Carbazole Dyes Research Articles

Substituted carbazole dyes for efficient molecular photovoltaics: long electron lifetime and high open circuit voltage performance

We designed and synthesized new substituted carbazole dyes, MK-14 and -16, for dye-sensitized solar cells (DSSCs) employing the I−/I3−redox couple. By the addition of a hexyloxyphenyl substituent to previously reported carbazole dyes MK-1 and -2, the electron lifetime and open circuit voltage of the DSSCs employing these dyes were increased, showing comparable values with those using a conventional Ru complex dye. This result was achieved by the retardation of the charge recombination, caused by more effective blocking of the I3− ion in the electrolyte than that in the cases of MK-1 and -2. The result shows the importance of the position of alkyl chains attached to the main framework of dye molecules.

Long-term stability of organic–dye-sensitized solar cells based on an alkyl-functionalized carbazole dye

We investigated the long-term stability of performance for dye-sensitized solar cells (DSSCs) based on an alkyl-functionalized carbazole dye (MK-2) and used in conjunction with ionic liquid-based electrolytes. We observed good long-term stability of the performance of the DSSCs during 60 days under visible-light irradiation at ca. 50 °C. The performance of the DSSC decreased gradually under white-light irradiation including UV light or at 80 °C under dark conditions. However, no decomposition or detachment of the dye molecule from the TiO2electrode was observed after these measurements. These results indicate that the MK-2dye molecule in the cell was stable even under white-light irradiation and at 80 °C under dark conditions.

Hexylthiophene-Functionalized Carbazole Dyes for Efficient Molecular Photovoltaics: Tuning of Solar-Cell Performance by Structural Modification

Novel organic dyes (MK dyes), which have a carbazole derivative as an electron donor and a cyanoacrylic acid moiety (═C(—C≡N)COOH) as an electron acceptor and an anchoring group, connected with n-hexyl-substituted oligothiophenes as a π-conjugated system, were designed and synthesized for application in dye-sensitized solar cells (DSSCs), which are one of the promising molecular photovoltaics. The photovoltaic performance of the DSSCs based on MK dyes markedly depends on the molecular structure of the dyes in terms of the number and position of n-hexyl chains and the number of thiophene moieties. Retardation of charge recombination caused by the existence of n-hexyl chains linked to the thiophene groups resulted in an increase in electron lifetime. As a consequence, an improvement of open-circuit photovoltage (Voc) and hence the solar-to-electric power conversion efficiency (η) of DSSCs was achieved upon addition of n-hexyl chains to the thiophene groups. In addition, the adsorption condition (amount of dye molecules and/or dye aggregate thickness) on the nanoporous TiO2 electrode, depending on the number of hexyl chains, strongly affected the performance of DSSCs. A larger amount and/or thicker aggregate of dye molecules brought about longer electron lifetime, which resulted in higher Voc, and slower diffusion of I3− ions in the nanoporous TiO2 electrode, which led to lower short-circuit photocurrent (Jsc) and fill factor (FF). In the result of thorough investigation on the series of MK dyes, a DSSC based on MK-2 consisting of n-hexyl-substituted quarter-thiophene produced 8.3% of η (Jsc = 15.22 mA cm−2, Voc = 0.73 V, and FF = 0.75) under 100 mW cm−2 simulated AM1.5G solar irradiation.

Progress in Fully Functionalized Photorefractive Materials

AbstractPhotorefractive (PR) materials are multifunctional materials which combine both photoconductivity and electro-optic response to show a new phenomenon: reversible modulation of the index of refraction by light. In the past years, our group has focused on the development of fully functionalized polymers, oligomers and small molecular materials. We have had success in identifying new materials and in gaining understanding in design principles of better materials. Several new PR material systems have been explored, including conjugated PR polymers containing transition metal complexes as photosensitizers, oligothiophene based PR systems and small molecular PR materials containing carbazole and methine dyes. Large net optical gain and minimized phase separation were achieved. The correlation between molecular structure and physical properties is the focal point of this paper.

A new family of amorphous molecular materials showing large photorefractive effect

A novel series of amorphous molecular materials containing carbazole and methine dyes have been synthesized and characterized for photorefractive applications.

The Action of Light on Cellulose dyed with Vat Dyes

The tendering activity of thirty–eight vat dyes has been examined by various tests, and an attempt made to discover from the constitutions of the dyes which substituents are responsible for tendering or non–tendering properties.It is found that most of the anthraquinone–carbazole dyes tested are non–tendering. The tests on other groups of dyes show that certain substituents appear to exert a tendering influence and others a protective action. It seems that the simpler chemical compounds of the vat dye series have an inherent tendering action, which is repressed or enhanced by the nature and orientation of the substituents and the resulting configuration. It therefore seems unlikely that any general rule of tendering based on the chemical constitution of the dyes can be given.A difficulty in estimating the relation of constitution to tendering is the impossibility of comparing dyes of different light absorption, since the light energy depends on the wavelength.It is also found that both oxidation and reduction phenomena can be brought about by irradiating cotton dyed with vat dyes. This result confirms earlier suggestions that the tendering reaction may be caused by a succession of reducing and oxidising processes.