Two-dimensional X-shaped organic dyes bearing two anchoring groups to TiO2 photoanode for efficient dye-sensitized solar cells

Novel two-dimensional X-shaped donor–π–acceptor (D–π–A)-type dyes were designed and successfully synthesized for use in a dye-sensitized solar cell (DSSC). Two triphenylamine units in these dyes act as electron donor units, while two cyanoacrylic acid groups act as electron acceptor units and anchoring groups to the TiO₂ photoanode. The photovoltaic properties of the newly synthesized dye-containing DSSCs were investigated to identify the effects of conjugation length between the electron donors and acceptors, and the molecular energy levels of the dyes. Among the three dyes we synthesized, (2E,2′E)-3,3′-(5′,5″-(4,5-bis(4-(bis(4-tert-butylphenyl)amino)styryl)-1,2-phenylene)bis(2,2′-bithiophene-5′,5-diyl))bis(2-cyanoacrylic acid) (11) showed the highest power conversion efficiency of 3.14% (η_max = 4.06% with TiCl₄ treatment) under AM 1.5G illumination (100 mW cm⁻²) in a photoactive area of 0.418 cm² with short circuit current density of 7.27 mA cm⁻², open circuit photovoltage of 612 mV, and a fill factor of 70.6%.     

Synthesis and characterization of triphenylamine-based organic dyes for dye-sensitized solar cells

We synthesized three organic dyes (DYE 1, DYE 2, and DYE 3) containing triphenylamine (TPA) moieties as electron donors and cyanoacrylic acid moieties as electron acceptors, designed at the molecular level, and developed them for use in dye-sensitized solar cells (DSSCs). Among all the dyes, DYE 2 exhibited the highest overall solar-energy-to-electricity conversion efficiency of 4.06% with a short-circuit photocurrent density of 11.15 mA cm^?2, an open-circuit voltage of 0.64 V, and a fill factor of 0.57 under AM 1.5 irradiation with 100 mW cm^?2 simulated sunlight. The results indicate that the organic dyes are promising in the development of DSSC.     

D-π-A organic dyes with carbazole as donor for dye-sensitized solar cells

Two donor-π-acceptor (D-π-A) organic dyes with carbazole as donor, phenylethynyl, thienylethynyl as π-spacers and cyanoacrylic acid as acceptor, have been synthesized and characterized. These dyes exhibit charge transfer character in the ground and excited states as supported by the UV–vis and fluorescence studies. They also show interesting electrochemical properties. DFT and TDDFT studies reveal that large intramolecular charge transfer takes place from the HOMO to LUMO, though the donor carbazole is twisted (～51°) with respect to the π-conjugated spacer and acceptors with an idea of testing the dyes as sensitizers for DSSC. The DSSC devices were fabricated with these dyes by using redox electrolyte in a nonvolatile methoxypropionitrile solvent. The efficiency of the cells, short circuit current density, J_sc, and open circuit photovoltage, V_oc, and fill factor, FF, has been obtained for the two molecules. Calculations based on DFT plane wave method reveal the strong binding of the dyes on the surface of TiO₂ (1 0 1) surface. It is concluded that these dyes can play the role of sensitizers in DSSC.     

Organic photosensitizers with N-carboxymethyl pyridinium acceptor/anchoring group for dye-sensitized solar cells

Four new organic dyes with N-carboxymethyl pyridinium as electron acceptors/anchoring groups were designed and synthesized. The optical and electrochemical properties were characterized by UV–vis, fluorescence spectroscopy and cyclic voltammetry. The absorption spectra of the four pyridinium dyes were in the range of 450–650 nm. The dye with triphenylamine as the electron donor shows a solar-energy-to-electricity conversion efficiency (η) of 2.33% in comparison with the reference Ru-complex (N719 dye) with a η value of 5.45% under the same experimental conditions. The dye with phenoxazine as the electron donor gives broad IPCE spectra in the range of 400–750 nm. All these new dyes are simple in structure, very easy to synthesize, and gives high V_oc.     

A phenylenevinylene copolymer with perylene bisimde units as organic sensitizer for dye-sensitized solar cells

An alternating phenylenevinylene copolymer P with perylene bisimide units has been used as organic sensitizer to fabricate dye-sensitized solar cells (DSSCs) based on porous and TiCl₄ modified TiO₂ photoelectrodes. As a consequence of the compact layer formed by TiCl₄ treatment to the porous TiO₂ thin film layer, an efficient electron network was formed. Dark current measurements and electrochemical impedance spectra (EIS) suggested that modified photoelectrode significantly reduced the recombination rate of electrons with redox couple in the electrolyte due to the reduced bare FTO surface and longer electron lifetime as compared to the porous TiO₂ photoelectrode. The power conversion efficiency of DSSCs utilizing this copolymer as sensitizer is about 2.60% and 3.98% with porous and modified TiO₂ photoelectrodes, respectively.     

Synthesis and photovoltaic performance of new diketopyrrolopyrrole (DPP) dyes for dye-sensitized solar cells

Two new metal-free organic dyes (DPP-I and DPP-II) with diketopyrrolopyrrole (DPP) core were designed and synthesized, in which triphenylamine or N,N-bis(4-methoxyphenyl)benzenamine moieties was used as the electron donor, DPP units as the π-conjugated bridge, and carboxylic acid group as the electron acceptor. Photophysical and electrochemical properties of two dyes were investigated by UV–vis spectrometry and cyclic voltammetry. Electrochemical measurement data indicate that the tuning of the HOMO and LUMO energy levels can be conveniently accomplished by alternating the donor moiety. The DSSC based on dye DPP-I showed better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 80.6% corresponding to an overall conversion efficiency of 2.68%. Although the power conversion efficiencies are not so high, this work explores new donor–π-accepter–π-donor models and the effects of molecular design on optical properties.     

New fluoranthene-based cyanine dye for dye-sensitized solar cells

In this paper, a new fluoranthene-based unsymmetrical organic cyanine dye I and the corresponding cyanine dye II containing ethynyl unit for the purpose of comparison were designed and synthesized as sensitizers for the application in dye-sensitized solar cells (DSSCs). The absorption spectra, electrochemical and photovoltaic properties of I and II were extensively investigated. The DSSCs based on the fluoranthene dye I showed the better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 67%, a short-circuit photocurrent density (J_sc) of 7.83 mA cm^?2, an open-circuit photovoltage (V_oc) of 0.476 V, and a fill factor (ff) of 0.63, corresponding to an overall conversion efficiency of 2.34% under simulated AM 1.5G solar light condition. Also, the effects of chenodeoxycholic acid (CDCA) in a solution as a co-adsorbate on the photovoltaic performance of DSSCs based on cyanine dyes were also investigated. The presence of CDCA for 0.5 h, increases both the photovoltage and photocurrent of the DSSC incorporating I, in which the photovoltage and photocurrent increase 9.3% and 20%, respectively. The above photovoltaic results indicate that coadsorption of appropriate amount CDCA is effective to improve solar cell performance.     

Effects of surface-modified photoelectrode on the power conversion efficiency of dye-sensitized solar cells

The effects of Na₂SO₄ as a surface modification material on the performance of dye-sensitized solar cells (DSSCs) were studied. The surfaces of TiO₂ films were firstly modified with aqueous Na₂SO₄ solution by a dip coating process, and then the resulting electrode was applied to the photoelectrode of a DSSC. The DSSC with the Na₂SO₄-modified photoelectrode had a power conversion efficiency of 9.01% compared with that (7.97%) of the reference cell, which corresponds to an increase of about 13.0% in the efficiency due to an enhancement in short-circuit current (J _sc ) and open-circuit voltage (V _oc ). A series of measurements such as UV-visible absorption, electrochemical impedance, incident photon to current conversion (IPCE) efficiency and dark current revealed that incorporation of Na₂SO₄ onto the TiO₂ film led to an increase of dye adsorption and a longer lifetime of electrons injected from dyes to the TiO₂ electrodes, resulting in the improvement in both J _sc and V _oc , compared to those of a reference device without surface modification.     

碳纳米复合对电极染料敏化太阳能电池的电化学性能

在染料敏化太阳能电池(DSCs)碳对电极中添加多壁碳纳米管,制作碳纳米复合对电极。通过循环伏安法研究复合电极中碳纳米管对I3?/I?氧化还原行为的影响。采用电化学阻抗谱表征,比较纳米炭黑、石墨鳞片、碳纳米管、纳米炭黑-纳米碳管复合材料对碳电极/电解质界面的影响。结果表明:添加纳米碳管后,电极的催化还原电位降低,电流密度增大;碳纳米管的加入使电极表面催化活性点增多,碳电极与电解液的界面电势差减少。光伏性能测试表明,添加10%(质量分数)的碳纳米管的DSCs的开路电压提高了17.9%,短路电流提高了24.1%,填充因子提高了14.4%。     

Investigation of new PPV-type polymeric materials containing fluorene and thiophene units and their application in organic solar cells

New poly(p-phenylenevinylene) (PPV)-type conducting polymers containing different concentrations of thiophene and fluorene functional units were investigated in this work and the photophysical and electrochemical properties were evaluated. We observed a dependence of these properties on the concentration of thiophene units in the polymer backbone. The hole mobilities were estimated to be on the order of 10^?6 cm² V^?1 s^?1. The polymers were combined with different concentrations of a soluble fullerene derivative (PCBM) and applied in bulk-heterojunction photovoltaic cells. The effects of PCBM concentration and of annealing (post-production treatment) on these devices were investigated. The best results were obtained for the materials containing higher concentrations of thiophene units.     

Solvothermal growth of Zn2SnO4 for efficient dye-sensitized solar cells

Zn2SnO4 plates,particles and spheres are suc-cessfully prepared via a facile synthesis way by carefully adjusting the solvothermal conditions,which are further ...     

Novel bilayer structure ZnO based photoanode for enhancing conversion efficiency in dye-sensitized solar cells

ZnO film with a novel bilayer structure, which consists of ZnO nanowire (ZnO NW) arrays as underlayer and polydisperse ZnO nanocrystallite aggregates (ZnO NCAs) as overlayer, is fabricated and studied as dye-sensitized solar-cell (DSSC) photoanode. Results indicate that such a configuration of the ZnO nanocrystallite aggregates on the ZnO nanowire arrays (ZnO-(NCAs/NWs)) can significantly improve the efficiency of the DSSC due to its fast electron transport, relatively high surface area and enhanced light-scattering capability. The short-circuit current density (J_sc) and the energy-conversion efficiency (η) of the DSSC based on the ZnO-(NCAs/NWs) photoanode are estimated and the values are 9.19 mA cm⁻² and 3.02%, respectively, which are much better than those of the cells formed only by the ZnO NWs (J_sc = 4.02 mA cm⁻², η = 1.04%) or the ZnO NCAs (J_sc = 7.14 mA cm⁻², η = 2.56%) photoanode. Moreover, the electron transport properties of the DSSC based on the ZnO-(NCAs/NWs) photoanode are also discussed.     

Benzothiadiazole-sandwiched quarter thiophene-based oligomer for organic solar cells

A novel diphenylaminofluorenyl-capped benzothiadiazole-sandwiched quarter thiophene-based narrow band-gap oligomer 4,7-bis-{[5-(9,9-bis(octyl)-7-diphenylaminofluorene-2-yl)-thiophen-2-yl]-5-thiophen-2-yl}-[2,1,3] benzothiadiazole (DPAFL–DBBT–DPAFL which is further abbreviated to DDBBTD) has been synthesized and characterized. The obtained molecule absorbs light from 300 to 800 nm in solid film. PL peak of DDBBTD in solid film is centered at 731 nm. Photovoltaic cell by using the blend of the obtained oligomer and PCBM as active layer was fabricated by spin-coating method. Open-circuit voltage reached 0.85 V with the maximum energy conversion efficiency 0.15% and photocurrent response was extended over 700 nm.     

Co-sensitization with near-IR absorbing cyanine dye to improve photoelectric conversion of dye-sensitized solar cells

Two carboxylated cyanine dyes, 3-butyl-2-[3-(1-butyl-5-carboxy-1,3-dihydro-3,3-dimethyl-2H-indol-2-ylidene)-1-propen-1-yl]-1,1-dimethyl-7-[1-[2-[6-(4-morpholinyl)-1,3-dioxo-1H-benz[de]isoquinolin-2(3H)-yl]ethyl]-1H-1,2,3-triazol-4-yl]-1H-Benz[e]indolium iodide (A), 2-[5-(1-butyl-5-carboxy-1,3-dihydro-3,3-dimethyl-2H-indol-2-ylidene)-1,3-pentadienyl]-3-ethyl-1,1-dimethyl-1H-Benz[e]indolium iodide (B), have been prepared and their photophysical and electrochemical properties have been investigated. A, B and their mixtures (AB) were used as sensitizers in nanocrystalline TiO₂ solar cells to improve photoelectric conversion efficiency. It was found that the solar cell sensitized with A3B1 (molar ratio: A:B = 3:1) generated a high power conversion efficiency of 3.0% under AM1.5G illumination (100 mW cm⁻²), indicating that co-sensitization is a promising method to improve the photoelectrical properties of dye-sensitized solar cells.     

Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells

We describe a method to fill thin films of nanoporous TiO₂ with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO₂/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.     

Solar energy-conversion processes in organic solar cells

Organic semiconducting materials have demonstrated attractive light-absorption and photocurrent-generation functions due to their delocalized π electrons as well as intra-molecular and inter-molecular charge separation processes. On the other hand, organic semiconducting materials have easy property tuning, are mechanically flexible, and have large-area thin film formation properties. As a result, organic materials have become potential candidates in solar energy applications. This article will review critical energy-conversion processes in organic solar cells with the focus on singlet and triplet photovoltaic responses.     

Micro-mountain and nano-forest pancake structure of Nb2O5 with surface nanowires for dye-sensitized solar cells

Niobium oxide produced by an anodization process for application in a high-efficiency dye-sensitized solar cell (DSSC) has been reported. In order to increase the energy conversion efficiency of the cell, we demonstrated niobium oxide micro-mountain and nano-forest pancake structures that contained nanowires on the surface. The increase in efficiency is attributed to the significantly enhanced surface area, which allows for more dye loading and light harvesting, as well as the reduced charge recombination, which provides direct conduction pathways along the crystalline Nb₂O₅ micro-mountain structures with nanowires. We observed that the photovoltaic performance of the Nb₂O₅ DSSC increased from 1.03% to 3.35% when the oxide thickness was increased from 9.3 μm to 27.7 μm. Since the anodization process is very cheap and takes place at low temperatures, it has substantial potential for the further development of DSSCs with metal-oxide nano-materials. Anodized oxide advantage is that essentially any form of a niobium surface can be treated in a quick and low-cost approach with Nb₂O₅ coating.     

Gel electrolytes containing several kinds of particles used in quasi-solid-state dye-sensitized solar cells

Composite gel electrolytes containing several kinds of particles used as the quasi-solid-state electrolytes in dye-sensitized solar cells (DSSCs) were reported. Mesoporous particles (MCM-41) with unique structures composed of ordered nanochannels were served as a new kind of gelator for quasi-solid-state electrolytes. MCM-41, hydrophobic fumed silica Aerosil R972 and TiO2 nanopatricles P25 were dispersed into gel electrolytes respectively. The solar energy-to-electricity conversion efficiency of these cells is 4.65%, 6.85% and 5.05% respectively under 30 mW·cm-2 illumination. The preparation methods and the particles sizes exert an influence on the performance of corresponding solar cells. Owing to unique pore structures and high specific BET surface area, mesoporous silica MCM-41 was expected to have the potential to afford conducting nanochannels for redox couple diffusion.     

Molecular design of donor–acceptor-type cruciform dyes for efficient dyes-sensitized solar cells

Novel donor–acceptor (D–A) type cruciform dyes were synthesized for use in a dye-sensitized solar cell. The geometries and electronic structures of the dyes were designed by the results of density functional theory (DFT) calculations. Two phenothiazine units in these dyes act as electron donors, while two cyanoacrylic acid groups act as electron acceptors. The solubility of these compounds is increased because of the presence of the hexyl groups in the phenothiazine rings. The photovoltaic properties of 14D-25A and 12A-45D were measured to identify the effects of the dye having two electron donors and two electron acceptors on the DSSC performance. The 12A-45D dye showed a power conversion efficiency of 4.5% under AM 1.5 illumination (100 mW cm^?2) in an photoactive area of 0.42 cm², short circuit current density of 10.8 mA cm^?2, open circuit photovoltage of 0.65 V and a fill factor of 64%.