Triphenylamine Dyes Research Articles

Spatially Resolved Analysis of Screen Printed Photoanodes of Dye-Sensitized Solar Cells by Scanning Electrochemical Microscopy

Different approaches are compared for imaging local differences in the performance of nanostructured dye-sensitized solar cells (DSCs) using scanning electrochemical microscopy (SECM). The DSCs were fabricated from TiO2 and the triphenylamine dye (E)-3-(5-(4-(bis(2',4'-dibutoxy-[1,1'-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid, called D35. The components of the redox electrolytes cobalt trisbipyridine ([Co(bpy)3]3+/2+) and iodide/triiodide (I‐/I3−) were used as SECM mediators. Imaging was performed by the feedback (FB) mode and the substrate-generation/tip collection (SG/TC) mode of SECM with additional options of local and temporal illumination. In FB mode, the SECM microelectrode (ME) reduces the mediator which is re-oxidized at the illuminated photoanode. In the SG/TC mode, the reduced form of the mediator is oxidized at the photoanode and the oxidized form is detected at the ME. It is expected that the SG/TC is more sensitive than the FB mode but provides lower lateral resolution. However, imaging is complicated by the strong light scattering in the nanoporous photoanode and the long residence time of charge carriers under the conditions of SECM imaging with low mediator concentrations. This prevents approaches based on local illumination or temporal illumination. Using shear force SECM (SF-SECM) in the FB mode, local differences in the morphology and performance of screen-printed photoanodes could be resolved that resulted from screen printing process. The morphological variations are also corroborated by scanning force microscopy and optical phase contrast microscopy. Furthermore, isolated irregularities were detected in which morphology and local performance were not correlated.

A Strategy for Enhancing the Performance of Borondipyrromethene Dye-Sensitized Solar Cells

Borondipyrromethene (BODIPY) dyes are one of the most interesting organic dyes because of their unique characteristic in capturing near-infrared (NIR) solar radiation. However, the highest reported conversion efficiency of BODIPY dyes is still far behind that of other organic dyes. Herein, we demonstrated an efficient strategy for enhancing the photovoltaic performance of BODIPY dyes, i.e., introducing a long linker between the light harvesting antenna and acceptor. Interestingly, the linker length has opposite effects on the BODIPY (M62, M63, M66, and LB1) and triphenylamine (M64 and M65) dyes. This work suggests that the incorporated long linker in BODIPY dyes shows several favorable characteristics: (i) improving the light harvesting capability of BODIPY dyes in longer wavelength without a big change of the HOMO levels; (ii) efficiently increasing the photocurrent and photovoltage, leading to dramatically improved performance; (iii) significantly reducing the charge recombination between electrons in T...

Bi‐anchoring Organic Dyes that Contain Benzimidazole Branches for Dye‐Sensitized Solar Cells: Effects of π Spacer and Peripheral Donor Groups

Benzimidazole-branched bi-anchoring organic dyes that contained triphenylamine/phenothiazine donors, 2-cyanoacrylic acid acceptors, and various π linkers were synthesized and examined as sensitizers for dye-sensitized solar cells. The structure-activity relationships in these dyes were systematically investigated by using absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The wavelength of the absorption peak was more-heavily influenced by the nature of the π linker than by the nature of the donor. For a given donor, the absorption maximum (λmax ) was red-shifted on changing the π linker from phenyl to 2,2'-bithiophene, whilst the dyes that contained triphenylamine units displayed higher molar extinction coefficients (ϵ) than their analogous phenothiazine-based triphenylamine dyes, which led to good light-harvesting properties in the triphenylamine-based dyes. Electrochemical data for the dyes indicated that the triphenylamine-based dyes possessed relatively low-lying HOMOs, which could be beneficial for suppressing back electron transfer from the conduction band of TiO2 to the oxidized dyes, owing to facile regeneration of the oxidized dye by the electrolyte. The best performance in the DSSCs was observed for a dye that possessed a triphenylamine donor and 2,2'-bithiophene π linkers. Electron impedance spectroscopy (EIS) studies revealed that the use of triphenylamine as the donor and phenyl or 2,2'-bithiophene as the π linkers was beneficial for disrupting the dark current and charge-recombination kinetics, which led to a long electron lifetime of the injected electrons in the conduction band of TiO2 .

Flexible amine-functionalized triphenylamine derivative as a fluorescent “light-up” probe for G-quadruplex DNA

In this study, a flexible amine-functionalized triphenylamine dye 2 was developed and utilized as a G4 DNA fluorescent probe. The selectivity, sensitivity and binding properties of the dye 2 interacting with G4 DNAs were investigated. The dye 2 illustrated in the fluorescence titration assays were preferentially bound with G4 DNAs with significant “light-up” effect. The detection limit value of 2 for the G4 DNA was below 10 nM in solution. CD spectroscopy analysis revealed that 2 could promote the G-rich sequence to adapt an antiparallel G4 structure. These results indicated the dye 2 showed stronger binding affinity and fluorescence response to G4 DNA than our previous reported triphenylamine-quinolinium scaffold (1b) due to the incorporation of a flexible amine moiety. Therefore, this study gave certain crucial factors on developing of effective fluorescence probes for G4 DNA. The cellular application of 2 in cancer cells HepG2 was also demonstrated.

Triphenylamine-based tri-anchoring organic dye with enhanced electron lifetime and long-term stability for dye sensitized solar cells

An organic sensitizer with a multi-anchoring system is a versatile methodology for enhancing the stability and conversion efficiency of dye-sensitized solar cells (DSSCs). Triphenylamine dyes (TPA3T1A∼3A) containing different numbers of anchoring groups are synthesized to determine the correlation between the number of anchoring groups and photovoltaic properties as photosensitizers for DSSCs. The adsorption properties of the dyes on TiO2 electrode were examined by ATR-FT-IR, which show that a mono-anchoring TPA3T1A system adsorbs in monodentate ester-type mode, and the three carboxylic acids in TPA3T3A adsorbs in bidentate bridging mode. The multi-anchoring dye exhibits strong electronic coupling with TiO2, providing an efficient charge injection rate. Moreover, they increased the electron lifetime significantly by suppressing the charge recombination probability. This synergistic effect enables the fabrication of efficient photovoltaic devices. Furthermore, enhanced long-term stability is also observed in the DSSCs containing a tri-anchoring system compared to the mono- and bi-anchoring systems.

Structural Effects of the Donor Moiety on Reduction Kinetics of Oxidized Dye in Dye-Sensitized Solar Cells

One of the major factors influencing the regeneration rate of the oxidized dye in dye-sensitized solar cells (DSSCs) is the energy difference (ΔG) between the levels of the dye’s HOMO and redox couple in the electrolyte. To investigate other factors that influence this process, we examined the effect of structural differences of donor moieties on the reduction rate of the oxidized dye of organic dyes that is composed of an acceptor unit, a π-conjugated linker unit, and a donor unit, including carbazole dye (MK-1), triphenylamine dye (MK-88), and coumarin dye (MK-31). The DSSCs using MK-88 showed the fastest regeneration rate even though the ΔG was not the largest among the dye structures evaluated. The regeneration rates of all of the dyes were enhanced by reducing the number of adsorbed dyes. On the basis of the results, we attribute the fast regeneration of MK-88 to the large collision cross section of the oxidized dye, that is, the increased reduction rate to the larger exposure of the HOMO of the dyes...

Insight into the effects of modifying π-bridges on the performance of dye-sensitized solar cells containing triphenylamine dyes.

Herein we prepare four novel D-π-A dyes based on triphenylamine (ZHG1, ZHG2, ZHG3 and ZHG4) by modifying the π-bridges. Compared with ZHG1, the power conversion efficiency (PCE) of ZHG2 is improved to 6.1% after the introduction of ethynyl. But further extension of the conjugation of the π-bridges by introducing the chromophore 4,8-bis(n-octyloxy)-benzo[1,2-b:4,5-b']dithiophene (BDT) into ZHG3 conversely decreases the PCE to 4.6%. Improving the coplanarity by replacing cyclobenzene with thiophene in ZHG4 after introducing BDT further decreases the PCE of ZHG4 to 4.3%. Theoretical calculations indicate that the LUMOs of ZHG3 and ZHG4 were mainly delocalized over benzothiadiazole which is far from the anchoring groups. Cyclic voltammetry experiments indicate that the LUMO energy levels of ZHG3 and ZHG4 are lower than those of ZHG1 and ZHG2. Both of these results affect the ability to inject electrons into the TiO2 conduction band. X-ray photoelectron spectroscopy (XPS) analysis shows that the mean thickness of the dye coverage for ZHG1, ZHG2, ZHG3 and ZHG4 is 16 Å, 18 Å, 27 Å and 24 Å, respectively. So the tilt angle of the dye backbone anchored on the TiO2 film is in the order of ZHG1 > ZHG2 > ZHG4 > ZHG3, which is consistent with the dye coverage of the outermost TiO2 surfaces. This result indicates that the intermolecular π-π aggregation in ZHG3 and ZHG4 with overlong π-bridges is more serious compared with that in ZHG1 and ZHG2. Perhaps the above two factors are the reason that the PCEs of ZHG3 and ZHG4 are lower than those of ZHG1 and ZHG2. So it is very important to find a balance point between the electron injection ability, intermolecular π-π aggregation and the expansion of the light absorption range.

Dual donor–π–acceptor type organic dyes for efficient dye-sensitized solar cells

A dual-styrene-π-linked triphenylamine dye was synthesized, showing effective improvement in the efficiency of the corresponding devices as compared to no π-linker dyes.

Non-linear Optical Response of Triphenylamine Dyes with D-A-π-A Structure

Non-linear Optical Response of Triphenylamine Dyes with D-A-π-A Structure

Enhancement of dye regeneration kinetics in dichromophoric porphyrin-carbazole triphenylamine dyes influenced by more exposed radical cation orbitals.

Reduction kinetics of oxidized dyes absorbed on semiconductor surfaces and immersed in redox active electrolytes has been mainly modeled based on the free energy difference between the oxidation potential of the dye and the redox potential of the electrolyte. Only a few mechanisms have been demonstrated to enhance the kinetics by other means. In this work, the rate constant of the reduction of oxidized porphyrin dye is enhanced by attaching non-conjugated carbazole triphenylamine moiety using iodine/triiodide and tris(2,2'-bispyridinium)cobalt II/III electrolytes. These results are obtained using transient absorption spectroscopy by selectively probing the regeneration kinetics at the porphyrin radical cation and the carbazole triphenylamine radical cation absorption wavelengths. The enhancement in the reduction kinetics is not attributed to changes in the driving force, but to the more exposed dye cation radical orbitals of the dichromophoric dye. The results are important for the development of high efficiency photo-electrochemical devices with minimalized energy loss at electron transfer interfaces.

Dye mixture promoted light harvesting for organic dye-sensitized solar cells using triphenylamine dyes with various numbers of anchoring groups

Co-sensitizers and co-adsorbents are promising materials to enhance the light harvesting efficiency and reduce the un-expected back transfer reaction (recombination) of dye-sensitized solar cells (DSSCs). In this study, three sensitizers with triphenylamine as an electron donor, thiophene as a bridge and various numbers of acceptors/anchors cyanoacetic acid (TPA3T1A, TPA3T2A and TPA3T3A) were synthesized, and TPA3T1A and TPA3T2A were used as co-adsorbents with TPA3T3A. The results showed that co-adsorption on the TiO2 surface at the following percentages, TPA3T3A 73%, TPA3T1A 17% and TPA3T2A 10%, resulted in an increase in the photovoltaic performance of the DSSCs from 5.27% to 5.83% compared to that of a single TPA3T3A sensitizer due to the increasing JSC and VOC. This enhancement might be due to improved light absorption and decreasing recombination by the co-sensitizers, TPA3T1A and TPA3T2A, occupying all the empty plases on the TPA3T3A-adsorbed TiO2 surface.

Effect of recombination and binding properties on the performance of dye sensitized solar cells based on propeller shaped triphenylamine dyes with multiple binding groups

Herein we report three novel donor-π-acceptor type dyes TPAA1, TPAA2 and TPAA3, which were investigated for photophysical and electrochemical properties as well as dye-sensitized solar cell performance. These dyes have triphenylamine group at the core of the structure acting as the donor moiety which is radially connected to one, two or three cyanoacrylic acid acceptor groups through phenylethynyl bridges. These dyes can harvest light up to 600nm as revealed by absorption studies, which is complemented by the IPCE spectra. The propeller shapes of the dyes prevent their aggregation on TiO2 surface and give better solar cell performance without the need for any co-adsorbent. DSSCs fabricated using TPAA1 gave the best solar cell performance with a short circuit current (Jsc) of 9.96mAcm−2, an open circuit voltage (Voc) of 0.69V and a fill factor (FF) of 0.73, which correspond to an overall power conversion efficiency of 5.05%. Infrared spectroscopy and computational studies were carried out which gave interesting insights into the mode of dye binding to TiO2. Lifetime and recombination measurements were carried out using charge extraction and detailed impedance analysis. The Nyquist and Bode plots along with the fitted EIS data reveal that resistance to recombination is higher for TPAA1 in comparison to TPAA2 and TPAA3 leading to better cell performance, which in turn may be attributed to the orientation of the dye molecule on the TiO2 surface.

First Principle Study of Electronic and Non-Linear Optical (NLO) Properties of Triphenylamine Dyes: Interactive Design Computation of New NLO Compounds

In this study, density functional theory and time-dependent density functional theory are used to determine how the size of π-conjugated system influences the absorption spectra and non-linear optical (NLO) properties of dyes. Double and triple bonds, as well the benzene rings, are used in conjugated systems. The results of the theoretical computation show that the absorption spectra are gradually broadened and red-shifted with increases in the conjugation length. Theoretical examination of the NLO properties was performed on the key parameters of polarizability and hyperpolarizability. A notable increase in the non-linear optical response was observed with an increase in the conjugation length of the π-spacer.

Computational Designing of Triphenylamine Dyes with Broad and Red‐shifted Absorption Spectra for Dye‐sensitized Solar Cells using Multi‐Thiophene Rings in π‐Spacer

In this paper, we present the design of five new derivatives of triphenylamine dyes with variable thiophene rings (0–5) and shed light on their electrooptical and charge‐injection properties. Computational techniques are used to study the effect of the thiophene moieties on the properties of interest, i.e., how the number of thiophene rings in π‐conjugated systems influence the absorption spectra and electron injection of the dyes. The results show that the absorption spectra gradually became broad and red‐shifted (384–542 nm) with the number of thiophene units. The effect of thiophene units on the performance of sensitizers in dye‐sensitized solar cells is also determined. During theoretical examination, the electron injection efficiency (Φinject) and light harvesting efficiency (LHE) are determined. Results indicate that the selection of appropriate lengths of conjugated bridges in the dye sensitizer is very important in designing high‐efficiency dyes.

Influence of Dye Architecture of Triphenylamine Based Organic Dyes on the Kinetics in Dye-Sensitized Solar Cells

The impact of the dye architecture on the kinetics in the dye-sensitized solar cell (DSC) was investigated for two structurally similar organic dyes, adsorbed to a mesoporous TiO2 film. Differences in the HOMO and LUMO levels of the triphenylamine dyes D35 and D45 were negligible, indicating that the changes in kinetics of the electron transfer processes in the solar cells can be attributed to structural differences of the organic dyes. The electron transfer kinetics of various processes was investigated by scanning electrochemical microscopy (SECM), transient absorption spectroscopy (TAS), and impedance spectroscopy (IS). SECM was used for the first time to determine the rate constants of the regeneration (reduction) of a photooxidized organic dye by a one-electron cobalt mediator. Both TAS and IS measurements showed differences in recombination of electrons in TiO2 with oxidized D35 and D45. D45 with its shorter dimethoxyphenyl units yielded faster recombination and regeneration than D35, as measured by...

Broadband transient absorption spectroscopy with 1- and 2-photon excitations: Relaxation paths and cross sections of a triphenylamine dye in solution.

1-photon (382 nm) and 2-photon (752 nm) excitations to the S1 state are applied to record and compare transient absorption spectra of a push-pull triphenylamine (TrP) dye in solution. After 1-photon excitation, ultrafast vibrational and structural molecular relaxations are detected on a 0.1 ps time scale in nonpolar hexane, while in polar acetonitrile, the spectral evolution is dominated by dipolar solvation. Upon 2-photon excitation, transient spectra in hexane reveal an unexpected growth of stimulated emission (SE) and excited-state absorption (ESA) bands. The behavior is explained by strong population transfer S1 → Sn due to resonant absorption of a third pump photon. Subsequent Sn → S1 internal conversion (with τ1 = 1 ps) prepares a very hot S1 state which cools down with τ2 = 13 ps. The pump pulse energy dependence proves the 2-photon origin of the bleach signal. At the same time, SE and ESA are strongly affected by higher-order pump absorptions that should be taken into account in nonlinear fluorescence applications. The 2-photon excitation cross sections σ(2) = 32 ⋅ 10(-50) cm(4) s at 752 nm are evaluated from the bleach signal.

The effect of cyclic thiourea functionalization and β,β′-dialkylbithiophene linker on the performance of triphenylamine dyes

Four new dyes (T-C1, T-C6, S-C1 and S-C6) with β,β′-dialkylbithiophene as π-linkers were synthesized and utilized in dye-sensitized solar cells (DSSCs). Compared with the reference dyes (T-C0 and AZ6) with bithiophene as π-linkers, these dyes show blue-shifted absorption bands, and their DSSCs produce lower short-circuit current and high open-circuit voltage. These may be caused by the increase of dihedral angle between two thiophenes. On the one hand, the molecular conjugations are decreased; on the other hand, steric effect of the whole structures are increased. Compared with the triphenylamine dyes (T-C0, T-C1 and T-C6), the cyclic thiourea functionalized dyes (AZ6, S-C1 and S-C6) exhibit better photophysical and photovoltaic performances. However, the superiority of cyclic thiourea functionalization is gradually disappearing with the increased steric effect of the π-linkers.

Novel organic dyes based on diarylmethylene-bridged triphenylamine for dye-sensitized solar cells

Three D–π–A type organic dyes, including TB-1, TTB-1 and TTB-2, which contained bridged triphenylamine (TPA) donor moieties, were synthesized and characterized for applications in dye-sensitized solar cells (DSSCs). Compared to TB-1, the 5-hexyl and 3-hexyl substituted thiophene rings were introduced onto the TPA core in TTB-1 and TTB-2. Their photophysical, electrochemical and photovoltaic properties were investigated. The reference compound L1 (the triphenylamine counterpart of TB-1) was also evaluated for comparison. Compared to L1, the bridged triphenylamine based dyes studied showed enhanced performances, suggesting reasonable design of the new dyes. Meanwhile, the investigation of the three bridged TPA dyes demonstrated that by grafting 5-hexyl substituted thiophene onto the bridged TPA, TTB-1 had a significantly broader absorption spectrum in the UV–vis region, and thereby, its light harvesting ability was remarkably enhanced. Accordingly, the higher incident photon to current conversion efficiency (IPCE) of TTB-1 indicated a higher short-circuit current. In contrast, the 3-hexyl substituted thiophene in TTB-2 lead to larger steric hindrance, resulting in lower Jsc value. Similar structure of TTB-1 and TTB-2 afforded almost the same Voc. Therefore, dye TTB-1 showed the best performance, exhibiting power conversion efficiency of 4.35%, with Jsc of 8.61mAcm−2 and Voc of 704mV under simulated AM 1.5 irradiation (100mWcm−2).

Fabrication of dye sensitized solar cells with different anchoring mode based triphenylamine dyes

Two new organic sensitizers of type D-π-A (Donor-π-Acceptor) and D-(π-A)2 were designed and synthesized to understand the effect of anchoring mode towards TiO2 film which leads to influence the efficiency of the fabricated dye sensitized solar cells. These dyes were synthesized based on the triphenylamine as electron donor, phenylhydrazine as π-conjugated spacer and 4-iodobenzoic acid as anchoring/acceptor group and characterized by 1H, 13C NMR and mass spectroscopy studies. The optical absorption of sensitizers shows red shift as well as high molar extinction co-efficient with extension of the π-conjugation and the quantum chemical calculation studies were performed to provide sufficient driving force for electron injection into conduction band of TiO2. The DSSC based on type D-(π-A)2 shows power conversion efficiency (PCE = η) 1.07% under simulated AM 1.5 G; due to more positive HOMO values, higher IPCE values, high adsorption capacity on TiO2 as well as longer electron life time of dye.

Multichromophoric di-anchoring sensitizers incorporating a ruthenium complex and an organic triphenyl amine dye for efficient dye-sensitized solar cells

A metal–organic combinatorial dye comprised of a ruthenium complex and an organic triphenyl amine dyad has been constructed.