Synthesis and characterization of cross-linkable ruthenium dye with ion coordinating property for dye-sensitized solar cells

Crosslinkable ruthenium complex dye, Ru(2,2′-bipyridine-4,4′-bicarboxylic acid)(4,4′-bis((4-vinyl benzyloxy)methyl)-2,2′-bipyridine)(NCS)₂ (denoted as Ru-S dye), was synthesized and characterized using ¹H-NMR, ¹³C-NMR, Fourier transform infrared (FTIR) and UV/vis spectroscopies.The power conversion efficiency of dye-sentitized solar cell (DSSC) using Ru-S and liquid electrolyte containing lithium iodide (LiI) reached 7.53% under standard global AM 1.5 full sunlight, which is partly attributed to Li⁺ being coordinated by Ru-S as verified by ATR-FTIR spectroscopy. As Ru-S was further crosslinked with glycerol propoxylate triacrylate (GPTA), not only 89% of dye retained on TiO₂ mesoporous surface after rinsed by 0.1 N NaOH aqueous solution, the power efficiency was also increased to 7.88%. As poly(methyl acrylate) was used to gel the electrolyte system, the power efficiency of DSSC with Ru-S dye was 6.96% but increased to 7.57% after crosslinking with GPTA. Notably, both DSSCs showed a good long-term stability after one month storage.     

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.     

聚噻吩类化合物在染料敏化太阳能电池中的应用研究进展

阐述了聚噻吩类化合物作为染料敏化剂和电解质在染料敏化太阳能电池中的应用研究进展。     

Synthesis of a novel imidazolium-based electrolytes and application for dye-sensitized solar cells

A series of new imidazolium-based oligomers with different length of a poly(ethylene glycol) moiety as a linker were synthesized and studied as electrolytes for dye-sensitized solar cell (DSSC). These oligomeric molecules are expected to have an intra- or inter-molecular hydrogen bonding interaction through its urethane and urea bonds. They can be used to prepare the liquid-type electrolytes for DSSC by dissolving them into conventional solvent system or to develop solvent-free electrolytes by incorporating an extra redox mediator and other functional materials together as additives. It was found that these oligomers could replace the cationic component of the conventional electrolytes and became the source of redox species when iodine is added. The photocurrent-voltage characteristics of DSSCs with the electrolytes containing these oligomers demonstrated that they can successfully replace the conventional ionic liquid-type electrolytes such as 1-methyl-3-propyl imidazolium iodide (PMII) in 3-methoxypropionitrile (MPN) if the length of the linker is optimized.     

The preparation of poly(glycidyl acrylate)-polypyrrole gel-electrolyte and its application in dye-sensitized solar cells

A microporous hybrid of poly(glycidyl acrylate)-polypyrrole (PGA-PPy) was synthesized by a two-step solution polymerization. Using this hybrid as polymer host, a gel-electrolyte with high conductivity of 12.83 mS cm⁻¹ was prepared. The researches by scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and cyclic voltammetry (CV) show that the microporous structure and functional groups for PGA allows the higher absorbency and good ionic salt tolerance for the electrolyte, the introduction of PPy causes a lower charge-transfer resistance and higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction for the electrolyte. Based on the electrolyte, a dye-sensitized solar cell with a light-to-electrical energy conversion efficiency of 5.03% is achieved, under illumination with a simulated solar light of 100 mW cm⁻² (AM 1.5).     

Preparation of nanostructure mixed copper-zinc oxide via co-precipitation rout for dye-sensitized solar cells: The influence of blocking layer and Co(II)/Co(III) complex redox shuttle

Mixed copper-zinc oxide nanostructures (average size 43 nm) were effectively fabricated via co-precipitation route. Field-emission scanning electron microscope (FESEM), powder X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR) and UV–vis diffuse reflectance spectrum (DRS) were used to characterize the properties of the oxides. At the optimized condition, copper-zinc oxide nanostructures were used for fabrication of working electrodes by doctor blade technique on the fluorine-doped tin oxide (FTO) in dye sensitized solar cells. Their photovoltaic behavior were compared with standard using D35 dye and an electrolyte containing [Co(bpy)₃](PF₆)₂, [Co(pby)₃](PF₆)₃, LiClO₄, and 4-tert-butylpyridine (TBP). The ranges of short-circuit current (J_sc) from 0.13 to 0.30 (mA/cm²), open-circuit voltage (V_oc) from 0.20 to 0.51 V, and fill factor from 0.34 to 0.29 were obtained for the DSSCs made using the working electrodes. A titania blocking layer on the copper-zinc oxide surface improve both the open-circuit voltage (V_oc), short-circuit current (J_sc) and the power-conversion efficiency is consequently enhanced by a factor of approximately five.     

Fabrication of thin film nanocrystalline TiO2 solar cells using ruthenium complexes with carboxyl and sulfonyl groups

Two ruthenium complexes with carboxyl and sulfonyl groups have been synthesized, [Ru^II(L1)₂(NCS)₂] Ru^IIbis(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)-di(thiocyanate) [K313], [Ru^II(L1)₂(dcbpy)] Ru^II bis(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)(4,4′-dicarboxy-2,2′-bipyridyl) [K314] as photosensitizers. UV–vis, fluorescence emission, AFM and CV measurements are also supplied for ruthenium complexes. Photovoltaic properties of dye sensitized nanocrystalline semiconductor solar cells based on Ruthenium complexes which bear carboxyl and sunfonyl groups have been tested under standard AM 1.5 sunlight. Under the standard global AM 1.5 solar conditions, K314 and K313-sensitized solar cells demonstrate short circuit photocurrent densities of 14.92 mA/cm² and 11.23 mA/cm² and overall conversion efficiencies of 5.09% and 4.02%, respectively.     

NMF effect on photosensitized charge separation using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes

The solvent effects on the photosensitized charge separation using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes (RuQPIm), in which bis(2,2′-bipyridine)ruthenium(II) complexes are coordinated to the imidazolyl residues on the poly(1-vinylimidazole) partially quaternized by 1-bromohexadecane and the degree of quaternization is 19 (RuQPIm-19) and 44 (RuQPIm-44) molar percentage, have been investigated in methanol and methanol–NMF (NMF: N-methylformamide). These systems consist of RuQPIm-19 and RuQPIm-44 as photosensitizers, 1,1′-dimethyl-4,4′-bipyridinium dication (MV²⁺) and 1,1′-didodecyl-4,4′-bipyridinium dication (C₁₂V²⁺) as electron acceptors, and triethanolamine (TEOA) as a sacrificial donor. The addition of NMF mainly affect the forward and back reactions in the charge separation reactions. In RuQPIm-19 systems, the reaction proceeds through an interactive process, which is through the viologen having π–π interaction for MV²⁺ and van der Waals interaction for C₁₂V²⁺. In contrast, the reaction proceeds through a direct process by MV²⁺ having no interaction and through an interactive process by C₁₂V²⁺ undergoing van der Waals interaction with the polymer for RuQPIm-44 systems. For MV²⁺, the rates of MV^·+ formation increased, although the quenching efficiency decreased with increasing NMF content for RuQPIm-19 and RuQPIm-44. These results are attributed to stabilization of MV^·+ species by π–π interaction for RuQPIm-19 and steric repulsion between MV^·+ species and RuQPIm-44; namely, the restriction of the back reactions by these effects. In contrast, for C₁₂V²⁺, the rates of C₁₂V^·+ formation decreased and the quenching efficiency increased with the addition of NMF. These are attributed to that the addition of NMF increases the van der Waals interaction of the C₁₂V²⁺ with these polymers and the diffusion of the C₁₂V^·+ species into the bulk solution; namely, the back reaction is accelerated. Furthermore, it is suggested that the conformational changes in these polymers contribute to the charge separation reaction.     

The preparation of titania nanotubes and its application in flexible dye-sensitized solar cells

Anatase titania nanotube (TNT) is prepared by two-steps hydrothermal growth method. Using the TNTs and titania particles (P25), a highly stable and uniform titania colloid without any sedimentation in 180 days is prepared by hydrothermal treatment. Based on the titania colloid, a flexible dye-sensitized solar cell (DSSC) is fabricated at low temperature. The influence of preparation conditions on the properties of TNTs and titania colloid is discussed by transmitting electron microscopy, scanning electron microscopy, selected area electron diffraction, X-ray diffraction, UV-vis absorption spectra, and Brunauer-Emmet-Teller surface area measurements. Under an optimized condition, a flexible DSSC with light-to-electric energy conversion efficiency of 4.0% is achieved under a simulated solar light irradiation of 100 mW cm⁻² (AM 1.5).     

Synthesis and applications of 3,6-carbazole-based conjugated side-chain copolymers containing complexes of 1,10-phenanthroline with Zn(II), Cd(II) and Ni(II) for dye-sensitized solar cells

Three novel donor-acceptor polymeric metal complexes based on polycarbazole containing complexes of 1,10-phenanthroline with Zn(II), Cd(II) and Ni(II) have been synthesized by the Ullmann reaction and characterized by gel permeation chromatography, FT-IR, UV-visible absorption and photoluminescence spectroscopy, cyclic voltammetry and elemental analysis. The application of these organometallic polymers in fabricated dye-sensitized solar cells has been studied. The solar cells exhibited good device performance with a power conversion efficiency of up to 0.44%, under simulated air mass 1.5 G solar irradiation.     

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.     

Polymer–metal complex as gel electrolyte for quasi-solid-state dye-sensitized solar cells

A kind of polymer–metal complex gel electrolyte is successfully prepared and is used in dye-sensitized solar cells. Raman and X-ray photoelectron spectroscopy confirm the structure of this complex and is found that the metal ion reacts with nitrogen in the polymer. This novel electrolyte shows apparent diffusion coefficient of iodide of 8.37 × 10⁻⁷ cm² s⁻¹ and the energy conversion efficiency of 6.10% when the amount of ZnI₂ is 0.04 M. By studying the dissociation active energy of the inorganic salt in electrolytes, we find that the metal salts can dissociate more easily after reacting with polymer and as a result can provide extra free iodide ion. The cell maintains ca. 93% of its initial efficiency after 20 d without further sealing, which shows good long-time stability.     

Ionic liquid/polymer composite electrolytes by in situ photopolymerization and their application in dye-sensitized solar cells

A new kind of quasi-solid state electrolytes for dye-sensitized solar cells (DSCs) has been prepared by in situ photopolymerization from the precursor 1,6-hexanediol diacrylate (HDDA) in 1-hexyl-3-methyl imidazolium iodide (HMII). The optimal ratio of polymer/ionic liquid is determined by the conductivities of the electrolytes. In order to further increase the miscibility between ionic liquid and the polymer, oligomer polyethylene glycol dimethyl ether (PEGDME) is introduced. By optimization of the amount of PEGDME in the electrolyte, the DSCs using this kind of solid-state electrolytes can present 6.5% of light-to-electricity conversion efficiency under 41 mW cm⁻². In the meantime, the influence of PEGDME additive is detailedly investigated by electrochemical impedance spectrum (EIS) and intensity modulated photovoltage spectroscopy (IMVS) techniques. Preliminary long-term stability test revealed that this in situ photopolymerized electrolyte exhibits good stability after 1000 h thermal test.     

TiO2 micro-flowers composed of nanotubes and their application to dye-sensitized solar cells

TiO₂ micro-flowers were made to bloom on Ti foil by the anodic oxidation of Ti-protruding dots with a cylindrical shape. Arrays of the Ti-protruding dots were prepared by photolithography, which consisted of coating the photoresists, attaching a patterned mask, illuminating with UV light, etching the Ti surface by reactive ion etching (RIE), and stripping the photoresist on the Ti foil. The procedure for the blooming of the TiO₂ micro-flowers was analyzed by field emission scanning electron microscopy (FESEM) as the anodizing time was increased. Photoelectrodes of dye-sensitized solar cells (DSCs) were fabricated using TiO₂ micro-flowers. Bare TiO₂ nanotube arrays were used for reference samples. The short-circuit current (J_sc) and the power conversion efficiency of the DSCs based on the TiO₂ micro-flowers were 4.340 mA/cm² and 1.517%, respectively. These values of DSCs based on TiO₂ micro-flowers were higher than those of bare samples. The TiO₂ micro-flowers had a larger surface area for dye adsorption compared to bare TiO₂ nanotube arrays, resulting in improved J_sc characteristics. The structure of the TiO₂ micro-flowers allowed it to adsorb dyes very effectively, also demonstrating the potential to achieve higher power conversion efficiency levels for DSCs compared to a bare TiO₂ nanotube array structure and the conventional TiO₂ nanoparticle structure.     

New diketo-pyrrolo-pyrrole (DPP) sensitizer containing a furan moiety for efficient and stable dye-sensitized solar cells

A new metal-free organic sensitizer containing a furan moiety as the π-spacer based on the diketo-pyrrolo-pyrrole unit was synthesized through simple synthetic routes and with low cost for the application of dye-sensitized solar cells. Two corresponding dyes with benzene and thiophene spacers were also synthesized for the purpose of comparison. On the basis of optimized DSSC test conditions, the sensitizer containing the furan shows prominent solar energy conversion efficiency (η) of 5.65% (J_sc = 15.96 mA cm⁻², V_oc = 541 mV, ff = 0.65) under simulated full sunlight irradiation. The dyes were also tested in a solvent-free ionic liquid electrolyte devices and the stability of devices was performed over 2000 h at full sunlight. The sensitizer containing the furan moiety exhibited good stability and better photovoltaic performance of up to 4.41% power conversion efficiency.     

Electro-optical properties of new anthracene based organic dyes for dye-sensitized solar cells

Dipolar compounds containing anthracene-based triarylamine donor and cyanoacrylic acid acceptor were synthesized and characterized by electro-optical measurements. The optical spectra of the dyes are dominated by a charge transfer transition. This band is red-shifted and increased in intensity on elongation of conjugation by the introduction of bithiophene or dithienylbenzothiadiazole moiety. Similarly, the oxidation potentials of the dyes are shifted anodically on extension of the conjugation attributable to the reduction in the interaction between the triarylamine and acceptor segments. Theoretical calculations revealed the charge transfer to occur between anthracene and triarylamine moieties. However, in the benzothiadiazole containing dye the charge transfer is observed between the amine and the acceptor segment. Dye-sensitized solar cells fabricated using these dyes showed moderate efficiency which is highly dependent on the nature of the conjugation bridge.     

Preparation and characterization of core-shell electrodes for application in gel electrolyte-based dye-sensitized solar cells

Core-shell electrodes based on TiO₂ covered with different oxides were prepared and characterized. These electrodes were applied in gel electrolyte-based dye-sensitized solar cells (DSSC). The TiO₂ electrodes were prepared from TiO₂ powder (P25 Degussa) and coated with thin layers of Al₂O₃, MgO, Nb₂O₅, and SrTiO₃ prepared by the sol-gel method. The core-shell electrodes were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy measurements. J-V curves in the dark and under standard AM 1.5 conditions and photovoltage decay measurements under open-circuit conditions were carried out in order to evaluate the influence of the oxide layer on the charge recombination dynamics and on the device's performance. The results indicated an improvement in the conversion efficiency as a result of an increase in the open circuit voltage. The photovoltage decay curves under open-circuit conditions showed that the core-shell electrodes provide longer electron lifetime values compared to uncoated TiO₂ electrodes, corroborating with a minimization in the recombination losses at the nanoparticle surface/electrolyte interface. This is the first time that a study has been applied to DSSC based on gel polymer electrolyte. The optimum performance was achieved by solar cells based on TiO₂/MgO core-shell electrodes: fill factor of ∼0.60, short-circuit current density J_sc of 12 mA cm⁻², open-circuit voltage V_oc of 0.78 V and overall energy conversion efficiency of ∼5% (under illumination of 100 mW cm⁻²).     

High-performance and low platinum loading electrodeposited-Pt counter electrodes for dye-sensitized solar cells

This study demonstrates platinum (Pt) counter electrodes with low charge-transfer resistance (R_ct), low Pt loading and high active surface area can be obtained within 30 s by using the direct-current deposition in the presence of 3-(2-aminoethylamino)propyl-methyldimethoxysilane (Me-EDA-Si) as an additive. The addition of appropriate Me-EDA-Si can not only enhance the current efficiency but also inhibit the growth of semicircle-like grains, thus resulting in Pt electrode with high active surface area. Consequently, the dye-sensitized solar cells (DSSCs) fabricated with so-prepared Pt electrodes exhibited cell efficiency of 7.39% while 0.01 vol% Me-EDA-Si was added, which is much superior to that with sputtered-Pt electrodes under the same assembly conditions.     

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).     

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.