Effects of anchoring groups in multi-anchoring organic dyes with thiophene bridge for dye-sensitized solar cells

Organic photo-sensitizers were designed and synthesized based on a phenothiazine framework containing single- and double-electron acceptors that were bridged with thiophene for the dye sensitized solar cells (DSSCs). The optimized geometries were determined with density functional theory (DFT) calculations to estimate the photovoltaic properties of the dyes in the design stage. The organic dye with the double electron acceptors exhibited a better light absorption at long wavelength and an effective electron extraction pathway from the electron donor to the TiO₂ surface, leading to an improved short-circuit current (11.6 mA cm^?2), compared with that of the dye with the single electron acceptor (10.2 mA cm^?2) and the conventional N3 Ru-dye (10.4 mA cm^?2). Contrarily, the open-circuit voltage of the organic dye with the double electron acceptors decreased because the additional protonated carboxylic groups caused a positive shift in the Fermi level of TiO₂.     

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.     

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%.     

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 characterization of a novel fullerene derivative containing carbazole group for use in organic solar cells

A novel carbazole-group-containing fullerene derivative (CBZ-C₆₀) with good solubility in common organic solvents was synthesized. This derivative was analyzed by using many techniques such as NMR, FAB-MS, FTIR and UV–vis absorption spectroscopy. Further, bulk heterojunction photovoltaic devices were fabricated. Since the LUMO energy level of CBZ-C₆₀ was higher than that of fullerene, the open-circuit voltage (V_oc) of devices based on CBZ-C₆₀ was higher than that of devices based on fullerene. The power-conversion efficiency was highest for devices with composite thin films that have P3HT/CBZ-C₆₀ composition ratios of 1:1 and were annealed at 150 °C for 10 min. The maximum V_oc, short-circuit current density, and PCE of the best device were 0.64 V, 2.32 mA/cm², and 0.48%, respectively.     

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.     

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%。     

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 ...     

Synthesis and characterization of polyimides from triphenylamine-based diamine monomers with thiophene or trifluoromethyl side group

Triphenylamine-based novel diamine monomers with side group, such as 4-(2,2′-bithiophenyl)-4′,4″-diaminotriphenylamine (2TTPA) and 4-(3,5-bis(trifluoromehyl)phenyl)-4′,4″-diaminotriphenylamine (6FTPA) were prepared and used for polyimide synthesis. 4-Bromo-dinitrotriphenylamine (BrTPA), prepared from 4-bromoaniline and 1-fluoro-4-nitrobenzene, was reacted with 2,2′-bithiophenene-5-boronic acid (2TBB) or 3,5-bis(trifluoromethyl)benzeneboronic acid (6FBB), followed by hydrogenation to afford 2TTPA and 6FTPA, respectively. After characterization by FT-IR, ¹H-NMR, EA and melting point analyzer, the triphenylamine-based dimaines were utilized to prepare polyimides with 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) or 2,2-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The polymers were characterized by FT-IR and ¹H-NMR. Thermal, optical and electrical properties were also evaluated by DSC/TGA, UV–vis/photoluminescence spectrometery and cyclic voltammetry (CV), respectively. The 6FDA–6FTPA polyimide exhibited high glass transition temperatures (291 °C), high thermal stability (>488 °C) and light blue emission (480 nm) with very good solubility even after imidization.     

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.     

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.     

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.     

Synthesis and characterization of organic photorefractive glass

Bifunctional molecule, which possesses photoconductive and electrooptic properties in one molecule, was synthesized as a new photorefractive material. Carbazole as a photoconductive moiety was covalently bound to thiophene derivative as an electrooptic chromophore via a flexible alkyl chain. The sample prepared from the mixture of bifunctional molecule (89 wt.%), 2,4,7-trinitro-9-fluorenone (1 wt.%) and ethylcarbazole (10 wt.%) showed good photorefractive property. The 50 μm thick film showed the maximum diffraction efficiency of 65% at 70 V/μm, corresponding to a refractive index modulation (Δn) of ca. 4.5×10⁻³.     

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.     

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.     

CNT/PEDOT core/shell nanostructures as a counter electrode for dye-sensitized solar cells

CNT/PEDOT nanostructures composed of carbon nanotube (CNT) cores and poly(3,4-ethylenedioxythiophene) (PEDOT) shells were synthesized by chemical oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT) using FeCl₃ and dodecylbenzene sulfonic acid (DBSA) as the oxidant and surfactant, respectively. The resulting CNT/PEDOT nanostructures had a PEDOT layer thickness of 2–5 nm that exhibited not only higher polymerization yield but also enhanced thermal stability and electrical conductivity relative to pure PEDOT. N-Methyl-2-pyrrolidone (NMP)-based CNT/PEDOT paste containing polyvinylidene fluoride (PVDF) as a binder was painted directly onto fluorine-doped tin oxide (FTO) glass for use as a counter electrode (CE) material in dye-sensitized solar cells (DSSCs). While DSSCs made of pure CNT and PEDOT CE exhibited power conversion efficiencies of ～3.88% and 4.32% under standard AM 1.5 sunlight illumination, respectively, the cell efficiency was enhanced to ～4.62% with the CNT/PEDOT CE. This enhancement was due to the improved fill factor of the CNT/PEDOT-based DSSC realized by the increased electrical conductivity of the CNT/PEDOT composite.     

Facile synthesis of ZnO nanobullets/nanoflakes and their applications to dye-sensitized solar cells

In this paper we reported a successful synthesis of ZnO nanobullets/nanoflakes by a simple hydro/solvothermal method employing a mixture of water/ethylene glycol as the solvent, and zinc acetate as the zinc source. The final products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Raman scattering and photofluorescence spectra of the products were also investigated. ZnO with both nanobullets and nanoflakes nanostructures had been comparably studied as active photoanodes in dye-sensitized solar cell (DSSC) system, and the overall light-to-energy conversion efficiency of 1.93% has been achieved for nanobullets based DSSC, while that for ZnO nanoflakes based DSSC has been raised up to 3.64%.     

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.     

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.