectiveness of the FGNPs for the DSSCs.

Poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) and polyvinylidene fluoride blend doped with oxydianiline-based thiourea derivatives as a novel and modest gel electrolyte system for dye-sensitized solar cell applications

Unique symmetrical thiourea derivatives with an oxydianiline core were synthesized using cost-effective and simple methods. A new gel electrolyte system was prepared using these thiourea additives along with a highly conductive PEG–PPG–PEG block copolymer, PVDF, and an iodide/triiodide redox couple. The PEG units present in the electrolyte are well-known for their intense segmental motion of ions, which can degrade the recombination rate and favour the charge transfer. The thiourea additives interacted well with the redox couple to limit iodine sublimation and their adsorption induced a negative potential shift for TiO₂. The highest efficiency attained by utilizing such gel polymer electrolytes was 5.75%, especially with 1,1′-(oxybis(4,1-phenylene))bis(3-(6-methylpyridin-2-yl) thiourea) (OPPT), under an irradiation of 100 mW cm⁻². The electrochemical impedance spectroscopy, UV-vis absorption spectroscopy, differential scanning calorimetry, and FTIR spectroscopy data of such gel polymer electrolytes favoured the PCE order of the additives used in DSSCs. The improvement in the DSSC performance with symmetrical thioureas having electron-rich atoms was practically attributed to the reduction of back electron transfer, dye regeneration, and hole transport.

A unique gel polymer electrolyte was prepared using PVDF and PEG–PPG–PEG block copolymer with I⁻/I₃⁻ for DSSC application. This is a cost-effective method used for the synthesis of thiourea additives. The GPE with OPPT thiourea additive achieved a good efficiency of 5.7%.

Nanostructured polymers with embedded self-assembled networks: reversibly tunable phase behaviors and physical properties

1,3:2,4-Dibenzylidene sorbitol (DBS) can self-assemble into nanofibrillar networks to form organogels in a variety of organic solvents and liquid polymers. In this study, we induced the formation of organogels in solid poly(ethylene glycol) (PEG) polymers. The DBS gels appeared at temperatures above the melting point of PEG. When the DBS/PEG systems were heated at higher temperatures, they exhibited transparent, clear solution states due to the collapse of the DBS networks. Upon cooling to room temperature, the DBS self-assembled nanostructures appeared again, followed by the solidification (crystallization) of PEG. These DBS/PEG systems possess three different phases (solid, gel and liquid) and can be tuned by changes in the composition and temperature. Using polarized optical microscopy, all the gel systems were found to exhibit spherulite-like morphologies. Small-angle X-ray scattering results revealed lamellar packing in these spherulite-like morphologies. Transmission electron microscopy verified that these features were formed due to the presence of DBS nanofibrillar networks consisting of fibrils that were approximately 10-20 nm in diameter. In addition, the crystallization of PEG was strongly templated by the existing DBS nanofibrils. Moreover, there were no significant distortions in the PEG crystal structures due to the confinement of PEG between the DBS nanofibrils.

Self-assembly behaviors of dibenzylidene sorbitol hybrid organogels with inorganic silica

Molecular interactions, rheological behaviors and microstructures of 1,3:2,4-dibenzylidene-d-sorbitol (DBS)/poly(ethylene glycol) (PEG) organogel-inorganic silica hybrid materials are discussed in this study. DBS can dissolve in low-molecular-weight PEG to form organogels. The self-assembly behavior of these organogels was significantly influenced by the addition of the inorganic silica. The π interactions between the phenyl rings of DBS were not influenced by silica addition; however, the addition of silica affected the intermolecular hydrogen bonding of DBS, which interacts with PEG. The silica more likely interacted with PEG and decreased the intermolecular interactions between DBS and PEG, which resulted in an increase in the self-assembly of DBS. Therefore, the gel formation time and gel dissolution temperature increased as the amount of silica increased, as determined by dynamic rheological instruments. In addition, these organogel systems were all found to exhibit spherulite-like textures under polarized optical microscopy. The addition of silica and the increased DBS self-assembly in PEG resulted in a higher self-assembly temperature of the organogels. The higher temperature resulted in the presence of fewer nucleation sites and larger spherulite sizes in these systems. Small-angle X-ray scattering results demonstrated lamellar packing in these spherulite-like morphologies. Furthermore, the organogels with silica affected the intermolecular hydrogen bonding between DBS and PEG to facilitate the self-assembly of DBS, which resulted in increased diameter sizes of the DBS nanofibrils, as observed using scanning electron microscopy. It was observed that the silica was entrapped within these nanofibrillar networks.

Three-dimensional graphene networks and reduced graphene oxide nanosheets co-modified dye-sensitized solar cells

Graphene assisted dye-sensitized solar cells (DSSCs) have drawn increasing attention because of their high performances.

Efficient quasi-solid state dye sensitized solar cell using succinonitrile : thiourea based electrolyte composition

SEM micrograph of the optimized electrolyte with SCN : TU. Inset shows the current density–voltage characteristics of the DSSCs with reference and optimized electrolytes, A1 and A2, respectively.