14 Photoenergy Conversion (Dye-Sensitized Solar Cells)
525
hydrophobicity of the dyes with increasing the length of the oligothiophene linker
prevented electrolytes from approaching the NiO surface and retarded interfacial
charge recombination between the holes generated in the NiO electrode and the
I
− ions in the electrolyte (dark current). The J sc , V oc , ff , and η values drastically
increased with increasing the length of the oligothiophene linker in DYE36–38.
The NiO DSSC using DYE38 yielded a J sc value of 5.35 mA cm
−2 , a V oc value
of 218 mV, and a ff value of 0.35 under standard AM 1.5 simulated sunlight (100
mW cm
−2 ), corresponding to an η value of 0.41%, which is the highest conversion
efficiency in NiO DSSCs. Moreover, the p-type NiO DSSC based on DYE38 and
tris(1,2-diaminoethane)cobalt(II)/(III) electrolytes exhibited a high η value of 1.3%
(Powar et al. 2013).
14.6 Summary
As described in this chapter, exquisite molecular designs and synthetic strategies of
organic dye sensitizers for various types of DSSCs have been developed so far to
improve the photovoltaic performances and chemical and environmental stabilities.
Additionally, there has been a gradual accumulation of useful knowledge about the
effects of the photophysical and electrochemical properties and molecular structures
of organic dye sensitizers on the DSSC performances, which has made a considerable contribution to research and development on DSSCs. However, the fact is
that research on DSSCs using organic dyes has tended to stagnate in recent years.
Obviously, it can be pointed out that DSSCs have not yet led to sufficient solar
energy-to-electricity conversion over the wide spectral region of sunlight, i.e., from
visible light to the red/NIR region, which is the major reason for the limited photovoltaic performances of DSSCs. Thus, an effective strategy to improve the photovoltaic performances is the use of panchromatic organic dye sensitizers with intense
photoabsorption properties in the red/NIR region (600–1000 nm). We believe that the
development of type-II organic dye sensitizers with efficient light-harvesting capabilities is a key to achieving the goal and achieving a breakthrough in the practical
use of high-performance DSSCs exhibiting photosensitization over the whole region
of sunlight because type-II dye sensitizers efficiently harvest sunlight particularly in
the red region due to the DTCT band and eased restrictions on the LUMO energy
levels. Such type-II DSSCs will attract further attention from chemists, physicists,
and engineers because of the enormous scientific interest in their construction and
operational principles, and much efforts are required for the practical use and creation
of high-performance DSSCs.
525
hydrophobicity of the dyes with increasing the length of the oligothiophene linker
prevented electrolytes from approaching the NiO surface and retarded interfacial
charge recombination between the holes generated in the NiO electrode and the
I
− ions in the electrolyte (dark current). The J sc , V oc , ff , and η values drastically
increased with increasing the length of the oligothiophene linker in DYE36–38.
The NiO DSSC using DYE38 yielded a J sc value of 5.35 mA cm
−2 , a V oc value
of 218 mV, and a ff value of 0.35 under standard AM 1.5 simulated sunlight (100
mW cm
−2 ), corresponding to an η value of 0.41%, which is the highest conversion
efficiency in NiO DSSCs. Moreover, the p-type NiO DSSC based on DYE38 and
tris(1,2-diaminoethane)cobalt(II)/(III) electrolytes exhibited a high η value of 1.3%
(Powar et al. 2013).
14.6 Summary
As described in this chapter, exquisite molecular designs and synthetic strategies of
organic dye sensitizers for various types of DSSCs have been developed so far to
improve the photovoltaic performances and chemical and environmental stabilities.
Additionally, there has been a gradual accumulation of useful knowledge about the
effects of the photophysical and electrochemical properties and molecular structures
of organic dye sensitizers on the DSSC performances, which has made a considerable contribution to research and development on DSSCs. However, the fact is
that research on DSSCs using organic dyes has tended to stagnate in recent years.
Obviously, it can be pointed out that DSSCs have not yet led to sufficient solar
energy-to-electricity conversion over the wide spectral region of sunlight, i.e., from
visible light to the red/NIR region, which is the major reason for the limited photovoltaic performances of DSSCs. Thus, an effective strategy to improve the photovoltaic performances is the use of panchromatic organic dye sensitizers with intense
photoabsorption properties in the red/NIR region (600–1000 nm). We believe that the
development of type-II organic dye sensitizers with efficient light-harvesting capabilities is a key to achieving the goal and achieving a breakthrough in the practical
use of high-performance DSSCs exhibiting photosensitization over the whole region
of sunlight because type-II dye sensitizers efficiently harvest sunlight particularly in
the red region due to the DTCT band and eased restrictions on the LUMO energy
levels. Such type-II DSSCs will attract further attention from chemists, physicists,
and engineers because of the enormous scientific interest in their construction and
operational principles, and much efforts are required for the practical use and creation
of high-performance DSSCs.