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Three new metal-free organic dyes with the [1]benzothieno[3,2-b]benzothiophene (BTBT) p-bridge, having the structure donor-p-acceptor (D-π-A) and labeled as 19, 20 and 21, have been designed and synthesized for application in dye-sensitized solar cells (DSSC). Once the design of the π-acceptor block was fixed, containing the BTBT as the π-bridge and the cyanoacrylic group as the electron acceptor and anchoring unit, we selected three donor units with different electron-donor capacity, in order to assemble new chromophores with high molar extinction coefficients (ε), whose absorption features well reflect the good performance of the final DSSC devices. Starting with the 19 dye, which shows a molar extinction coefficient ε of over 14,000 M-1 cm-1 and takes into account the absorption maximun at the longer wavelength, the substitution of the BFT donor unit with the BFA yields a great enhancement of absorptivity (molar extinction coefficient ε > 42,000 M-1 cm-1), until reaching the higher value (ε > 69,000 M-1 cm-1) with the BFPhz donor unit. The good general photovoltaic performances obtained with the three dyes highlight the suitable properties of electron-transport of the BTBT as the π-bridge in organic chromophore for DSSC, making this very cheap and easy to synthesize molecule particularly attractive for efficient and low-cost photovoltaic devices. [ABSTRACT FROM AUTHOR]

A new synthetic strategy for indolo[2,3-b]carbazolevia a double-intramolecular Buchwald–Hartwig reaction has beenestablished. The N-alkylated indolo[2,3-b]carbazole then was adopted as the geometry-fixed core for the synthesisof a new molecule (ICZDTA) bearing two bithiophene π-bridged2-cyanoacrylic acid groups as the bidentate anchor. The bidentateanchoring together with efficient HOMO (indolo[2,3-b]carbazole) → LUMO (TiO2nanocluster) electrontransfer leads to the successful development of ICZDTA-based DSSC with a power conversion efficiency of 6.02%. [ABSTRACT FROM AUTHOR]

The effect of thedonor in an organic dye on the electron lifetimeof dye-sensitized solar cells (DSSCs) employing a cobalt redox electrolytewas investigated. We synthesized organic dyes with donor moietiesof carbazole, coumarin, triphenylamine, and N-phenyl-carbazoleand measured the current–voltage characteristics and electronlifetimes of the DSSCs with these dyes. The cell with the triphenylaminedonor dye produced the highest open circuit voltage and longest electronlifetime. On the other hand, the lowest open circuit voltage and shortestelectron lifetime was obtained with coumarin donor dye, suggestingthat the coumarin attracted the cobalt redox couples to the surfaceof the TiO2layer, thus increasing the concentration ofcobalt complex. On the other hand, the longest electron lifetime withtriphenylamine was attributed to the blocking effect by steric hindranceof the nonplanar structure of the donor. [ABSTRACT FROM AUTHOR]

A major limitation of solid-statedye-sensitized solar cells isa short electron diffusion length, which is due to fast recombinationbetween electrons in the TiO2electron-transporting layerand holes in the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene(Spiro-OMeTAD) hole-transporting layer. In this report, the sensitizingdye that separates the TiO2from the Spiro-OMeTAD was engineeredto slow recombination and increase device performance. Through thesynthesis and characterization of three new organic D-π-A sensitizingdyes (WN1, WN3, and WN3.1), the quantity and placement of alkyl chainson the sensitizing dye were found to play a significant role in thesuppression of recombination. In solid-state devices using Spiro-OMeTADas the hole-transport material, these dyes achieved the followingefficiencies: 4.9% for WN1, 5.9% for WN3, and 6.3% for WN3.1, comparedto 6.6% achieved with Y123 as a reference dye. Of the dyes investigatedin this study, WN3.1 is shown to be the most effective at suppressingrecombination in solid-state dye-sensitized solar cells, using transientphotovoltage and photocurrent measurements. [ABSTRACT FROM AUTHOR]

Two donor--acceptor organic dyes have been synthesized that differ only by a two-heteroatom change from oxygen to sulfur within the donor unit. The two dyes, (E)-3-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid (Dye-O) and (E)-3-(5-(4-(bis(4-(hexykhio)phenyl) amino)phenyl)thiophen-2-yl)-2-cyanoprop-2-enoic acid) (Dye-S), were tested in solar cell devices employing both I3-/I--based and [Co(bpy)3]3+/2+ redox mediators. Power conversion efficiencies over 6% under simulated AM 1.5 illumination (1 Sun) were achieved in both electrolytes. Despite similar optical and redox properties for the two dyes, a consistently higher open-circuit voltage (Voc) was measured for Dye-S relative to Dye-O. The improved efficiency observed with Dye-S in an iodide redox mediator is against the commonly held view that sulfur atoms promote charge recombination attributed to inner-sphere interactions. Detailed mechanistic studies revealed that this is a consequence of a 25-fold enhancement of the regeneration rate constant that enhances the regeneration yield under open circuit conditions. The data show that a high short circuit photocurrent does not imply optimal regeneration efficiency as is often assumed. [ABSTRACT FROM AUTHOR]

An amine-free oligothiophene-based dye (BTB) featuring a tailor-made dianchoring function, a spiro-configured central unit, and bulky end-capping TIPS groups to diminish intermolecular interactions and to suppress aggregation-induced self-quenching was synthesized to achieve efficient dye-sensitized solar cells with a high power conversion efficiency of 6.52%. [ABSTRACT FROM AUTHOR]

Two new organic dyes incorporating triphenylamine as a donor and oligothienylenevinylene as a bridge have been synthesized. The new dyes cover the entire visible region and have a power conversion of up to 6.25%. [ABSTRACT FROM AUTHOR]

An organic dye containing two D-π-A branches linkedwitha thiophene unit has been designed and synthesized for efficient dye-sensitizedsolar cells (DSSCs). As compared to the rod-shape of the single D-π-Aanalogue dye, the cross shape of the double D-π-A branched dyeis favorable for reducing intermolecular interaction and retardingcharge recombination. Controlled intensity modulated photovoltagespectroscopy reveals that electron lifetime for the double D-π-Adye-based DSSC is 14-fold longer than that for the corresponding singleD-π-A dye-based DSSC. Linking two D-π-A branches witha thiophene unit increases open-circuit photovoltage by 100 mV andshort-circuit photocurrent by 4.10 mA cm–2. As aconsequence, power conversion efficiency is enhanced by about 2-fold.This work presents a new route to designing sensitizers with highsuppression ability of charge recombination toward high-performanceDSSCs. [ABSTRACT FROM AUTHOR]

A series of metal-free organic dyes exploiting different combinations of (hetero)cyclic linkers (benzene, thiophene, and thiazole) and bridges (4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) and benzodithiophene (BDT)) as the central π-spacers were synthesized and characterized. Among them, the sensitizer containing the thiophene and CPDT showed the most broad incident photon-to-current conversion efficiency spectra, resulting in a solar energy conversion efficiency (η) of 6.6%. [ABSTRACT FROM AUTHOR]

The determination of the orientation and molecular density for several porphyrin dyes adsorbed on planar TiO2surfaces using X-ray reflectometry (XRR) is reported. Adsorption of nanoscale water layers occurred rapidly upon exposure of freshly prepared TiO2surfaces to ambient conditions; however, this was successfully eliminated, resulting in clearly discernible adsorbed dye layers for sensitized surfaces. Adsorbed dye orientations, determined from computations constrained by the measured dye layer thickness, were calculated to have a binding tilt angle of 35°–40°. Combining the XXR data with the orientation models indicates that the porphyrins form densely packed surfaces with an intermolecular spacing of 3–4 Å, consistent with π–π stacking interactions. Changes in the molecular size of probe dyes were reflected in corresponding changes in the measured dye layer thickness, confirming the ability of this technique to resolve small variations in dye layer thickness and consequently adsorption orientation. Application of these results to understanding the behavior of dye-sensitized devices is discussed. [ABSTRACT FROM AUTHOR]

A new class of organic sensitizers incorporating a benzo[1,2-b:4,5-b′]dithiophene (BDT) unit as conjugated spacer has been synthesized and successfully used for dye-sensitized solar cells (DSSCs). The length of the π-conjugated spacers has a strong impact on electro-optical properties of these dyes, leading to the conversion efficiencies ranging from 4.17 to 5.68% under AM 1.5 G irradiation. This result indicates that the BDT unit is a promising candidate in organic sensitizers. [ABSTRACT FROM AUTHOR]

Nanoporous-walled tungsten oxide (WO3) nanotubes (NTs), which had a more positive conduction band edge level compared to that of TiO2, were applied to various organic dyes for dye-sensitized solar cells (DSSCs). The dye-sensitized WO3NTs displayed photosensitization for the organic dyes whose lowest unoccupied molecular orbital (LUMO) level was relatively positive to the conventional TiO2electrode and, thus, not applicable for electron injection to the TiO2electrode. Electron transport time and electron lifetime for the WO3electrode in the DSSCs were investigated. In comparison to the DSSCs based on TiO2, SnO2, and In2O3, the WO3DSSCs displayed the longest lifetime. On the other hand, non-diffusion-like electron transport may be an issue to apply WO3for the DSSCs. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells (DSCs) with cobalt-based mediators with efficiencies surpassing the record for DSCs with iodide-free electrolytes were developed by selecting a suitable combination of a cobalt polypyridine complex and an organic sensitizer. The effect of the steric properties of two triphenylamine- based organic sensitizers and a series of cobalt polypyridine redox mediators on the overall device performance in DSCs as well as on transport and recombination processes in these devices was compared. The recombination and mass-transport limitations that, previously, have been found to limit the performance of these mediators were avoided by matching the properties of the dye and the cobalt redox mediator. Organic dyes with higher extinction coefficients than the standard ruthenium sensitizers were employed in DSCs in combination with outer-sphere redox mediators, enabling thinner TiO2 films to be used. Recombination was reduced further by introducing insulating butoxyl chains on the dye rather than on the cobalt redox mediator, enabling redox couples with higher diffusion coefficients and more suitable redox potential to be used, simultaneously improving the photocurrent and photovoltage of the device. Optimization of DSCs sensitized with a triphenylamine-based organic dye in combination with tris(2,2'-bipyridyl)cobalt(II/III) yielded solar cells with overall conversion efficiencies of 6.7% and open-circuit potentials of more than 0.9 V under 1000 W m-2 AM1.5 G illumination. Excellent performance was also found under low light intensity indoor conditions. [ABSTRACT FROM AUTHOR]

A new dye, SSD1, featuring two donor/acceptor chromophores aligned in a spiro configuration with two anchoring groups separated at a distance of 10.05 Å (closely matching the distance between the adsorption sites of the anatase TiO2surface) undergoes efficient dye adherence on TiO2films. A dye-sensitized solar cell incorporating SSD1exhibited a short-circuit current of 8.9 mA cm−2, an open-circuit voltage of 0.63 V, a fill factor of 0.67, and a power conversion efficiency of 3.75%. [ABSTRACT FROM AUTHOR]

New dipolar compounds incorporating a dithieno[3,2-b:2′,3′-d]thiophene unit as the electron donor, an oligothiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. These nonarylamine type metal-free organic compounds have been successfully used as the sensitizers of dye-sensitized solar cells (DSSCs). The conversion efficiencies of the DSSCs range from 3.54 to 5.15% under AM 1.5 G irradiation. The best efficiency reached ∼70% of the ruthenium dye N719-based standard cell fabricated and measured under similar conditions. [ABSTRACT FROM AUTHOR]

Two indole-based organic dyes were conveniently prepared and well characterized. The triphenylamine or carbazole moieties were bonded to the indole group acting as a potential electron donor, which can tune the HOMO and LUMO levels of the resultant dye, and another triphenylamine or carbazole group was linked to the pyrrole ring on the nitrogen atom, which was expected to suppress the aggregation of the dye in the solid state to some degree. These two dyes were utilized as dye sensitizers in dye-sensitized solar cells and demonstrated efficient photon-to-electron conversion properties. [ABSTRACT FROM AUTHOR]

When an alkyl-functionalized metal-free organic dye (MK-2) was employed as a sensitizer, dye-sensitized TiO2solar cells (DSSCs) fabricated with an ionic liquid (IL) electrolyte showed an energy conversion efficiency of 7.6%, which was comparable to that with a volatile liquid electrolyte. This contrasts with the case of DSSCs employing conventional Ru complex sensitizer (N719), whose efficiency was decreased markedly when the electrolyte was replaced from the volatile to IL. As a result, with the IL electrolyte, the conversion efficiency with MK-2 was higher than that with N719. The result was mainly attributed to longer electron lifetime in the DSSCs with MK-2. The longer electron lifetime is remarkable because with conventional volatile electrolyte, the lifetimes with many organic dyes including MK-2 were shorter than that with N719. This high compatibility of MK-2 with the IL electrolyte shows that the molecular modification of organic dyes can overcome the both disadvantages of ILs and organic dyes, mostly originated from their high viscosity and from the short electron lifetime observed with volatile electrolyte, respectively. Long-term stability of the DSSCs with MK-2 and the ionic electrolyte was also investigated, showing the efficiency of more than 7% for 2000 h under 1 sun conditions. [ABSTRACT FROM AUTHOR]

Solid-state dye-sensitized solar cells were fabricated using an organic dye, 2-cyanoacrylic acid-4-(bis-dimethylfluoreneaniline)dithiophene (JK2), which exhibits more than 1 V open-circuit potential (Voc). To scrutinize the origin of high voltage in these cells, transient Vocdecay measurements and density functional theroy calculations of the interacting dye/semiconductor surface were performed. A negative conduction band shift was observed due to the favorable dipolar field exerted by the JK2 sensitizer to the TiO2surface, at variance with heteroleptic Ru(II)-dyes for which an opposite dipole effect was found, providing an increased Voc. [ABSTRACT FROM AUTHOR]

A series of structurally simple dipolar light-harvesting organic dyes featuring 1,3-cyclohexadiene in the aromatic π framework for dye-sensitized solar cells has been synthesized and characterized. The highest conversion efficiency of the DSSCs based on these dyes can reach up to 4.4%. [ABSTRACT FROM AUTHOR]

New metal-free dyes with a furan moiety in the conjugated spacer between the arylamine donor and the 2-cyanoacrylic acid acceptor have been synthesized, and high efficiency dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers. [ABSTRACT FROM AUTHOR]

The article describes the design and synthesis of a molar extinction organic sensitizer coded C203 with a fused dithienothiophene unit for efficient and stable dye-sensitized solar cells. According to the authors, a ~7% cell with an organic dye showing an excellent stability measured under the thermal and light-soaking dual stress was demonstrated in combination with a solvent-free ionic liquid electrolyte.