Suppress Dye Aggregation Research Articles

Structural Engineering of Organic D-A-π-A Dyes Incorporated with a Dibutyl-Fluorene Moiety for High-Performance Dye-Sensitized Solar Cells.

Structural engineering of the light-harvesting dyes employed in DSSCs (dye-sensitized solar cells) with a systematic choice of the electron-donating and -accepting groups as well as the π-bridge allows the (photo)physical properties of dyes to match the criteria needed for improving the DSSC efficiency. Herein, we report an effective approach of molecular engineering of DSSC sensitizers, aiming to gain insights on the configurational impact of the fluorenyl unit on the optoelectronic properties and photovoltaic performance of DSSCs. Five new organic dyes (GZ116, GZ126, GZ129, MA1116, and MA1118) with a D-A-π-A framework integrated with a fluorenyl moiety were designed and synthesized for DSSCs. The fluorenyl unit is configured as part of the π-spacer for the GZ series, whereas it connected on the electron-deficient quinoxaline motif for the MA series. The devices fabricated from the MA1116 sensitizer produced the best performance under standard AM 1.5 G solar conditions as well as dim-light (300-6000 lx) illumination. The devices fabricated from MA1116 displayed a PCE of 8.68% (Jsc = 15.00 mA cm-2, Voc = 0.82 V, and FF = 0.71) under 1 sun and 26.81% (Jsc = 0.93 mA cm-2, Voc = 0.68 V, and FF = 0.76) under 6000 lx illumination. The device efficiency based on dye MA1116 under 1 sun outperformed that based on the standard N719 dye, whereas a comparable performance between devices based on MA1116 and N719 was achieved under dim-light conditions. A combination of enhancing the charge separation, suppressing dye aggregation, and providing better insulation that prevents the oxidized redox mediator from approaching the TiO2 surface all contribute to the superior performance of DSSCs fabricated based on these light-harvesting dyes. The judicious integration of the fluorenyl unit in a D-A-π-A-based DSSC would be a promising strategy to boost the device performance.

Optimization of porphyrin dyes with a bulky triphenylamine donor for developing efficient dye-sensitized solar cells

To fabricate efficient dye-sensitized solar cells (DSSCs), three porphyrin dyes XW65−XW67 have been designed and synthesized using a bulky triphenylamine donor. Based on our previously reported dyes with a carbazole donor, a bulky triphenylamine unit was employed as the donor to synthesize XW65 with the aim to enhance the electron donating ability and suppress dye aggregation. As a result, XW65 shows enhanced photocurrent density (Jsc) and open circuit voltage (Voc), affording a high efficiency of 9.02%. On this basis, XW66 was synthesized with a methyl group introduced into the carboxyphenyl acceptor to further suppress dye aggregation and improve the Voc, achieving an enhanced efficiency of 9.23% with improved Voc of 849 mV and Jsc of 14.87 mA cm−2, which can be ascribed to the further suppressed dye aggregation and enhanced adsorption amount on the TiO2 film induced by the additional methyl group. To further improve the Jsc, a benzothiadiazole (BTD) unit has been introduced as the auxiliary acceptor to afford XW67, which exhibits a strikingly red-shifted monochromatic photon-to-electron conversion efficiency (IPCE) onset wavelength of 830 nm, obtaining the highest Jsc value of 15.83 mA cm−2 among the three dyes. Consequently, despite the sacrifice of Voc caused by the severe dye aggregation associated the extended conjugation framework, XW67 exhibits the highest efficiency of 9.43%. On this basis, cosensitization with WS-5 afforded elevated efficiencies of 10.07%, 10.38% and 10.13% for XW65−XW67, respectively, owing to the simultaneously enhanced Jsc and Voc. These results indicate that it is effective to develop efficient DSSCs based on cosensitization of optimized porphyrin dyes containing a bulky triphenylamine donor, a methyl group on the carboxyphenyl acceptor, and an auxiliary electron acceptor.

Solar cells sensitized with porphyrin dyes with a carbazole donor: The effects of an auxiliary benzothiadiazole acceptor and bulky substituents on the donor

Three porphyrin sensitizers XW54–XW56 containing a carbazole donor have been designed and synthesized by introducing a benzothiadiazole (BTD) unit as the auxiliary electron acceptor to extend the absorption spectra and/or bulky dihexyloxyphenyl groups into the carbazole unit to suppress dye aggregation and improve the photovoltage (Voc). The BTD unit incorporated in XW54 obviously broadens and red-shifts the absorption threshold to ca. 700 nm, as compared with that of 650 nm observed for XW1. Thus, XW54 exhibits a much broader monochromatic photon-to-electron conversion efficiency (IPCE) spectrum with an extremely red-shifted onset wavelength of 780 nm, resulting in a photocurrent density (Jsc) of 11.60 mA cm−2, higher than that of XW1. Unfortunately, the Voc value was decreased owing to the more severe dye aggregation caused by the large conjugation framework induced by the presence of the BTD unit. As a result, XW54 shows an efficiency of 6.26%, slightly higher than that of 6.11% obtained for XW1. On the other hand, with the bulky dihexyloxyphenyl donor groups introduced to XW55, a highest Voc of 860 mV was achieved, which can be ascribed to the efficient prevention of charge recombination and suppression of dye aggregation. Thus, XW55-based cells exhibit an improved efficiency of 6.60%. On the basis of XW54 and XW55, two bulky dihexyloxyphenyl groups and a BTD unit were simultaneously introduced to XW56, affording a highest efficiency of 7.03%, with the Jsc and Voc values of 12.5 mA cm−2 and 785 mV, respectively. These results compose a novel approach for developing efficient dye-sensitized solar cells (DSSCs) by simultaneously introducing bulky dihexyloxyphenyl groups and a benzothiadiazole unit, which may synergistically broaden the absorption spectra and suppress the dye aggregation, resulting in improved photocurrent and photovoltage.

Controlling aggregation using self-assembled axially coordinated pyridine-based ligands on porphyrin analogues for dye-sensitized solar cells

Porphyrin dyes are susceptible to aggregation which may cause lower short-circuit current density affecting its photoelectric conversion efficiency (PCE) in dye-sensitized solar cells. In this paper, we harness the inherent property of metallated porphyrins that it can axially coordinate with compounds containing lone-pair of electrons, such as pyridines, through the back π-bonding. The use of pyridine or bipyridine spacers to suppress aggregation in β-functionalized Zn-tetraphenylporphyrin-based dyes showed improvement of PCEs by 28% and 44% for 4-methylpyridine and 4,4′-bipyridine ligands, respectively. This clearly demonstrates the benefits of the simple but effective method in suppressing dye aggregation thereby increasing its efficiency.

Self-Assembly by Coordination with Organic Antenna Chromophores for Dye-Sensitized Solar Cells.

The development of new sensitizers and new sensitization methods is one of the important means to enhance the conversion efficiency of dye-sensitized solar cells (DSSCs); the ultimate goal is to broaden the spectral response of dyes, reduce electron recombination, and suppress dye aggregation. In this study, we have developed a series of new self-assembled dyes and applied them in DSSCs. We prepared two organic antenna chromophores S1 and S2 and coordinated them with two acceptors A1 and A2 via zinc to construct A-Zn-S series self-assembled dyes. This method is very simple and feasible and can avoid the complex synthesis steps of traditional dyes; the results show that the light-harvesting ability of devices can be improved and charge recombination can be reduced by adjusting the structures of the antenna chromophores and acceptors. The device with A2-Zn-S1 gave a power conversion efficiency of 4.25%, which was higher than those with A1-Zn-S1 (3.88%), A1-Zn-S2 (3.21%), and A2-Zn-S2 (3.52%); the main reason for this is that the different coordination combinations between the antenna chromophore and the acceptor show great differences in Voc and Jsc. The device based on A2-Zn-S1 showed a high Voc of 632 mV and a high Jsc of 9.54 mA cm-2; one reason for this is that S1 has better spectral responsiveness and another reason is that A2 has better steric resistance that effectively reduces charge recombination. Besides, IR spectra indicate that these self-assembled dyes anchored on a TiO2 surface by bicarboxyl anchoring groups are also very beneficial for improving the performance of dyes.

Unclogging electron-transporting channels via self-assembly for improving light harvesting and stability of dye-sensitized solar cells

Two nitrogen-rich heterocycle donor dyes, NP-2 and NP-3, have been strategically designed and synthesized to construct functionalized self-assembly layers. Through the formation of N⋯H hydrogen bonds between these nitrogen-rich heterocycle donors and 4-tert-butylbenzoic acid (PTBBA), the electron leak points (imine group (N)) may be plugged, thus blocking excited-state electron lateral transferring between the adsorbed dyes and electron leaking from electron-transporting channel into the electrolyte. Furthermore, the huge 3-dimensional sizes of such supramolecule sensitizers can not only suppress dye aggregation, but enhance the photoresponse capacity in visible region. Therefore, the devices based on NP-2@PTBBA and NP-3@PTBBA, which obtained by the cocktail sensitization procedures, can be improved by increasing the open-circuit photovoltage (Voc) without any loss of the short-circuit photocurrent density (Jsc) owing to the synergy effect between self-assembly and co-sensitization. Although the device based on NP-3/PTBBA via the stepwise sensitization procedure delivers lower efficiency, it can remain at 103.14% of the initial efficiency as a result of parallel increase in Jsc and Voc values. Overall, the design principles provide a clear road map of supramolecular dye-sensitized solar cells (SDSSCs) and demonstrate the potential of 1,3,5-triazine-based dyes in solar cells research.

Organic Sensitizers with Extended Conjugation Frameworks as Cosensitizers of Porphyrins for Developing Efficient Dye-Sensitized Solar Cells.

Relatively high efficiencies have been achieved for porphyrin-based dye-sensitized solar cells. For the purpose of designing efficient cosensitizers, we herein report systematically optimized dyes XC1-XC5 employing a triphenylamine donor, a benzothiadiazole moiety as the auxiliary acceptor, and a benzoic acid acceptor. One hexyl and four hexyloxy groups were introduced, and an ethynylene moiety was introduced between the donor and the auxiliary acceptor to afford XC1. To further extend the absorption wavelength, a second ethynylene moiety was introduced between the acceptor and the auxiliary acceptor to afford XC2. XC3 and XC4 were designed by introducing one and two methyl substituents, respectively, into the meta-positions of the anchoring carboxyl group. XC5 was further synthesized by inserting a cyano substituent into one of the ortho-positions of the carboxyl group with the purpose to strengthen the intramolecular charge-transfer effect and thus broaden the absorption wavelength. As expected, compared with the Jsc (14.29 mA·cm-2) of XC1, the corresponding Jsc values for XC2-XC5 were enhanced to 16.50, 16.95, 16.73, and 17.74 mA·cm-2, respectively. Moreover, XC4 exhibits the highest Voc of 770 mV owing to the presence of a maximum of seven chains, which can effectively suppress dye aggregation. As a result, compared with XC1, XC2-XC5 exhibit improved efficiencies of 8.67, 9.05, 8.78, and 9.30%, respectively. In addition, the efficiencies of XC3 and XC5 were further enhanced by cosensitizing them with our previously reported porphyrin dye XW28 under various conditions. Finally, a remarkable efficiency of 10.50% was achieved for the cells cosensitized with XC5 and XW28. These results indicate that the combination of good planarity of the extended D-π-A framework with multiple alkoxy/alkyl chains may compose an effective optimizing strategy for designing and synthesizing excellent cosensitizers for porphyrins.

Efficient Solar Cells Based on Porphyrin Dyes with Flexible Chains Attached to the Auxiliary Benzothiadiazole Acceptor: Suppression of Dye Aggregation and the Effect of Distortion.

Donor-π-acceptor-type porphyrin dyes have been widely used for the fabrication of efficient dye-sensitized solar cells (DSSCs) owing to their strong absorption in the visible region and the ease of modifying their chemical structures and photovoltaic behavior. On the basis of our previously reported efficient porphyrin dye XW11, which contains a phenothiazine-based electron donor, a π-extending ethynylene unit, and an auxiliary benzothiadiazole acceptor, we herein report the syntheses of novel porphyrin dyes XW26-XW28 by introducing one or two alkyl/alkoxy chains into the auxiliary acceptor. The introduced chains can effectively suppress dye aggregation. As a result, XW26-XW28 show excellent photovoltages of 700, 701, and 711 mV, respectively, obviously higher than 645 mV obtained for XW11. Nevertheless, the optimized structures of XW26 and XW27 exhibit severe distortion, showing large dihedral angles of 57.2° and 44.0°, respectively, between the benzothiadiazole and benzoic acid units, resulting from the steric hindrance between the benzoic acid unit and the neighboring alkyl/alkoxy chain on the benzothiadiazole unit, and thus blue-shifted absorption, decreased photocurrents. and low efficiencies of 5.19% and 6.42% were observed for XW26 and XW27, respectively. Interestingly, XW26 exhibits a more blue-shifted absorption spectrum relative to XW27, indicating that the steric hindrance of the alkyl/alkoxy chains has a more pronounced effect than the electronic effect. Different from XW26 and XW27, XW28 contains only one alkyl chain neighboring the ethynylene unit, which does not induce obvious steric hindrance with the benzoic acid unit, and thus distortion of the molecule is not seriously aggravated compared with XW11. Hence, its absorption spectrum and photocurrent are similar to those of XW11. As a result, a higher efficiency of 9.12% was achieved for XW28 because of its suppressed dye aggregation and higher photovoltage. It is worth noting that a high efficiency of 10.14% was successfully achieved for XW28 upon coadsorption with CDCA, which is also higher than the corresponding efficiency obtained for XW11. These results provide a novel approach for developing efficient porphyrin dyes by introducing chains into the suitable position of the auxiliary benzothiadiazolyl moiety to suppress dye aggregation, without seriously aggravating distortion of the dye molecules.

Flexible Filter‐Free Narrowband Photodetector with High Gain and Customized Responsive Spectrum

Conventional narrowband photodetection is enabled by coupling broadband photodetectors with complex optical filters. The recently reported charge collection narrowing, an alternative filter‐free strategy, attains very narrowband photodetection at the sacrifice of sensitivity. Herein, a new strategy is proposed to customize the responsive spectrum with high gain by using dye molecules with intrinsically versatile and narrowband absorption. The device configuration is organic dye/Zn0.9Mg0.1O nanoparticles/graphene, where the organic dye serves as the narrowband absorber, graphene serves as the fast carrier transport channel, and Zn0.9Mg0.1O nanoparticles play a triple role of enhancing dye loading, suppressing dye aggregation and blocking charge back recombination. A high responsivity of 8 × 103 A W−1 is thus obtained at a 530 nm response peak with a 60 nm full‐width at half maximum, a four orders of magnitude increase in sensitivity compared to the best narrowband photodetectors reported to date under the comparable electric field. Organic dyes with dual‐band absorption to demonstrate narrowband photodetectors with customized responsive spectrum are further implemented. The approach opens the way to the realization of efficient flexible narrowband photodetection for electronic skin and wearable electronic applications.

Twisted Fused-Ring Thiophene Organic Dye-Sensitized Solar Cells

Fused-ring thiophene compounds emerged as an important type of building blocks for organic dyes toward the dye-sensitized solar cells (DSSCs) because of their good charge transfer and light-harvesting properties. Nevertheless, some fused-ring thiophenes have a lack of desired alkyl chains or side alkyl chains, which may induce a severe charge recombination in devices. In this work, the hex-1-en-1-ylbenzene (HEYB) unit was introduced in two new fused-ring thiophene organic dyes (M60 and M59), resulting in a modest dihedral angle (∼36°) between the donor and spacer in dyes. The effect of the HEYB unit on optical, electrochemical, and photovoltaic properties has been investigated by comparing with their congeners (M42 and M58) without the HEYB unit. It is found that introduction of the HEYB unit in arylamine donor enhanced the driving force for dye regeneration and beneficial for suppressing dye aggregation as well as reducing the charge recombination. Device performance characteristics demonstrate that intr...

Studies on D-A-π-A structured porphyrin sensitizers with different additional electron-withdrawing unit

Abstract The introduction of an additional acceptor to a typical donor-π bridge-acceptor (D-π-A) type porphyrin sensitizer results in a D-A-π-A featured porphyrin. Two porphyrins containing an additional acceptor with different electron-withdrawing abilities such as 2,3-diphenylquinoxaline ( DPQ ) for LP-11 and 2,1,3-benzothiadiazole ( BTD ) for LP-12 between the porphyrin core and the anchoring group have been synthesized for use as sensitizers in dye-sensitized solar cells (DSCs). Compared to LP-11 , LP-12 with the stronger electron-withdrawing additional acceptor BTD possesses better light harvesting properties with regard to red-shifted Q-band absorption and a broader IPCE spectrum, resulting in a greater short circuit photocurrent density ( J sc ) output. Interestingly, the steric hindrance of the DPQ group is favorable for suppressing dye aggregation, leading to a larger open-circuit voltage ( V oc ) value for LP-11 -based cell. However, the loss in V oc of LP-12 is overcompensated by an improvement in J sc . The optimized cell based on LP-12 achieves the better performance with a J sc of 15.51 mA cm −2 , a V oc of 674 mV, a fill factor (FF) of 0.7 and an overall power conversion efficiency (PCE) of 7.37% under standard AM 1.5 G irradiation. The findings provide a guidance for the future molecular design of highly efficient porphyrin sensitizers for use in DSCs.

Organic sensitizers with different thiophene units as conjugated bridges: molecular engineering and photovoltaics

Three structural modifications with incorporation of alkyl, alkoxy and vinyl bond into the skeleton of thiophene bridge in D-π-A featured organic sensitizers are specifically developed for insight into their influences on photophysical, electrochemical as well as photovoltaic properties in nanocrystalline TiO2-based dye sensitized solar cells (DSSCs). The insertion of vinyl bond into the conjugation bridge leads to the molecular planar configuration, and the conjugation bridge of 3,4-ethylenedioxythiophene (EDOT) is prone to positively shift its highest occupied molecular orbital (HOMO). The electrochemical impedance spectroscopy (EIS) results indicate that the grafted long alkyl chain onto thiophene is favorable to suppress dye aggregation when adsorbed onto TiO2 film and modification on interface of TiO2/dye/electrolyte, resulting in a relatively high open-circuit voltage (V oc). Under optimized conditions, dye LS-4 bearing hexylthiophene as the conjugation bridge shows a relatively high overall conversion efficiency of 5.45%, with a photocurrent of 11.61 mA cm–2, V oc of 744 mV.

Post-assembly atomic layer deposition of ultrathin metal-oxide coatings enhances the performance of an organic dye-sensitized solar cell by suppressing dye aggregation.

Dye aggregation and concomitant reduction of dye excited-state lifetimes and electron-injection yields constitute a significant mechanism for diminution of light-to-electrical energy conversion efficiencies in many dye-sensitized solar cells (DSCs). For TiO2-based DSCs prepared with an archetypal donor-acceptor organic dye, (E)-2-cyano-3-(5'-(5''-(p-(diphenylamino)phenyl)-thiophen-2''-yl)thiophen-2'-yl)acrylic acid (OrgD), we find, in part via ultrafast spectroscopy measurements, that postdye-adsorption atomic layer deposition (ALD) of ultrathin layers of either TiO2 or Al2O3 effectively reverses residual aggregation. Notably, the ALD treatment is significantly more effective than the widely used aggregation-inhibiting coadsorbent, chenodeoxycholic acid. Primarily because of reversal of OrgD aggregation, and resulting improved injection yields, ALD post-treatment engenders a 30+% increase in overall energy conversion efficiency. A secondary contributor to increased currents and efficiencies is an ALD-induced attenuation of the rate of interception of injected electrons, resulting in slightly more efficient charge collection.

The effects of the number of anchoring groups and N-substitution on the performance of phenoxazine dyes in dye-sensitized solar cells

Four novel phenoxazine-based organic sensitizers were synthesized and applied to dye-sensitized solar cells. Cyanoacrylic acid as an additional anchoring group was introduced to the phenoxazine for efficient electron extraction from the donor part, and an N-substituent was added to suppress dye aggregation. The photophysical, electrochemical and photovoltaic properties of the solar cells based on these dyes were investigated to study the effects of these substituents on the performance of the dye-sensitized solar cells. The additional cyanoacrylic acid acceptor improved the short-circuit current because it widened the absorption ranges of the dyes, although it also increased the recombination rate. The N-methoxyphenyl unit decrease charge recombinations, resulting in higher open-circuit voltage. However, the bulky substituent decreased the amount of dye absorbed on the TiO2. As a result, the fabricated cells with the four dyes exhibited similar overall conversion efficiencies and, of these cells, the solar cell based on the N-4-methoxyphenyl mono-cyanoacrylate substituted dye showed the highest conversion efficiency of 5.09% (short-circuit current = 10.11 mA/cm2, open-circuit voltage = 690 mV, fill factor = 72.23%, an overall conversion efficiency = 5.09% under AM 1.5G conditions).

Synthesis and Optical Properties of Water‐Soluble Polyglycerol‐Dendronized Rylene Bisimide Dyes

Four new water-soluble polyglycerol-dendronized perylene, terrylene, and quaterrylene bisimides have been synthesized and characterized with respect to their optical properties in polar organic solvents and water by using UV/Vis and fluorescence spectroscopy. All of these dyes were highly soluble in water, but the size of the chosen polyglycerol dendron was only sufficient to completely suppress dye aggregation for the core-unsubstituted perylene derivative. Their high solubility in water and their absorption and emission wavelengths up to the NIR region make the core-unsubstituted perylene and terrylene bisimides ideal candidates for applications in bioimaging, whilst the lack of fluorescence for quaterrylene bisimide in all polar solvents does not warrant further investigation of this chromophore in fluorescence and imaging applications. Likewise, tuning of the emission of rylene bisimides towards longer wavelengths by employing electron-donating bay substituents is not a promising strategy, owing to the lower fluorescence quantum yields in polar solvents and, in particular, in water.

Bulky dendritic triarylamine-based organic dyes for efficient co-adsorbent-free dye-sensitized solar cells

Three new organic photosensitizers (HK1–HK3) incorporating functionalized bulky trimer of triarylamine derivatives as the electron donor units, 3,4-ethylenedioxythiophene moiety as the conjugated spacer, and cyanoacrylic acid as the electron acceptor, have been synthesized and the effects of different bulky electron donor substituents on the photovoltaic performances of dye-sensitized solar cells (DSSCs) are investigated accordingly. The DSSC based on HK1 with tris(triphenylamine) electron donor in the absence of the co-adsorbent chenodeoxycholic acid (CDCA) shows the best photovoltaic performance under standard global AM 1.5 sunlight: a short-circuit current density (Jsc) of 10.41 mA cm−2, an open-circuit voltage of 0.76 V and a fill factor of 0.65, corresponding to a maximum overall power conversion efficiency (PCE) of 5.11%. However, in the presence of co-adsorbent CDCA, the PCEs of DSSCs based on these photosensitizers, decrease significantly by about 9.7%, which is contrary to the conventional concept that CDCA can improve the efficiency by inhibition of dye aggregation and intermolecular electron recombination. The results demonstrate that the synthesized new organic dyes with bulky dendritic triarylamine and its derivatives as electron-donation units can efficiently suppress dye aggregation without the need of the co-adsorbent and effectively reduce the intramolecular electron recombination in DSSCs.

The effect of N-substitution and ethylthio substitution on the performance of phenothiazine donors in dye-sensitized solar cells

Three new organic sensitizers with phenothiazine chromophores were synthesized and used in dye-sensitized solar cells. N-substituents were added to the phenothiazine to suppress dye aggregation and an ethylthiol was added as an additional donor function. The effects of these substituents on the performance of the dyes were investigated by assessing the photophysical, electrochemical, and photovoltaic properties. The introduction of an N-methoxyphenyl unit improved the open-circuit voltage; the addition of the ethylthiol unit decreased the amount of dye adsorbed on the TiO2. A very high open-circuit voltage of 818.5 mV was achieved by the phenothiazine with added N-methoxyphenyl and ethylthiol groups. However, the best overall conversion efficiency was achieved by a cell fabricated with a phenothiazine devoid of the ethylthiol group (an overall conversion efficiency = 6.02%, short-circuit current = 10.20 mA/cm2, open-circuit voltage = 781.7 mV, fill factor = 75.50% under AM 1.5G conditions) due to the high open-circuit voltage and greater dye adsorption.

Synthesis and Electrochemical Properties of 2,6-Bis(quinoline-2-yl)pyridyl Ruthenium Complexes as Near-Infrared Sensitizers for Dye-Sensitized Solar Cells

New ruthenium(II)–polypyridyl complexes 1a–1d (1a: X= Y= H, 1b: X= H, Y= Cl, 1c: X= H, Y= Me, 1d: X= COOH, Y= H) having 2,6-bis(4-carboxyquinolin-2-yl)pyridine derivatives as ligands were synthesized as sensitizers for dye-sensitized solar cells (DSCs) and their photophysical and photochemical properties were characterized. The photovoltaic performance of DSCs sensitized with 1a–1d was found to be different. The DSC sensitized with 1a exhibits higher efficiency and IPCE value than those sensitized with 1b–1d. The APCE value of the DSC sensitized with 1a was almost 80% in the 500–800 nm range. Therefore, the performance of the DSC sensitized with 1a might improve if the adsorption of 1a on the TiO2 surface could be appropriately controlled by investigation of dye immersion condition or introduction of bulky substituents on the ligand in order to suppress dye aggregation.

Synthesis and Electrochemical Properties of 2,6-Bis(quinoline-2-yl)pyridyl Ruthenium Complexes as Near-Infrared Sensitizers for Dye-Sensitized Solar Cells

New ruthenium(II)–polypyridyl complexes 1a–1d (1a: X= Y= H, 1b: X= H, Y= Cl, 1c: X= H, Y= Me, 1d: X= COOH, Y= H) having 2,6-bis(4-carboxyquinolin-2-yl)pyridine derivatives as ligands were synthesized as sensitizers for dye-sensitized solar cells (DSCs) and their photophysical and photochemical properties were characterized. The photovoltaic performance of DSCs sensitized with 1a–1d was found to be different. The DSC sensitized with 1a exhibits higher efficiency and IPCE value than those sensitized with 1b–1d. The APCE value of the DSC sensitized with 1a was almost 80% in the 500–800 nm range. Therefore, the performance of the DSC sensitized with 1a might improve if the adsorption of 1a on the TiO2 surface could be appropriately controlled by investigation of dye immersion condition or introduction of bulky substituents on the ligand in order to suppress dye aggregation.

Organic Dyes Incorporating Bis-hexapropyltruxeneamino Moiety for Efficient Dye-Sensitized Solar Cells

We report here on the synthesis and photophysical/electrochemical properties of three functional triarylamine organic dyes (MXD5−7) as well as their application in dye-sensitized nanocrystalline TiO2 solar cells (DSSCs). For the designed dyes, the nonplanar structures of bis-hexapropyltruxeneamino take the role of electron donor. The introduction of bis-hexapropyltruxeneamino units brought about superior performance over the simple triphenylamine dye, in terms of light-capturing abilities and suppressing dye aggregation. Among three dyes, the DSSCs based on the dye MXD7 showed the best photovoltaic performance: a short-circuit photocurrent density (JSC) of 11.8 mA cm−2, an open-circuit photovoltage (VOC) of 772 mV, and a fill factor (ff) of 0.68, corresponding to an overall conversion efficiency of 6.18% under 100 mW cm−2 irradiation. These dyes exhibited high VOC values, possible origin for which was investigated regarding the TiO2 surface blocking, conduction band movement, and electrolyte-dye interaction.