Groups For Dye-sensitized Solar Cells Research Articles

Theoretical study of tribranched organic sensitizer for Efficient Dye-sensitized solar cells

ABSTRACTWe investigated the effect of heteroleptic dual electron acceptor as a photosensitizer for the dye-sensitized solar cells (DSSCs). Novel tribranched organic dyes were designed with heteroleptic dual electron acceptors [cyanoacrylic acid (R1), and indolinum carboxyl acid (R2)] on each side of a triazine (TRZ) based organic dye and triphenylamine and the additional phenothiazine as an antenna group for DSSCs. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to estimate the photovoltaic properties of the dyes. The absorption spectrum of the dyes showed different forms because of the different energy levels of molecular orbital (MO) of each dye and intramolecular energy transfer. Considering overall properties, the asymmetric tribranched organic dye exhibited a high conversion efficiency performance for DSSCs. The findings of this work suggest that optimizing the branch of electron donors and acceptors in dye sensitizers based on asymmetric tribranched organic dye produces good photovoltaic properties for DSSCs.

Indeno[1,2-b]indole-based organic dyes with different acceptor groups for dye-sensitized solar cells

Four new metal-free organic dyes QX15–18 based on indeno[1,2-b]indole have been successfully designed and synthesized. These D–π–A type dyes consist of an indeno[1,2-b]indole donor and a benzene or thiophene π-bridge. In an attempt to tune their photoelectric properties, the effects of different acceptor groups including cyanoacrylic acid, rhodanine-3-acetic acid, and 2-(1,1-dicyanomethylene)rhodanine (DCRD) have been investigated. The dye QX15 with a cyanoacrylic acid acceptor exhibited a highest Voc of 813 mV and a high Jsc of 11.0 mA cm−2, generating a highest power conversion efficiency of 6.29%. Meanwhile, the dye QX18 with a DCRD acceptor and a thiophene π-bridge showed a significantly improved Jsc of 11.9 mA cm−2, which could be attributed to its red-shifted absorption spectra and high molar absorption coefficient.

A Push–Pull Porphyrin Dimer with Multiple Electron-donating Groups for Dye-sensitized Solar Cells: Excellent Light-harvesting in Near-infrared Region

A push–pull porphyrin dimer with multiple electron-donating groups has been synthesized as a sensitizer with an excellent light-harvesting ability in the near-infrared region for dye-sensitized solar cells (DSSCs). The DSSC based on the sensitizer exhibited the photocurrent generation exceeding a wavelength of 900 nm, together with a power conversion efficiency of 6.21% under AM 1.5 condition.

Benzoporphyrins bearing pyridine or pyridine-N-oxide anchoring groups as sensitizers for dye-sensitized solar cell

Novel benzoporphyrins bearing pyridine or pyridine-[Formula: see text]-oxide groups were prepared through a concise method based on a Pd0 catalyzed cascade reaction. These benzoporphyrins were examined as sensitizers for dye-sensitized solar cells. Vicinal pyridine and vicinal pyridine-[Formula: see text]-oxide groups were introduced as new types of anchoring/acceptor groups for dye-sensitized solar cells for the first time. While all the porphyrins showed solar to electricity conversion, benzoporphyrins bearing pyridine-[Formula: see text]-oxide anchoring groups displayed higher conversion efficiency than benzoporphyrins bearing pyridine-anchoring groups.Opp-dibenzoporphyrins display broadened and red-shifted UV-vis absorption and emission bands as compared with those of the monobenzoporphyrins, which arises from the fusion of one more benzene ring and the attachment of two more electron-withdrawing groups to the porphyrin [Formula: see text]-positions. Cyclic voltammetry (CV) data and DFT calculation data obtained for these porphyrins agree well with their UV-vis absorption and fluorescence spectroscopic data. The HOMO energy level derived from the first oxidation potentials indicate that regeneration of the resulting porphyrin radical cation by the redox mediator (I[Formula: see text]/I[Formula: see text] is thermodynamically feasible for all these benzoporphyrin sensitizers (3, 5, 8 and 10). On the other hand, excited state energy levels of these benzoporphyrins calculated from the CV data, the UV-vis and fluorescence spectroscopic data are all slightly lower than the energy level of the conduction band of TiO2, suggesting insufficient driving force for efficient electron injection from the porphyrin excited singlet state to the conduction band of TiO2.

New sensitizers containing amide moieties as electron-accepting and anchoring groups for dye-sensitized solar cells

Three sensitizers with amide moieties as electron-accepting and anchoring groups were synthesized for dye-sensitized solar cells, in which the pyrimidine-trione-based sensitizer showed an efficiency of 3.9%.

Synthesis and characterization of simple cost-effective trans-A2BC porphyrins with various donor groups for dye-sensitized solar cells

Zn(ii) porphyrin dyes have been synthesized in three steps and exhibited power conversion efficiencies of 2.1 to 4.2% which depend on the electron donating ability of the R group.

Julolidine--Based Organic Dyes with Neutral and Anion Anchoring Groups for Dye-Sensitized Solar Cells.

Two simple organic dyes (J1 and J2) containing julolidine as the electron donor were synthesized. The simple structure of julolidine attached to the cyanoacetic acid group formed two compounds (anion and neutral forms of E-CCVJ), which showed two different efficiencies when applied to dye-sensitized solar cells (DSSCs). Overall conversion efficiencies of 0.91% and 1.21% were obtained for DSSCs based on the cyanoacetic acid (J1) and cyanoacetate (J2) derived dyes, respectively. Compared to the cyanoacetic acid terminated dye, the current density, open circuit voltage and conversion efficiency of the solar cells based on cyanoacetate dye were increased by approximately 24%, 8% and 32%, respectively. The electrochemical impedance analysis showed that the better charge transfer of TiO2 (e-) and electron lifetime (τ(e)) for J2 dye as compared with J1. The power conversion efficiency was found to be quite sensitive to small structural changes to the anchoring moiety.

Synthesis and characterization of organic dyes bearing new electron-withdrawing group for dye-sensitized solar cells

Three new carbazole-based dyes (DB-CH, DTB-CH, DT-CH) have been synthesized. The dye structures were built from an aliphatic hexyl which served as an electron donor and barbituric acid, thiobarbituric acid and thiazolidine-2,4-dione moieties which served as acceptors. The photophysical and electrochemical properties of the dyes were investigated by UV spectroscopy and cyclic voltammetry (CV). The barbituric acid, thiobarbituric acid and thiazolidine-2,4-dione derivatives were found to affect both the molar extinction coefficients and λmax which was likely due to the extension of the π-conjugation structures of the dyes. In the best case, conversion efficiencies up to 2.16% under full sunlight irradiation were obtained for the DSSCs which incorporated these new dyes. Our study indicated that the inclusion of thiazolidine-2,4-dione as an electron acceptor in the dye structure can lead to an improvement in its photovoltaic performance.

Two New Dyes with Carboxypyridinium Regioisomers as Anchoring Groups for Dye-Sensitized Solar Cells

Two new organic dye-sensitized solar cell (DSSC) sensitizers bearing regioisomeric carboxyl-<i>N</i>-methylpyridinium moieties were prepared and fully characterized. Based on TD-DFT calculations, they were anticipated to show a significantly red-shifted absorption spectrum compared to normal carboxypyridines and other regioisomeric pyridinium salts. Although this prediction was met, the two regioisomers unexpectedly showed very different stabilities upon adsorption on TiO₂.

Porphyrin Sensitizers Bearing a Pyridine-Type Anchoring Group for Dye-Sensitized Solar Cells.

Three novel efficient donor-acceptor porphyrins, MH1-MH3, with a pyridine-type acceptor and anchoring group were synthesized and their optical, electrochemical, and photovoltaic properties investigated. Replacing the commonly used 4-carboxyphenyl anchoring group with 2-carboxypyridine, 2-pyridone, and pyridine did not significantly change the absorption and electrochemical properties of the porphyrin dyes. These new porphyrin dyes MH show power conversion efficiencies of 8.3%, 8.5%, and 8.2%, which are comparable to that of the benchmark YD2-o-C8 (η=8.25%) under similar conditions. It was demonstrated that 2-carboxypyridine is an efficient and stable anchoring group as MH1 and showed better cell performance and long-term stability than YD2-o-C8 under light soaking conditions.

Tropolone as a High-Performance Robust Anchoring Group for Dye-Sensitized Solar Cells.

A tropolone group has been employed for the first time as an anchoring group for dye-sensitized solar cells (DSSCs). The DSSC based on a porphyrin, YD2-o-C8T, with a tropolone moiety exhibited a power-conversion efficiency of 7.7 %, which is only slightly lower than that observed for a reference porphyrin, YD2-o-C8, with a conventional carboxylic group. More importantly, YD2-o-C8T was found to be superior to YD2-o-C8 with respect to DSSC durability and binding ability to TiO2 . These results unambiguously demonstrate that tropolone is a highly promising dye-anchoring group for DSSCs in terms of device durability as well as photovoltaic performance.

Tropolone as a High‐Performance Robust Anchoring Group for Dye‐Sensitized Solar Cells

AbstractA tropolone group has been employed for the first time as an anchoring group for dye‐sensitized solar cells (DSSCs). The DSSC based on a porphyrin, YD2‐o‐C8T, with a tropolone moiety exhibited a power‐conversion efficiency of 7.7 %, which is only slightly lower than that observed for a reference porphyrin, YD2‐o‐C8, with a conventional carboxylic group. More importantly, YD2‐o‐C8T was found to be superior to YD2‐o‐C8 with respect to DSSC durability and binding ability to TiO2. These results unambiguously demonstrate that tropolone is a highly promising dye‐anchoring group for DSSCs in terms of device durability as well as photovoltaic performance.

Molecular engineering of D-A-π-A dyes with 2-(1,1-dicyanomethylene)rhodanine as an electron-accepting and anchoring group for dye-sensitized solar cells

The electron-accepting and anchoring group plays a significant role on the optical and electrochemical properties of an organic dye. They also affect the intramolecular charge transfer, the electron injection processes and the adsorption mode, hence the photostability of the dye on TiO2 films. In this study, we have designed and synthesized two new D-A-π-A dyes (RD-III and RD-IV) with 2-(1,1-dicyanomethylene) rhodanine (DCRD) as electron-accepting and anchoring group. For comparison, an analogue of RD-III, namely CA-III, with cyanoacrylic acid (CA) as the acceptor was also prepared. We have carefully examined their optical and electrochemical properties, device performance and electrochemical impedance spectroscopy (EIS). Supplementary support is given by computational approach to gain in-depth insight into the adsorption states and electron contributions. The theoretical calculation of dye/(TiO2)38 displayed that the angle between the molecule of RD-III and the surface of TiO2 was only 31.840 in contrast to 97.160 for CA-III. This adsorption state can facilitate dye aggregation and charge recombination, resulting in a decrease of short circuit current density (Jsc) and open circuit voltage (Voc). Further improvement has been successfully made by adding long alkoxy chains with large steric hindrance. After introducing the alkoxy chains, the dihedral angle between RD-IV and TiO2 increased to 42.610 and the steric hindrance can inhibit dye aggregation and charge recombination. Therefore, higher photoelectric conversion efficiency of 5.53 % was obtained with RD-IV in DSSC devices compared with 4.51 % for DSSC based on RD-III.

Anchoring groups for dye-sensitized solar cells.

The dyes in dye-sensitized solar cells (DSSCs) require one or more chemical substituents that can act as an anchor, enabling their adsorption onto a metal oxide substrate. This adsorption provides a means for electron injection, which is the process that initiates the electrical circuit in a DSSC. Understanding the structure of various DSSC anchors and the search for new anchors are critical factors for the development of improved DSSCs. Traditionally, carboxylic acid and cyanoacrylic acid groups are employed as dye anchors in DSSCs. In recent years, novel anchor groups have emerged, which make a larger pool of materials available for DSSC dyes, and their associated physical and chemical characteristics offer interesting effects at the interface between dye and metal oxide. This review focuses especially on the structural aspects of these novel dye anchors for TiO2-based DSSCs, including pyridine, phosphonic acid, tetracyanate, perylene dicarboxylic acid anhydride, 2-hydroxylbenzonitrile, 8-hydroxylquinoline, pyridine-N-oxide, hydroxylpyridium, catechol, hydroxamate, sulfonic acid, acetylacetanate, boronic acid, nitro, tetrazole, rhodanine, and salicylic acid substituents. We anticipate that further exploration and understanding of these new types of anchoring groups for TiO2 substrates will not only contribute to the development of advanced DSSCs, but also of quantum dot-sensitized solar cells, water splitting systems, and other self-assembled monolayer-based technologies.

Synthesis, optical, electrochemical and photovoltaic properties of a D–π–A fluorescent dye with triazine ring as electron-withdrawing anchoring group for dye-sensitized solar cells

D–π–A fluorescent dye OUJ-1 with 1,3,5-triazine ring as electron-withdrawing anchoring group has been newly developed and its optical and electrochemical properties, and photovoltaic performance in a dye-sensitized solar cell were investigated.

Development of a functionally separated D–π-A fluorescent dye with a pyrazyl group as an electron-accepting group for dye-sensitized solar cells

A functionally separated D–π-A dye OUK-3 with a pyrazyl group as an electron-accepting group and a carboxyl group as an anchoring group has been newly developed as a photosensitizer for dye-sensitized solar cells.

Zinc phthalocyanine sensitizer having double carboxylic acid anchoring groups for dye-sensitized solar cells with cobalt(ii/iii)-based redox electrolyte

Double anchored ZnPc sensitizer PcS25 exhibited higher conversion efficiency in dye-sensitized solar cells with cobalt(ii/iii)-based redox electrolyte than single-anchored ZnPc sensitizers.

Theoretical Investigation on Novel Porphyrin Dyes with Functionalized Bridge and Donor Groups for Dye-Sensitized Solar Cells

A series of porphyrin dyes with functionalized bridge and donor groups are investigated as organic dyes in dyesensitized solar cells (DSSCs) using the density functional theory (DFT) and time-dependent DFT approach. Molecular geometries, electronic structures, optical absorption spectra, and light-harvesting efficiency are analyzed in tetrahydrofuran solution. Our results show that bithiophenyl, biphenyl, and naphthyl groups on bridge decrease the HOMO–LUMO gaps and lead to obvious red shift of spectra with stronger intensities at the long wavelength region. Dithiafulvenyl, carbazolyl and naphthyl groups on donor subunit result in similar HOMO– LUMO gaps to the dye YD2-o-C8, but promote the absorption intensity significantly. The designed porphyrin dyes show better light-harvesting efficiency and coverage range along with the structural optimizations on bridge and donor groups. This theoretical investigation would facilitate the screening of the functionalized bridge and donor groups for efficient porphyrin dyes in DSSCs.

A Zinc Porphyrin Sensitizer Modified with Donor and Acceptor Groups for Dye-Sensitized Solar Cells

E-mail: hong5506@incheon.ac.krReceived March 17, 2014, Accepted July 9, 2014In this article, we have designed and synthesized a novel donor-π-acceptor (D-π-A) type porphyrin-basedsensitizer (denoted UI-5), in which a carboxyl anchoring group and a 9,9-dimethyl fluorene were introduced atthe meso-positions of porphyrin ring via phenylethynyl and ethynyl bridging units, respectively. Long alkoxychains in ortho-positions of the phenyls were supposed to reduce the degree of dye aggregation, which tendsto affect electron injection yield in a photovoltaic cell. The cyclic voltammetry was employed to determine theband gap of UI-5 to be 1.41 eV based on the HOMO and LUMO energy levels, which were estimated by theonset oxidation and reduction potentials. The incident monochromatic photon-to-current conversion efficiencyof the UI-5 DSSC assembled with double-layer (20 nm-sized TiO

Novel ruthenium sensitizers having different numbers of carboxyl groups for dye-sensitized solar cells: effects of the adsorption manner at the TiO₂ surface on the solar cell performance.

Two novel ruthenium sensitizers having multiple carboxyl groups ((TBA)[Ru{4'-(3,4-dicarboxyphenyl)-4,4″-dicarboxyterpyridine}(NCS)3] (TUS-21) and (TBA)[Ru{4'-(3-carboxyphenyl)-4,4″-dicarboxyterpyridine}(NCS)3] (TUS-37); TBA = tetrabutylammonium) have been synthesized as improved model sensitizers for the previously reported ruthenium sensitizer TUS-20 ((TBA)[Ru{4'-(3,4-dicarboxyphenyl)terpyridine}(NCS)3]). The absorption maxima of two MLCT bands and the absorption onsets of TUS-21 and TUS-37 were shifted to longer wavelengths of about 30 nm in comparison to those of TUS-20 by introducing a carboxyl group to the each terminal pyridine ring of the terpyridine ligand. TUS-21 and TUS-37 showed quite similar adsorption behaviors to the TiO2 surface, and this adsorption behavior was found to be different from that of TUS-20. ATR-IR measurements revealed that TUS-21 and TUS-37 bind to the TiO2 surface by using two carboxyl groups at the 3-position of the phenyl ring and at one of the terminal pyridine rings of the terpyridine ligand, while TUS-20 is reported to bind by using two carboxyl groups at the 3,4-dicarboxyphenyl unit. The dye-sensitized solar cell (DSC) with TUS-21 exhibited 10.2% conversion efficiency, which is much higher than that of the DSC with TUS-20 (7.5%), under AM 1.5 (100 mW/cm(2)) irradiation.