Synthetic Strategy of Low-Bandgap Organic Sensitizers and Their Photoelectron Injection Characteristics

Kim, Sukwon; Lim, Hyeoncheol; Kim, Kwang-Hyun; Kim, Chulhee; Kang, Taejoon; Ko, Min Jae; Kim, Kyungkon; Park, Nam‐Gyu

doi:10.1109/jstqe.2010.2042683

Cited by 16 publications

(5 citation statements)

References 44 publications

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“…Park et al reported BTD-based sensitizers 11 and 12. 33 In 11, the anchoring group of cyanoacrylic acid is directly connected to the BTD core, while in 12, the BTD and cyanoacrylic acid are separated by a phenylenevinylene, which increases the distance and conjugation between BTD and the anchoring group. Intriguingly, the p-extension by phenylenevinylene does not lead to any red-shift of the CT band (498 and 494 nm for 11 and 12, respectively).…”

Section: Benzothiadiazole (Btd) Based D-a-p-a Featured Organic Sensit...mentioning

confidence: 99%

Organic sensitizers from D–π–A to D–A–π–A: effect of the internal electron-withdrawing units on molecular absorption, energy levels and photovoltaic performances

2013

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The high performance and low cost of dye-sensitized solar cells (DSSCs) have drawn great interest from both academic and industrial circles. The research on exploring novel efficient sensitizers, especially on inexpensive metal-free pure organic dyes, has never been suspended. The donor-π bridge-acceptor (D-π-A) configuration is mainstream in the design of organic sensitizers due to its convenient modulation of the intramolecular charge-transfer nature. Recently, it has been found that incorporation of additional electron-withdrawing units (such as benzothiadiazole, benzotriazole, quinoxaline, phthalimide, diketopyrrolopyrrole, thienopyrazine, thiazole, triazine, cyanovinyl, cyano- and fluoro-substituted phenyl) into the π bridge as internal acceptors, termed the D-A-π-A configuration, displays several advantages such as tuning of the molecular energy levels, red-shift of the charge-transfer absorption band, and distinct improvement of photovoltaic performance and stability. We apply the D-A-π-A concept broadly to the organic sensitizers containing additional electron-withdrawing units between electron donors and acceptors. This review is projected to summarize the category of pure organic sensitizers on the basis of the D-A-π-A feature. By comparing the structure-property relationship of typical photovoltaic D-A-π-A dyes, the important guidelines in the design of such materials are highlighted.

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Section: Benzothiadiazole (Btd) Based D-a-p-a Featured Organic Sensit...mentioning

confidence: 99%

Organic sensitizers from D–π–A to D–A–π–A: effect of the internal electron-withdrawing units on molecular absorption, energy levels and photovoltaic performances

2013

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“…These molecules displayed better photovoltaic performance by broadening the absorption spectra, extending the light‐absorption range. A variety of auxiliary A groups were reported previously, such as benzothiadiazole, benzotriazole, diketopyrrolopyrrole, fluoro‐substitution, isoindigo, quinoxaline, thioazole, and triazine to tailor the absorption energy levels. In our earlier report, we have shown that by the introduction of quinoxaline and quinoxalinoid functionalities, the absorption extinction coefficient may be doubled .…”

Section: Introductionmentioning

confidence: 97%

High‐Performance Organic Dyes with Electron‐Deficient Quinoxalinoid Heterocycles for Dye‐Sensitized Solar Cells under One Sun and Indoor Light

et al. 2019

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A series of Y‐shaped sensitizers incorporating quinoxaline or quinoxalinoid moieties were prepared and applied in dye‐sensitized solar cells (DSSCs). By the introduction of quinoxalinoid functionalities, the absorption extinction coefficients could be enhanced. The molecular structures were modified by introducing an extra acceptor group (A) between a donor (D) and a π‐bridge (D–A–π–A) and also by incorporating electron‐donating substituents at various positions of the quinoxalinoid moiety. Some of the dyes and mixtures thereof were found to exhibit good light‐harvesting efficiencies under both sunlight and indoor light, with efficiencies up to 7.92 % under one sun (AM 1.5G). When operated under indoor light, the efficiency could be boosted to 27.76, 28.74, and 30.45 % under 600, 1000, 2500 lux illumination, respectively. The best performance could be ascribed partly to an improved dye coverage on the TiO2 surface.

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“…This allows for fine-tuning the spectral and electronic features as well as for a control over charge-transfer kinetics and electronic coupling to TiO 2 . Understanding the influence of structural variations to the sensitizer, such as the length of π-conjugation or anchoring/acceptor group choice on the DSSC device performance, is crucial for advancing this field and technology. , Critical factors that influenced performance properties are (i) the excited-state redox potentials, which should be properly aligned with the conduction band of TiO 2 , (ii) the light-harvesting features of the sensitizer, (iii) the conjugation across the donor and anchoring groups, and (iv) the electronic coupling between the lowest unoccupied molecular orbital (LUMO) and the conduction band of the TiO 2 . It has been shown that a sensitive interplay between all of these factors governs a vectorial and efficient electron flow from the electron donating moiety of the dye toward the semiconductor surface.…”

Section: Introductionmentioning

confidence: 99%

Position-Dependent Extension of π-Conjugation in D-π-A Dye Sensitizers and the Impact on the Charge-Transfer Properties

Wielopolski

Kim²,

Jung³

et al. 2013

J. Phys. Chem. C

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A series of five organic donor-π-bridge-acceptor (D-π-A) sensitizers is investigated within the context of their photoinduced charge-transfer properties. Thereby, the focus is set on the impact of structural modifications of the molecular architecture on the π-systems of the dyes. In particular, two different modes of systematic extension of the sensitizers' π-systems, namely, (i) within the electron donating site and (ii) within the π-bridge, are investigated by means of steady-state and time-resolved spectroscopic methods. The photophysical studies of the molecules in solution and as deposited on Al 2 O 3 or TiO 2 films reveal that different effects on the charge-transfer characteristics evolve dependent where − within the molecular structure − the modification of the π-system is performed. Hence, π-extension of the donor sites, for instance, leads to a strong red shift of the absorption features and a variation of light-harvesting properties. Modifying the π-bridges results in a spatial decoupling of the HOMO and LUMO orbitals, which goes along with changes of the electronic coupling to TiO 2 . Furthermore, solution studies show that the electronic structure of the dyes governs their singlet excited-state features. As shown, the results obtained from these studies then allow important predictions about the deactivation of the excited states of these molecules adsorbed on TiO 2 . Finally, quantum chemical methods − among others, time-dependent density functional theory calculations − provide conclusive insight into the relationship between the electronic structure of the dyes and its impact on the photoinduced charge-transfer characteristics. ■ INTRODUCTIONThe advantages of metal-free organic sensitizers, for the application in dye-sensitized solar cells (DSSCs), place them more and more into the focus of sensitizer research and development. Superior to their ruthenium-containing alternatives 1 are their extinction coefficients and the nearly unlimited possibilities of varying parameters such as the overall π-conjugation, the distance between the donor and the acceptor, and the nature of the anchoring groups by wellestablished synthetic methods.2 This allows for fine-tuning the spectral and electronic features as well as for a control over charge-transfer kinetics and electronic coupling to TiO 2 . Understanding the influence of structural variations to the sensitizer, such as the length of π-conjugation or anchoring/ acceptor group choice on the DSSC device performance, is crucial for advancing this field and technology. 3,4 Critical factors that influenced performance properties are (i) the excited-state redox potentials, which should be properly aligned with the conduction band of TiO 2 , (ii) the light-harvesting features of the sensitizer, (iii) the conjugation across the donor and anchoring groups, and (iv) the electronic coupling between the lowest unoccupied molecular orbital (LUMO) and the conduction band of the TiO 2 .5 It has been shown that a sensitive interplay between all of these fact...

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Synthetic Strategy of Low-Bandgap Organic Sensitizers and Their Photoelectron Injection Characteristics

Cited by 16 publications

References 44 publications

Organic sensitizers from D–π–A to D–A–π–A: effect of the internal electron-withdrawing units on molecular absorption, energy levels and photovoltaic performances

Organic sensitizers from D–π–A to D–A–π–A: effect of the internal electron-withdrawing units on molecular absorption, energy levels and photovoltaic performances

High‐Performance Organic Dyes with Electron‐Deficient Quinoxalinoid Heterocycles for Dye‐Sensitized Solar Cells under One Sun and Indoor Light

Position-Dependent Extension of π-Conjugation in D-π-A Dye Sensitizers and the Impact on the Charge-Transfer Properties

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