Xiaojian Chen

Bis-imidazolium based poly(ionic liquid) electrolytes for quasi-solid-state dye-sensitized solar cells

Bis-imidazolium based poly(ionic liquid), poly(1-butyl-3-(1-vinylimidazolium-3-hexyl)-imidazolium bis(trifluoromethanesulfonyl)imide) (Poly[BVIm][HIm][TFSI]) and mono-imidazolium based poly(ionic liquid), poly(1-butyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide) (Poly[BVIm][TFSI]), were synthesized and dissolved in room temperature ionic liquids (ILs) to form quasi-solid-state electrolytes for dye-sensitized solar cells (DSSCs), without using any volatile organic solvent. Compared with mono-imidazolium based poly[BVIm][TFSI], bis-imidazolium based poly[BVIm][HIm][TFSI] electrolytes showed a higher thermal stability and conductivity due to the charge transport networks formed in the gel electrolytes via the π–π stacked imidazolium rings. The DSSCs based on the poly[BVIm][HIm][TFSI] gel electrolyte showed a superior long-term stability and yielded a power conversion efficiency of 5.92% under the simulated air mass 1.5 solar spectrum illumination at 100 mW cm−2. This study offered a feasible method to fabricate quasi-solid-state DSSCs in future practical applications.

High-Temperature Solid-State Dye-Sensitized Solar Cells Based on Organic Ionic Plastic Crystal Electrolytes

Organic ionic plastic crystal, 1-ethyl-1-methyl pyrrolidinium iodide (P(12) I), is employed as the solid-state electrolytes for dye-sensitized solar cells. The fabricated solid-state devices show an overall power conversion efficiency of ~5.8% under AM 1.5 radiation (50 mW/cm(2) ) and excellent long-term stability at 80 °C.

Organic ionic plastic crystal-based electrolytes for solid-state dye-sensitized solar cells

An organic ionic plastic crystal, 1-ethyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (P12TFSI), was synthesized and doped with a room temperature ionic liquid, 1-propyl-3-methylimidazolium iodide (PMII). The prepared PMII/P12TFSI solid-state electrolytes were employed for dye-sensitized solar cells (DSSCs), without using any volatile organic solvent. The fabricated solid-state DSSCs yielded a power conversion efficiency of 5.12% under simulated air mass 1.5 solar spectrum illuminations at 50 mW cm−2. The superior long-term stability of the fabricated solid-state DSSCs indicated that the synthesized PMII/P12TFSI solid-state electrolytes could overcome the drawbacks of cells containing volatile solvents.

Water‐Resistant, Solid‐State, Dye‐Sensitized Solar Cells Based on Hydrophobic Organic Ionic Plastic Crystal Electrolytes

Water-resistant, solid-state, dye-sensitized solar cells with excellent long-term stability at 100% relative humidity and at 50 °C are fabricated on the basis of a novel hydrophobic organic ionic plastic crystal electrolyte and hybrid redox couple.

High performance all-solid-state dye-sensitized solar cells based on cyanobiphenyl-functionalized imidazolium-type ionic crystals

Organic ionic crystals carrying 4-cyano-4′-hydroxybiphenyl and imidazolium units were synthesized and applied as the electrolytes for dye-sensitized solar cells (DSSCs). The fabricated all-solid-state DSSCs achieved a cell efficiency of ∼5.11% at 55 °C under the simulated air mass 1.5 solar spectrum illuminations at 100 mW cm−2 because of the enhanced light harvesting capability of the electrolyte. To further improve the cell efficiency, 1-propyl-3-methylimidazolium iodine (PMII), was added into the electrolytes as a crystal growth inhibitor. These fabricated devices showed an enhanced power conversion efficiency (PCE) of ∼6.55% at 45 °C under the simulated air mass 1.5 solar spectrum illuminations at 50 mW cm−2, and a superior long-term stability. The cyanobiphenyl-functionalized ionic crystal based electrolytes have expanded our vision to explore new types of all-solid-state electrolytes for high-efficiency DSSCs.

Imidazolium functionalized cobalt tris(bipyridyl) complex redox shuttles for high efficiency ionic liquid electrolyte dye-sensitized solar cells

CoII/III redox couples and their derivatives have been extensively studied and applied as redox mediators for high efficiency organic solvent DSSCs. However, CoII/III complex redox mediator-based ionic liquid electrolyte DSSCs have not been studied so far due to the poor solubility of most CoII/III complexes in ionic liquid electrolytes. Herein, an imidazolium functionalized cobalt tris(bipyridyl) complex redox mediator ([Co((MeIm-Bpy)PF6)3]2+/3+) (((MeIm-Bpy)PF6)3 = 3,3′-(2,2′-bipyridine-4,4′-diyl-bis(methylene))bis(1-methyl-1H-imidazol-3-ium)hexafluorohosphate) with high redox potential and good solubility in ionic liquid electrolyte has been synthesized and applied in ionic liquid electrolyte DSSCs. Using the dye N719 as the photosensitizer, overall power conversion efficiencies of 7.37% and 8.29% are achieved in binary ionic liquid-based electrolyte under 1.5 solar spectrum illumination at 100 and 50 mW cm−2, respectively. Both values are considerably higher than those of the I−/I3− redox couple-based ionic liquid electrolyte.

Efficient light-scattering functionalized TiO2 photoanodes modified with cyanobiphenyl-based benzimidazole for dye-sensitized solar cells with additive-free electrolytes

Light-scattering functionalized cyanobiphenyl-based benzimidazole was synthesized and applied in the surface modification of dyed TiO2 photoanodes for dye-sensitized solar cells (DSSCs). DSSCs based on the ionic liquid and all-solid-state electrolytes were fabricated and characterized, without the addition of additives in the electrolytes. Compared with electrolytes containing the additive N-butylbenzimidazole (NBB), surface modification of dyed TiO2 photoanodes with cyanobiphenyl-based benzimidazole could enhance the values of the open-circuit photovoltage (Voc), short-circuit photocurrent density (Jsc) and the overall PCE of the fabricated DSSCs, due to the suppressed charge recombination rate, the conductivity optimization of the electrolytes and enhanced light harvesting capability at the TiO2 photoanode/electrolyte interface. Under the simulated air mass 1.5 solar spectrum illuminations at 100 mW cm−2, the fabricated devices achieved a cell efficiency of ∼6.63% and ∼5.82% for ionic liquid and all-solid-state electrolytes, respectively. These results provide an alternative strategy for high performance DSSCs with additive-free electrolytes.

Imidazolium functionalized TEMPO/iodide hybrid redox couple for highly efficient dye-sensitized solar cells

The imidazolium functionalized stable organic radical 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO), and 1-methyl-3-(2-oxo-2-(2,2,6,6-tetramethyl-1-oxyl-4-piperidoxyl) butyl)imidazolium bis(trifluoromethanesulfonyl) imide ([MeIm-TEMPO][TFSI]), were synthesized and characterized. The prepared [MeIm-TEMPO][TFSI]/1-propyl-3-methylimidazolium iodide (PMII) hybrid redox couple showed negligible absorption in the visible region and higher redox potential as compared with the iodide/triiodide (I−/I3−) redox couple. The resulting dye-sensitized solar cells (DSSCs) containing the imidazolium functionalized TEMPO/PMII hybrid redox couple in combination with organic dye (D205) exhibited average overall power conversion efficiencies of 8.2% and 9.1% under simulated air mass 1.5 solar spectrum illumination at 100 mW cm−2 and 50 mW cm−2, respectively, which are higher than that of the traditional PMII/I2 based electrolyte, probably due to the enhancement of the Voc and Jsc values of the hybrid electrolytes.

Silica nanoparticle doped organic ionic plastic crystal electrolytes for highly efficient solid-state dye-sensitized solar cells.

Organic ionic plastic crystal, 1-propyl-1-methylpyrrolidinium iodide (P₁₃I), which possesses a broad plastic phase from -36 to 135 °C, was doped with silica nanoparticles (SiO₂ NPs) and 1-ethyl-3-methylimidazolium iodide (EMII), for the preparation of SiO₂/EMII/P₁₃I solid-state electrolytes for dye-sensitized solar cells (DSSCs). The thermal properties of all the electrolytes, including solid-solid phase transitions and melting temperatures, were investigated by differential scanning calorimetry (DSC). The effect of silica particles on the ionic conductivity, diffusion of I⁻/I₃⁻ redox couple in electrolytes, and photovoltaic performance for solid-state DSSCs were investigated. The fabricated solid-state DSSCs yielded a high power conversion efficiency of 5.25% under simulated air mass 1.5 solar spectrum illuminations at 50 mW cm⁻². Furthermore, the DSSCs based on SiO₂/EMII/P₁₃I solid-state electrolytes show good stability after an accelerating aging test, demonstrating potential practical applications.