Enhancement in the photostability of natural dyes for dye‐sensitized solar cell (DSSC) applications: a review

The advancements in the generation of solar cells have created a landmark to design a cost‐effective, less weight, biocompatible, and environmental‐friendly solar cell. Dye‐sensitized solar cells (DSSCs) have become a topic of significant research in the recent years because of their imperative role in the zone of harvesting energy from the renewable source, and it appears to be a promising candidate for the triumph because of its low cost and ease of preparation. The use of synthetic dyes as a sensitizer for DSSC provides better efficiency and high durability. Unfortunately, they suffer from several margins such as higher cost and usage of toxic materials. These downsides have opened up for alternative sensitizer such as biocompatible natural dyes. Natural dyes contain plant pigments such as carotenoid, flavonoid, betalains, and chlorophyll that act as sensitizers (dye) for DSSC. But, the efficiency of natural dyes is not up to the mark mainly due to photoinstability of natural dye in the presence of sunlight that leads to photodegradation. The stability issues are mainly due to interaction of natural dyes with photoelectrode. The photoelectrodes in DSSC are semiconductor materials with superior characteristic of photocatalytic activity (PCA). The PCA of titanium dioxide (TiO₂) generates high energetic free electrons on the surface of film that produce free radical ions in contact with moisture. These free radical ions readily degrade the organic matter present nearby (natural dye in DSSC). Thus, the PCA of photoelectrode is responsible for the photodegradation of dyes causing photoinstability. The main objective of this review is to study the photoinstability of natural dyes in DSSC. In this regard, the DSSC is concentrated into sections, and the stability issues due to PCA of photoelectrode are studied individually in the view of considering the DSSC operating with iodide‐based electrolytes and platinum as counter electrode only. Various algae groups are featured as a study tool to overview the dye interaction with photoelectrode. It highlights the application of Z‐scheme of photosynthesis to DSSC to have a broader perception on the working of DSSC and also shows some of the ways for improving the stability of dyes by suppressing or reducing the PCA of photoelectrode. Copyright © 2017 John Wiley & Sons, Ltd.     

Novel dye based photoelectrode for improvement of solar cell conversion efficiency

We have explored the application of natural dyes extracted from beetroot in Dye sensitized solar cell (DSSC). The main pigment is betacyanin which was obtained by separation and purification from the extract. The photo electrochemical performance of the DSSC based on these dyes showed that the photo voltage and photocurrent 435 mV, 9.86 mA, respectively. The overall conversion efficiency of nano WO₃ coated TiO₂ dye-sensitized solar cells exhibits a higher conversion efficiency of 2.2%. The photo electrochemical performance of beetroot extract demonstrate that betacyanin dye was the most effectual component of the sensitizer for DSSC because of the simple preparation technique, widely available and low cheap cost.     

Characteristics of triphenylamine-based dyes with multiple acceptors in application of dye-sensitized solar cells

We report the synthesis and photophysical/electrochemical properties of triphenylamine (TPA)-based multiple electron acceptor dyes (TPAR1, TPAR2, and TPAR3) as well as their applications in dye-sensitized solar cells (DSSCs). In these dyes, the TPA group and the rhodanine-3-acetic acid play the role of the basic electron donor unit and the electron acceptor, respectively. It was found that introduction of two rhodanine-3-acetic acid groups into the TPA unit (TPAR2) exhibited better photovoltaic performance due to the increase with a red shift and broadening of the absorption spectrum. The monolayer of these TPA-based dyes was adsorbed on the surface of nanocrystalline TiO₂ mesoporous electrode with the thickness of ∼6 μm, polyethylene oxide (PEO) used as the matrix of gel electrolyte, and 4-nm thick Pt used as a counter-electrode. Photovoltaic device can be realized in a single quasi-solid-state DSSC. TPAR2-based gel DSSC had an open circuit voltage and short circuit current density of about 541 and 10.7 mA cm⁻², respectively, at 1-sun.     

Effect of using betalain,anthocyanin and chlorophyll dyes together as a sensitizer on enhancing the efficiency of dye-sensitized solar cell

The paper explored the mechanism of working of dye sensitizers for the improvement of efficiency of environmentally benign dye-sensitized solar cells (DSSC). The identified natural dyes namely anthocyanin (A), betalain (B) and chlorophyll (C) were extracted from Roselle (Hibiscus sabdariffa L.), spinach (Spinacia oleracea) and beetroot (Beta vulgaris) respectively. Light absorption performance of dyes was recorded by ultraviolet-visible (UV-vis) spectroscopic analysis followed by direct and indirect band gap calculation. The effect of functional groups present in the dyes studied by Fourier transform infrared spectroscopy (FTIR) and binding of the dyes on TiO₂ through surface morphology of sheets was identified employing field emission scanning electron microscopy (FESEM). Photovoltage characteristics (I-V) and induced photon to current efficiency (IPCE) measurements were also noted followed by the stability studies. The N3 (synthetic dye chosen for the reference) dye-based cell showed the highest efficiency of 6.19% out of all of 11 cells fabricated using different sensitizers. The DSSC fabricated using the novel mixed dye (ABC) mixture gave the highest efficiency of 3.73%, however it showed similar drop (almost 22%) in efficiency as that with of N3 dye in stability studies. The mechanism for the increase in the overall power conversion efficiency of DSSC was also suggested.     

Fluorene based organic dyes for dye sensitised solar cells: structure–property relationships

Abstract

Dye sensitised solar cells (DSSCs) have received immense attention in recent years as they offer the possibility of low cost conversion technology of light energy to electrical energy. Organic dyes have been demonstrated as sensitisers in DSSCs with promising photoelectrical conversion efficiencies. Though several polyaromatic hydrocarbon based organic dyes have been developed for use in DSSC, dipolar compounds featuring a fluorene unit have shown promising potential as light harvesting component. In this review, we present a comprehensive survey of the organic dyes containing fluorene either in the donor part or as a π linker in the conjugation pathway in a conventional donor–π–acceptor molecular configuration. Structural features of the molecular materials were correlated with the functional properties, such as optical absorption and oxidation potential.     

Mordant dyes as sensitisers in dye-sensitised solar cells

Many mordant dyes commonly used in the textile industry form coordination complexes at the surface of nanocrystalline TiO₂. Dyes having a salicylate chelating group are particularly effective. Forty-nine commercial mordant dyes were studied as sensitisers in a non-optimised dye-sensitised solar cell (DSSC) and their performance compared to the N3 ruthenium complex. Although N3 produced the highest output, six mordant dyes produced photocurrents >0.2 mA. UV–visible spectra of the dye-complexed photoanodes suggest that some mordant dyes are more strongly bound to the TiO₂ surface than N3. Photocatalytic oxidation of these dyes does not appear to occur in a DSSC environment.     

St. Lucie cherry,yellow jasmine,and madder berries as novel natural sensitizers for dye‐sensitized solar cells

Natural dyes extracted from fruits, vegetables, flowers, and leaves are considered as promising alternative sensitizers to replace synthetic dyes for dye‐sensitized solar cells (DSSCs). Generally, solar activity of natural dyes stem from anthocyanin pigment. Carbonyl, carboxyl, and hydroxyl groups present in the anthocyanin molecule improve the adsorption ability of dye on TiO₂ and therefore facilitate charge transfer. Here, for the first time, novel natural dyes extracted from St. Lucie cherry, yellow jasmine, and madder berries are reported to act as sensitizer in DSSCs. These novel natural dye extracts are prepared by dissolving related fruits in ethanol. The ingredient of the dyes is identified by FT‐IR spectroscopy. Accordingly, FT‐IR spectrum reveals that novel natural dye extracts exhibit all the characteristic peaks of anthocyanin pigment. Specifically, St. Lucie cherry consists of more distinct carbonyl group than other sources. Also, photoanodes composed of three TiO₂ layers are prepared by using a spin‐coating method. Then, they are immersed into natural dyes and analyzed by conducting UV‐Vis spectroscopy. Compared with bare TiO₂, natural dye–loaded photoanodes demonstrate far higher absorption ability in the visible region. After fabrication of devices with different novel natural dye sensitizers, current‐voltage characteristics and electrochemical impedance spectroscopy measurements are performed. The best power conversion efficiency (PCE) of 0.19% is obtained by sensitization of St. Lucie cherry with an open‐circuit voltage (V_oc) of 0.56 V, short‐circuit current density (J_sc) of 181 μA cm^?2, and fill factor (FF) of 0.55. Furthermore, St. Lucie cherry–sensitized devices show the lowest charge transfer and highest recombination resistances. This result can be attributed to the obvious carbonyl group exhibited by St. Lucie cherry.     

Synthesis of TiO2 nanoparticles at low hydrothermal temperature and its performance for DSSC sensitized using natural dye extracted from Melastoma malabathricum L. seeds

Efficiency of a dye‐sensitized solar cell (DSSC) device depends on its semiconductor layer and the sensitizing dye to absorb the light. This work seeks to obtain the best solvent for the natural dye extraction from Melastoma malabathricum L. seeds. The extracted dye is used as sensitizer on TiO₂ nanoparticles produced via hydrothermal but optimized at relatively low temperature. Infrared characterization of the extracted dyes showed differences in functional groups using different solvents, whereas ultraviolet visible examination of the dyes showed differences in intensity along the spectrum ranges of 600 to 400 nm with maximum absorption around 550 to 500 nm. Thermal analysis revealed that the natural dye should be stable around room temperature. Analysis on the synthesized TiO₂ nanoparticles showed that the average crystallite size reported in the previous work is consistent with crystallite sizes observed in the transmission electron microscope images. Photoactivity examination showed that the DSSC sensitized using natural dye extracted with ethanol containing 20% distilled water on TiO₂ synthesized at 150°C has an efficiency of 5.7%, whereas the one on commercial TiO₂ P25 Degussa has an efficiency of 3.0%. The DSSC device sensitized using commercial dye on TiO₂ synthesized at 150°C has an efficiency of 4.4%, whereas the one on TiO₂ P25 Degussa has an efficiency of 4.0%. This result is promising for further development of the DSSC device using TiO₂ nanoparticles synthesized at low hydrothermal temperature and sensitized with the natural dye.     

Synthesis of new low band gap dyes with BF2-azopyrrole complex and their use for dye-sensitized solar cells

The diazonium salt derived from 4-aminobenzoic acid, 4-aminophenol or 2-aminophenol reacted with half equivalent of pyrrole to afford symmetrical 2,5-bisazopyrroles. They reacted subsequently with boron trifluoride in the presence of triethylamine to afford the corresponding BF₂-azopyrrole complexes D1, D2 and D3 respectively. They were soluble and stable in nonprotic solvents such as chloroform, dichloromethane and tetrahydrofuran but unstable in protic solvents such as ethanol. Their absorption spectra were broad with optical band gap of 1.49-1.70 eV. Among these dyes D2 displayed the broader absorption spectrum with low band gap of 1.49 eV. We have utilized these complexes as photosensitizers for quasi solid state dye-sensitized solar cells (DSSCs) and achieved power conversion efficiency in the range of 4.0-6.0%. We have also found that the co-adsorption of citric acid hindered the formation of dye aggregates and might improve the electron injection efficiency leading to an enhancement in short circuit photocurrent. This work suggests that metal-free dyes based on BF₂-azopyrrole complex are promising candidates for improvement of the DSSC performance.     

Status and outlook of sensitizers/dyes used in dye sensitized solar cells (DSSC): a review

Dye‐sensitized solar cells (DSSCs) have become a topic of significant research in the last two decades because of their scientific importance in the area of energy conversion. Currently, DSSC is using inorganic ruthenium (Ru)‐based, metal‐free organic dyes, quantum‐dot sensitizer, perovskite‐based sensitizer, and natural dyes as sensitizer. The use of metal‐free, quantum‐dot sensitizer, perovskite‐based sensitizer, and natural dyes has become a viable alternative to expensive and rare Ru‐based dyes because of low cost, ease of preparation, easy attainability, and environmental friendliness. Most of the alternatives to Ru‐based dyes have so far proved inferior to the Ru‐based dyes because of their narrow absorption bands (Δλ ≈ 100–250 nm), adverse dye aggregation, and instability. This review highlights the recent research on sensitizers for DSSC, including ruthenium complexes, metal‐free organic dyes, quantum‐dot sensitizer, perovskite‐based sensitizer, mordant dyes, and natural dyes. It also details and tabulates all types of sensitizer with their corresponding efficiencies. Plot of progress in efficiency (η) of DSSC till date based on different types of sensitizers is also presented. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.     

Algal buffer layers for enhancing the efficiency of anthocyanins extracted from rose petals for natural dye‐sensitized solar cell (DSSC)

Natural dye‐sensitized solar cells (DSSCs) are becoming promising candidates for replacing synthetic dyes. Anthocyanins, a flavonoid pigment which is responsible for the coloration in fruits and flowers, have shown productive results in employing them as natural dye for DSSC. But unfortunately, they exhibit low efficiency compared with synthetic dyes. Probing the reasons for the low efficiency of anthocyanin paves way for finding solution to increase the efficiency. This paper lists the important factors that are responsible for anthocyanin instability in DSSC. As a remedial measure, this paper introduces two buffer layer made of algal byproducts—sodium alginate and Spirulina. Rutile phase TiO₂ nanorods prepared by hydrothermal method were used as photoelectrode and are subsequently characterized by X ray diffraction, transmission electron microscopy, and optical studies. The use of sodium alginate above the photoelectrode has proved to improve the dye concentration in the film by introducing more hydroxyl groups on the surface of TiO₂. Anthocyanins extracted from rose petals using citric acid as solvent were used as dye for DSSC. Prior to the sensitization process with anthocyanin dye, the TiO₂ film (with sodium alginate) was sensitized with Spirulina. The chlorophylls, xanthophylls, phycocyanins, and amino acids present in Spirulina assist the anthocyanins to bond with TiO₂ efficiently. This helps in enhancing the efficiency of anthocyanins of rose dye from 0.99% to 1.47%.     

Improved performance of a dye-sensitized solar cell using a TiO2/ZnO/Eosin Y electrode

TiO₂/ZnO/Eosin Y structure films were prepared by a one-step cathodic electrodeposition method and used as a photoanode in a dye-sensitized solar cell (DSSC). Using this TiO₂/ZnO/Eosin Y electrode in DSSC, the degradation of the cell with time was reduced and I_SC, V_OC and fill factor values were increased. The use of a thin ZnO layer, permitted the formation of an energy barrier at the electrode/electrolyte interface, thus reducing recombination rate and improving cell performance. In addition, the adsorbed dye molecules prepared by one-step cathodic electrodeposition with ZnO were very stable compared with that prepared by conventional immersing method, as evidenced by UV/vis absorption spectroscopy measurements.     

Dye-sensitized solar cell using natural dyes extracted from rosella and blue pea flowers

Dye-sensitized solar cells (DSSCs) were fabricated using natural dyes extracted from rosella, blue pea and a mixture of the extracts. The light absorption spectrum of the mixed extract contained peaks corresponding to the contributions from both rosella and blue pea extracts. However, the mixed extract adsorbed on TiO₂ does not show synergistic light absorption and photosensitization compared to the individual extracts. Instead, the cell sensitized by the rosella extract alone showed the best sensitization, which was in agreement with the broadest spectrum of the extract adsorbed on TiO₂ film. In case that the dyes were extracted at , using water as extracting solvent, the energy conversion efficiency (η) of the cells consisting of rosella extract alone, blue pea extract alone and mixed extract was 0.37%, 0.05% and 0.15%, respectively. The sensitization performance related to interaction between the dye and TiO₂ surface is discussed. The explanations are supported by the light absorption of the extract solution compared to extracts adsorbed on TiO₂ and also dye structures. The effects of changing extracting temperature, extracting solvent and pH of the extract solution are also reported. The efficiency of rosella extract sensitized DSSC was improved from 0.37% to 0.70% when the aqueous dye was extracted at instead of and pH of the dye was adjusted from 3.2 to 1.0. Moreover, DSSC stability was also improved by the changes in conditions. However, the efficiency of a DSSC using ethanol as extracting solvent was found to be diminished after being exposed to the simulated sunlight for a short period.     

Low band gap dyes based on 2-styryl-5-phenylazo-pyrrole: Synthesis and application for efficient dye-sensitized solar cells

A new series of low band gap dyes, C1, C2 and S, based on 2-styryl-5-phenylazo-pyrrole was synthesized. These dyes contain one carboxy, two carboxy and one sulfonic acid anchoring groups, respectively. They were soluble in common organic solvents, showed long-wavelength absorption maximum at ∼620 nm and optical band gap of 1.66-1.68 eV. The photophysical and electrochemical properties of these dyes were investigated and found to be suitable as photosensitizers for dye sensitized solar cells (DSSCs). The quasi solid state DSSCs with dye S showed a maximum monochromatic incident photon to current efficiency (IPCE) of 78% and an overall power conversion efficiency (PCE) of 4.17% under illumination intensity of 100 mW cm⁻² (1.5 AM), which is higher than the other dyes (3.26% for C2 and 2.59% for C1). Even though dye S contains one sulfonic acid anchoring group, the higher PCE for the DSSCs based on this dye has been attributed to the higher dye loading at the TiO₂ surface and enhanced electron lifetime in the device, as indicated by absorption spectra and electrochemical impedance spectra measurements. Finally, by increasing the molecular weight of poly(ethylene oxide) (PEO) in electrolyte, the PCE also increases up to 4.8% for the electrolyte with PEO molecular weight of 2.0 × 10⁶. This improvement has been attributed to the enhancement in iodide ions diffusion due to the increase in free volume of polymer gel electrolyte.     

Carbazole based D-A-π-A chromophores for dye sensitized solar cells: Effect of the side alkyl chain length on device performance

A series of Carbazole based Donor-Acceptor-π Bridge-Acceptor (D-A-π-A) dyes that contain different alkyl side chains with different lengths have been synthesized. Electrochemical and optical properties of these dyes were demonstrated by impedance spectroscopy, cyclic voltammetry, UV–Vis absorption and fluorescence spectroscopy, respectively. Herein, we report PV performance of dye-sensitized solar cells depending on the molecular structure of the dyes in terms of comparison of alkyl chain length on the carbazole moiety using an ionic liquid based electrolyte under standard AM 1.5 illumination. The results demonstrate that the dye containing alkyl chain with 4C atoms exhibited better performance compared to alkyl chains with 2C, 6C and 12C atoms.     

Synergistic enhancements in the performances of dye-sensitized solar cells by the scattering and plasmon resonance of Au-nanoparticle multi-shell hollow nanospheres

Novel multi-shell hollow SiO₂@Au@TiO₂ (HSAT) nanospheres are synthesized by multi-step method. Composite photoanodes and Dye-sensitized solar cells (DSSCs) with different amount of HSAT nanospheres are studied. The study indicates that the HSAT nanospheres have enhanced the scattering and absorption of incident light in the photoanode, reduced the interface transmission resistance, increased the electron lifetime, and thus significantly improved performance of DSSCs. The maximal J_sc and photoelectric conversion efficiency (PCE) obtained in the optimal DSSC doped with HSAT of 3.0% are 15.83 mA cm⁻² and 7.21%, greatly enhanced by 21.0% and 20.4%, respectively, compared with those of the pure TiO₂-based DSSC. These remarkable enhancements in DSSCs performance can be attributed to the synergistic and complementary effects of the localized surface plasmon resonance and strong light scattering of HSAT nanospheres, which has significantly improved the absorption and utilization on incident light and thus the PCE of the DSSCs. Such synergistic and complementary effects of the different functions are also likely expected to play roles in the performance improvements in other solar cells.     

Highly efficient solid-state dye-sensitized TiO2 solar cells via control of retardation of recombination using novel donor-antenna dyes

Two series of heteroleptic tris(bipyridyl)Ru(II) and bis(bipyridyl)(NCS)₂Ru(II) complexes have been synthesized and characterized. This is a part of a new concept of covalent linkage of donor-antenna groups, e.g., triphenylamine or N,N′-bis(phenyl)-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) to Ru(II) dye center. For the covalent attachment of donor units, a multi-step synthesis was carried out starting from 4,4′-dimethyl-2,2′-bipyridine followed by chlorination and Wittig reaction with donor aldehydes. This was followed either by a metallation reaction using bis(4,4′-dicarboxy-2,2′-bipyridyl)Ru(II)dichloride ((bpy(COOH)₂Ru(II)2Cl₂ 2H₂O) as precursor to get tris(bipyridyl) dyes or by a one pot synthesis starting from dichloro(p-cymene)Ru(II) dimer resulting in bis(bipyridyl)(NCS)₂ dyes. The complexes (bpy(COOH)₂)₂(bpyMe₂)Ru(II) 2PF₆ and (bpy(COOH)₂)(bpyMe₂)(NCS)₂Ru(II) without donor-antenna groups were also prepared to study and compare the properties. The influence of donor-antenna groups in these complexes was studied using UV–Vis spectroscopy and cyclic voltammetry. The heteroleptic complexes carrying donor groups show appreciably broad absorption ranges and extraordinarily high extinction coefficients. These high extinction coefficients are explained as due to the extended delocalization of π-electrons in the donor-antenna ligands. The HOMO/LUMO energy values obtained from cyclic voltammetry support the multi-step charge transfer cascade possible in these donor-antenna dyes. Examples of solid-state dye-sensitized solar cell utilizing these novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies of up to 3.4%, for the dye carrying a TPD donor group as measured under AM 1.5 spectral conditions. This is attributed to highly efficient light harvesting of these novel dyes and the improved charge transfer dynamics at TiO₂–dye and dye–hole conductor interfaces.     

Influence of electrolyte on the photovoltaic performance of a dye-sensitized TiO2 solar cell based on a Ru(II) terpyridyl complex photosensitizer

We have investigated the influence of electrolyte composition on the photovoltaic performance of a dye-sensitized nanocrystalline TiO₂ solar cell (DSSC) based on a Ru(II) terpyridyl complex photosensitizer (the black dye). We have also spectroscopically investigated the interaction between the electrolyte components and the adsorbed dye. The absorption peaks attributed to the metal-to-ligand charge transfer transitions of the black dye in solution and adsorbed on a TiO₂ film, were red-shifted in the presence of Li cations, which led to an expansion of the spectral response of the solar cell toward the near-IR region. The photovoltaic performance of the DSSC based on the black dye depended remarkably on the electrolyte composition. We developed a novel efficient organic liquid electrolyte containing an imidazolium iodide such as 1,2-dimethyl-3-n-propylimidazolium iodide or 1-ethyl-3-methylimidazolium iodide (EMImI) for a DSSC based on the black dye. A high solar energy-to-electricity conversion efficiency of 9.2% (J_sc=19.0 mA cm⁻², V_oc=0.67 V, and FF=0.72) was attained under AM 1.5 irradiation (100 mW cm⁻²) using a novel electrolyte consisting of 1.5 M EMImI, 0.05 M iodine, and acetonitrile as a solvent with an antireflection film.     

Evaluation on over photocurrents measured from unmasked dye-sensitized solar cells

We have investigated the change in photocurrent density (J_SC) of dye-sensitized solar cell (DSSC) before and after covering an aperture mask on the cell, especially its dependence on solar absorption range in dye. Four different dyes having absorption threshold at 460 nm (P5), 520 nm (TA-St-CA), 680 nm (N719) and 820 nm (N749) are tested. J_SC of the DSSC without mask decreases after mask, where the decreasing rate (△J_SC = J_SC (no mask) − J_SC (with mask)/J_SC (no mask)) becomes larger when dye absorption threshold decreases. △J_SC at the given TiO₂ film thickness of 10 μm is determined to be about 20%, 15% and 13% for P5, TA-St-CA and N719-N749, respectively, which is reduced to 14% (TA-St-CA), 11.3% (N719) and 10.5% (N749) after increasing the thickness to 20 μm, except for P5 dye remaining unchanged. According to the analysis based on IPCE and photon flux data, the over photocurrents observed for the unmasked dye-sensitized solar cells and their dependence on dye absorption range are found to be attributed to diffuse light leaving the dye-adsorbed TiO₂ active area.     

Dye-sensitized nanocrystalline TiO2 solar cells based on novel coumarin dyes

We have developed dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs) based on novel coumarin-dye photosensitizers. The absorption spectra of these novel dyes are red-shifted remarkably in the visible region relative to the spectrum of C343, a conventional coumarin dye. Introduction of a methine unit (–CH=CH–) connecting the cyano (–CN) and carboxyl (–COOH) groups into the coumarin framework expanded the π-conjugation in the dye and thus resulted in a wide absorption in the visible region. These novel dyes performed as efficient photosensitizers for DSSCs. A DSSC based on 2-cyano-5-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)-penta-2,4-dienoic acid (NKX-2311), produced a 6.0% solar energy-to-electricity conversion efficiency (η), the highest performance among DSSCs based on organic-dye photosensitizers, under AM 1.5 irradiation (100 mW cm^–2) with a short-circuit current density (J_sc) of 14.0 mA cm^–2, an open-circuit voltage (V_oc) of 0.60 V, and a fill factor of 0.71. Our results suggests that the structure of NKX-2311 whose carboxyl group is directly connected to the –CH=CH– unit, is advantageous for effective electron injection from the dye into the conduction band of TiO₂. In addition, the cyano group, owing to its strong electron-withdrawing ability, might play an important role in electron injection in addition to a red shift in the absorption region. On a long-term stability test under continuous irradiation with white light (80 mW cm^–2), stable performance was attained with a solar cell based on the NKX-2311 dye with a turnover number of 2.6×10⁷ per one molecule.