Groups For Dye-sensitized Solar Cells Research Articles

Efficient organic sensitizers with pyridine-N-oxide as an anchor group for dye-sensitized solar cells.

Five organic dyes with pyridine-N-oxide as the anchor group and electron acceptor have been synthesized and applied in dye-sensitized solar cells (DSSCs). Benzothiadiazole was introduced in the conjugation system to increase the electron withdrawing properties, FTIR spectra showed that the coordination was between the pyridine-N-oxide and the Brønsted acid site on the TiO2 surface. The relationship between different dye structures and the performance of the DSSCs was investigated systematically. The location of the thiophene unit was studied, and the direct linkage of benzothiadiazole with pyridine-N-oxide was beneficial to broaden the absorption. The donor-acceptor-acceptor-configured dye WL307, which has 2-ethylhexyloxy chains in the donor part, showed the best efficiency of 6.08% under 100 mW cm(-2) light illumination. The dye series showed a fairly good stability during the one month test period.

DCM-based organic dyes with electron donating groups for dye-sensitized solar cells.

Herein, 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM)-based dyes with electron donating groups were designed and their electronic and optical properties were investigated theoretically for dye-sensitized solar cells (DSSCs). Among the dyes, the D1 and D2 dyes were composed of single electron donating group and the D3 and D4 dyes composed of dual donating group. We performed DFT/TDDFT calculations to get insight into the factors responsible for photovoltaic properties as dye sensitizers. It showed that all the dyes in this work are available as dye sensitizers from the energy consideration compared to TiO2 electrode and iodide electrolyte. It also showed that the D3 and D4 dyes produced additional absorption bands by the introduction of dual donor in absorption spectra and the absorption band of the D4 dye is more red-shifted than that of the D3 dye. It is attributed to the fact that the M2 (a coumarin derivative) moiety with stronger electron withdrawing ability stabilized its LUMO level. In terms of molar extinction coefficient and panchromatic feature, we suggest that the D4 dye would show better performance than other dyes in the present study as a dye sensitizer for DSSCs.

Development of D–π–A dyes with a pyrazine ring as an electron-withdrawing anchoring group for dye-sensitized solar cells

D–π–A and (D–π–)2A fluorescent dyes (OUK-1 and OUK-2) with a pyrazine ring as an electron-withdrawing anchoring group capable of forming a hydrogen bond or a pyrazinium ion at the Bronsted acid sites on TiO2 surface have been developed as a new type of D–π–A dye sensitizer for dye-sensitized solar cells.

Molecular Engineering of 2-Quinolinone Based Anchoring Groups for Dye-Sensitized Solar Cells

Six new donor−π spacer–acceptor (D-π-A) organic sensitizers based on the 2-quinolinone moiety as acceptor and anchoring groups were synthesized and tested for their performance in dye-sensitized solar cells (DSSCs). The systematic tuning of acceptor strength and anchoring modes lead to a variation of the photoelectrochemical properties and device performances. Characterization of the molecular structure and electronic and optical properties of the dyes, as well as their photovoltaic performance in DSSCs, was accomplished by means of NMR, UV spectroscopy, electrochemistry, quantum chemical, Fourier transform infrared spectroscopy, and transient photovoltage decay techniques. Thereby, significant dependence of DSSC performance on the substituents and anchoring groups was observed. In general, the optoelectronic properties of the sensitizers were mainly governed by the 2-quinolinone acceptor segment. Different types of anchoring modes were employed in this new type of acceptor segment, and their significance in the solar conversion efficiency was analyzed. Amide N,O-chelating anchoring mode and bianchor-type anchoring mode show higher short circuit current density among the various anchoring groups. This new type of anchoring mode will emerge as a promising alternative anchoring group to the widely utilized cyanoacrylic acid group.

A Novel Alkoxysilyl Azobenzene Dye Photosensitizer with Alkylamino Group for Dye-Sensitized Solar Cells

A newly designed alkoxysilyl azobenzene dye with alkylamino group, 4-diethoxyphenylsilyl-4′-dimethylaminoazobenzene, was synthesized and examined as the photosensitizer for a dye-sensitized solar cell (DSSC). The novel azobenzene dye exhibited a strong absorption band in the visible region, and the solar cell using the dye as the sensitizer showed an incident monochromatic photon-to-current conversion efficiency (IPCE) value of 66 % at 440 nm and a light-to-electric energy conversion efficiency of 2.2 % under simulated sunlight irradiation of AM-1.5G one sun condition. The energy conversion efficiency obtained here is the highest value among those reported so far for azobenzene-sensitized solar cells, indicating the potential of alkoxysilyl dyes as photosensitizers for DSSCs.

Novel design of organic donor–acceptor dyes without carboxylic acid anchoring groups for dye-sensitized solar cells

Organic donor–acceptor dyes, formed by a high-yielding [2 + 2] cycloaddition–retroelectrocyclisation process between aniline-substituted alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), were employed as novel photosensitizers without carboxylic acid anchoring groups in dye-sensitized solar cells (DSSCs). The efficient adsorption of the donor–acceptor dyes onto TiO2 was confirmed by UV-vis and IR spectroscopies. The photovoltaic performances of the DSSCs suggested that the triphenylamine derivatives 3 and 4 provide higher current densities (Jsc) as compared to the corresponding dimethylaniline counter molecules 1 and 2. This was mainly due to the excellent charge-separation efficiencies and lower charge-recombination rates of the triphenylamine moieties. It was also found that the devices sensitized by the TCNQ-adducted dyes 2 and 4 display open-circuit voltages (Voc) higher than those of the TCNE-adducted counter dyes 1 and 3. All these results were reasonably explained by the J–V curve fitting based on the equivalent-circuit model as well as the comparison between the absorption and incident-photon-to-current-conversion efficiency (IPCE) spectra.

Development of D–π–Cat fluorescent dyes with a catechol group for dye-sensitized solar cells based on dye-to-TiO2 charge transfer

D–π–Cat fluorescent dyes YM-1 and YM-2 with a diphenylamine moiety as the electron-donating group, a catechol (Cat) unit as the anchoring group and fluorene or carbazole as the π-conjugated system were designed and developed as a photosensitizer for type-II dye-sensitized solar cells (DSSCs), which have a direct electron-injection pathway from the dye to the conduction band (CB) of the TiO2 electrode by photoexcitation of the dye-to-TiO2 charge transfer (DTCT) bands. Furthermore, not only to gain insight into the influence of the molecular structure of D–π–Cat dyes on the appearance of a DTCT band and the electron-injection mechanism, but also to investigate the impacts of the DTCT characteristics of D–π–Cat dyes on the photovoltaic performances of DSSCs, a D–π–Cat fluorescent dye YM-3 with carbazole–terthiophene as the π-conjugated system was also synthesized. It was found that the D–π–Cat dyes possess a good light-harvesting efficiency (LHE) in the visible region due to a broad absorption band corresponding to DTCT upon binding to a TiO2 film. The incident photon-to-current conversion efficiency (IPCE) corresponding to the DTCT band for DSSCs based on YM-1 and YM-2 is higher than that for YM-3. This work indicates that the stabilization of the LUMO level and the expansion of the π-conjugated system by the introduction of a long π-bridge such as terthiophene on the Cat moiety can lead to an increase in the intramolecular charge transfer (ICT) excitation based on π → π* transition with a decrease in the DTCT characteristics, resulting in enhancement of an indirect electron-injection pathway from the excited dye to the CB of TiO2 by photoexcitation of the local band of the adsorbed dye on TiO2.

Organic D–π–A sensitizer with pyridinium as the acceptor group for dye-sensitized solar cells

A systematical investigation of the organic D–π–A sensitizers with different pyridiniums as acceptor group when compared to the reference dye.

Development of a D–π–A dye with benzothienopyridine as the electron-withdrawing anchoring group for dye-sensitized solar cells

A D–π–A dye SAT-1 with benzo[4,5]thieno[2,3-c]pyridine as the electron-withdrawing anchoring group capable of forming a hydrogen bond or a coordinate bond on a TiO2 surface was developed as a new-type of D–π–A dye sensitizer for dye-sensitized solar cells.

Effects of benzo-annelation of asymmetric phthalocyanine on the photovoltaic performance of dye-sensitized solar cells.

Novel highly asymmetric zinc tetraazaporphyrin (TAP) derivatives (Zn-tri-TAPNc and Zn-tri-PcNc) with one carboxyl and three tert-butyl peripheral substituent groups were synthesized. A highly asymmetric zinc phthalocyanine (ZnPc) derivative (Zn-tri-PcNc) has a benzo-annelated ring which contains tribenzonaphtho-condensed tetraazaporphyrin with the same peripheral substituents as Zn-tri-TAPNc. As a sensitizer for the TiO2-based dye-sensitized solar cell, Zn-tri-PcNc derived from the benzo-annelation of the TAP macrocycle showed improved light harvesting and electron injection efficiency, which can retard the charge recombination, resulting in a great improvement in the incident photon-to-current conversion efficiency (IPCE). The Zn-tri-PcNc-sensitized solar cell exhibited a higher conversion efficiency (2.89%) than the Zn-tri-TAPNc-sensitized one (1.20%) under AM 1.5G solar irradiation. The present results on the TAP macrocycle's benzo-annelation demonstrate that optimization of molecular structure via changing the peripheral substituent group's "push-pull" effect and enlarging the conjugated π-system is an effective approach to improve the performance of the tetraazaporphyrin-based dye-sensitized solar cell.

Ruthenium Sensitizer Functionalized by Acetylacetone Anchoring Groups for Dye-Sensitized Solar Cells

A new ruthenium sensitizer Ru-acac (cis-bis(thiocyanato)(2,2′-bipyridyl-4,4′-di(3-pentane-2,4-dione)(4,4′-dinonyl-2′-bipyridyl)ruthenium(II)) functionalized by acetylacetone (acac) anchoring groups was synthesized and studied in ZnO-based dye-sensitized solar cells (DSCs). In comparison with the parent ruthenium complex bearing classical carboxylic acid groups (coded Z907), Ru-acac exhibits blue-shifted metal-to-ligand charge transfer (MLCT) absorption and emission bands as well as a cathodic shifted oxidation potential (E(RuIII/II)). Quantum chemistry time-dependent density functional theory (TD-DFT) calculations revealed that the acac groups are less conjugated with the pyridine units than carboxylic acid groups, entailing a lower electronic coupling with the semiconductor (SC) conduction band. Finally, the photovoltaic performances of both ruthenium complexes were investigated in DSCs by recording the J/V characteristics under solar spectrum simulation (AM1.5), the photoaction spectra, and by electrochemical impedance measurements. We showed that Z907 display higher photoconversion efficiency than Ru-acac owing to a lower electronic coupling with the SC and a different bending of the conduction band. Interestingly, the acac group provides a covalent binding to the ZnO surface but does not etch the structure as carboxylic acid usually does.

Zinc Porphyrins with a Pyridine‐Ring‐Anchoring Group for Dye‐Sensitized Solar Cells

Anchoring groups are extremely important in controlling the performance of dye-sensitized solar cells (DSCs). The design and characterization of sensitizers with new anchoring groups, in particular non-carboxylic acid groups, has become a recent focus of DSC research. Herein, new donor-π-acceptor zinc-porphyrin dyes with a pyridine ring as an anchoring group have been designed and synthesized for applications in DSCs. Photophysical and electrochemical investigations demonstrated that the pyridine ring worked effectively as an anchoring group for the porphyrin sensitizers. DSCs that were based on these new porphyrins showed an overall power-conversion efficiency of about 4.0 % under full sunlight (AM 1.5G, 100 mW cm(-2)).

A new type of organic sensitizers with pyridine-N-oxide as the anchoring group for dye-sensitized solar cells

A series of organic dyes with alkaline pyridine-N-oxide as the electron acceptor and anchoring group have been synthesized and applied in dye-sensitized solar cells. Photoelectrical data show a good coordination between pyridine-N-oxide and TiO2 films, which effectively guarantee the injection and adsorption of the dye molecules. With the simple WL102 dye, the best photon-to-electron conversion efficiency of 3.72% and an excellent IPCE value about 95% have been achieved under optimized conditions.

Highly efficient iso-quinoline cationic organic dyes without vinyl groups for dye-sensitized solar cells

Four organic dyes without a vinyl group are synthesized and applied in dye-sensitized solar cells (DSSCs). The iso-quinoline cation is employed firstly as an electron acceptor in the dye molecular structure. The effect of different dye structures on the photo-electrochemical properties and the performance of the DSSCs are systematically studied. The photovoltaic performances of the DSSCs sensitized by the JH304 dye exhibit the best conversion efficiency of 7.3% (under standard AM 1.5G illumination (100 mW cm−2)) with a short-circuit current density (Jsc) of 14.4 mA cm−2, an open-circuit voltage (Voc) of 684 mV and a fill factor (ff) of 74.4%. In comparison, the device sensitized by the N719 dye shows an efficiency of 7.9%. The DSSC device sensitized by JH304 also exhibits excellent soaking stability under sunlight for 1000 h.

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 450–650nm. 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 400–750nm. All these new dyes are simple in structure, very easy to synthesize, and gives high Voc.

Indoline-based dyes with antenna groups for dye-sensitized solar cells

Indoline-based dyes (In-In and TPD-In dyes) with a homoleptic or a heteroleptic antenna group were designed, and their electronic and optical properties were investigated theoretically to enhance the photovoltaic performance in dye-sensitized solar cells (DSSCs). To gain insight into the factors responsible for photovoltaic efficiencies, we performed density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations for those dyes. The DFT and the TDDFT calculations showed that both the N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) antenna and the indoline electron donor in the TPD-In dye contributed to the transitions in the absorption spectrum, showing that the TPD-In dye had improved absorption property. We found that the effective use of an additional antenna group might take place for an appropriate design in which the highest occupied molecular orbital (HOMO) level for the antenna group is located higher than that for the electron donor. This study suggests that an indoline-based dye sensitizer would show improved photovoltaic performance in the conversion efficiency for DSSCs through the addition of a heteroleptic antenna group.

Carbazole Dyes with Ether Groups for Dye-Sensitized Solar Cells: Effect of Negative Charges in Dye Molecules on Electron Lifetime

In order to examine the effect of partial charges of dye molecules on charge recombination in dye-sensitized solar cells, we synthesized carbazole-based dyes with ether chains on a π-conjugated oligothiophene linker. The addition of negatively charged oxygen atoms on ether chains resulted in a decrease of electron lifetime, suggesting that partial charges on the dye increased I3- concentration at the surface of TiO2.

Carbazole Dyes with Ether Groups for Dye-Sensitized Solar Cells: Effect of Negative Charges in Dye Molecules on Electron Lifetime

Carbazole Dyes with Ether Groups for Dye-Sensitized Solar Cells: Effect of Negative Charges in Dye Molecules on Electron Lifetime

New Triphenylamine-Based Organic Dyes with Different Numbers of Anchoring Groups for Dye-Sensitized Solar Cells

We synthesized two organic dyes (TPA–CN1–R2 and TPA–CN2–R1) based on the TPA core unit having structure A–D–A, which contain the triphenylamine moiety as an electron donor and both cyanovinylene 4-nitrophenyl and carboxylic (anchoring) units as electron acceptors. Nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs) were fabricated using these dyes to investigate the effect of number of anchoring groups on their photovoltaic performance. The DSSCs based on TPA–CN1–R2 and TPA–CN2–R1 showed power conversion efficiency (PCE) of about 2.36% and 1.41%, respectively. The PCE has been significantly improved up to 4.37% and 2.8%, upon addition of 20 mM deoxycholic acid (DCA) to the dye solution for TiO2 sensitization. Coadsorption of DCA decreased dye coverage but significantly improved the value of the short-circuit photocurrent (Jsc). The breakup of π-stacked aggregates might improve the electron injection yield and thus Jsc. Electrochemical impedance spectra and current–voltage characteristics in the dark indicate that the electron lifetime was improved by coadsorption of DCA, accounting for the significant improvement of open-circuit voltage (Voc).

Photo-induced electron transfer study of D-π-A sensitizers with different type of anchoring groups for dye-sensitized solar cells

A new D-π-A organic dye HY102 with a lateral anchoring group and two reference dyes HY102-1 (using cyanoacrylic acid as an electron acceptor and the anchoring group) and HY102-2 (containing both cyanoacrylic acid and lateral carboxylic acid) have been synthesized. The optical and electrochemical test results from the three different styles of photosensitizers show that the excited electrons of the novel dye HY102 with lateral carboxylic acid group most probably are injected into the CB of TiO2 through the electron acceptor moiety close to the TiO2 surface by spatial transfer, not through the lateral anchoring group of the carboxylic acid. Research into the photo-induced electron transfer of the novel sensitizers with lateral anchoring system is reasonable and crucial for further improving efficiencies by modifying the molecular structures.