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Ultrafast charge separation dynamics in opaque, operational dye-sensitized solar cells revealed by femtosecond diffuse reflectance spectroscopy.

Ghadiri E, Zakeeruddin SM, Hagfeldt A, Grätzel M, Moser JE - Sci Rep (2016)

Bottom Line: This observation is significantly different from what was reported in the literature where the electron-hole back recombination for transparent films of small particles is generally accepted to occur on a longer time scale of microseconds.The kinetics of the ultrafast electron injection remained unchanged for voltages between +500 mV and -690 mV, where the injection yield eventually drops steeply.The primary charge separation in Y123 organic dye based devices was clearly slower occurring in two picoseconds and no kinetic component on the shorter femtosecond time scale was recorded.

View Article: PubMed Central - PubMed

Affiliation: Photochemical Dynamics Group , Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.

ABSTRACT
Efficient dye-sensitized solar cells are based on highly diffusive mesoscopic layers that render these devices opaque and unsuitable for ultrafast transient absorption spectroscopy measurements in transmission mode. We developed a novel sub-200 femtosecond time-resolved diffuse reflectance spectroscopy scheme combined with potentiostatic control to study various solar cells in fully operational condition. We studied performance optimized devices based on liquid redox electrolytes and opaque TiO2 films, as well as other morphologies, such as TiO2 fibers and nanotubes. Charge injection from the Z907 dye in all TiO2 morphologies was observed to take place in the sub-200 fs time scale. The kinetics of electron-hole back recombination has features in the picosecond to nanosecond time scale. This observation is significantly different from what was reported in the literature where the electron-hole back recombination for transparent films of small particles is generally accepted to occur on a longer time scale of microseconds. The kinetics of the ultrafast electron injection remained unchanged for voltages between +500 mV and -690 mV, where the injection yield eventually drops steeply. The primary charge separation in Y123 organic dye based devices was clearly slower occurring in two picoseconds and no kinetic component on the shorter femtosecond time scale was recorded.

No MeSH data available.


Related in: MedlinePlus

Comparison of the kinetics observed in the Y123 sensitized TiO2 film at different wavelength regions of 690 nm and 740 nm and Y123 molecular structure.(a) Transient absorptance of Y123 sensitized TiO2 films at 690 nm (green) and 740 nm (blue). The formation of the blue trace measured at 740 nm, which reflects the electron injection time, is occurring in picosecond time scale and is fitted with an exponential growth function with a time constant of 1.1 ps. (b) Y123 molecular structure and schematic of electron transfer processes. Blue arrow shows the electron injection process.
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f8: Comparison of the kinetics observed in the Y123 sensitized TiO2 film at different wavelength regions of 690 nm and 740 nm and Y123 molecular structure.(a) Transient absorptance of Y123 sensitized TiO2 films at 690 nm (green) and 740 nm (blue). The formation of the blue trace measured at 740 nm, which reflects the electron injection time, is occurring in picosecond time scale and is fitted with an exponential growth function with a time constant of 1.1 ps. (b) Y123 molecular structure and schematic of electron transfer processes. Blue arrow shows the electron injection process.

Mentions: Figure 8 compares the kinetics of a Y123 sensitized TiO2 film probed in two different wavelength regions of 690 nm and 740 nm. According to Fig. 7a, at 690 nm the excited-state of Y123 has absorption while at 740 nm the excited-state does not absorb. Therefore, the blue trace in Fig. 8 recorded at 740 nm, represents a pure monitoring of the kinetics of the electron injection process. The formation of the signal, which reflects the electron injection time, is occurring in picosecond time scale and is fitted with an exponential growth function with a time constant of 1.1 ps. As a result, we observe that in the Y123 D-π-A dye, the charge injection kinetics is not as fast as in Ru-based dyes, as reported by Chergui and co-workers28.


Ultrafast charge separation dynamics in opaque, operational dye-sensitized solar cells revealed by femtosecond diffuse reflectance spectroscopy.

Ghadiri E, Zakeeruddin SM, Hagfeldt A, Grätzel M, Moser JE - Sci Rep (2016)

Comparison of the kinetics observed in the Y123 sensitized TiO2 film at different wavelength regions of 690 nm and 740 nm and Y123 molecular structure.(a) Transient absorptance of Y123 sensitized TiO2 films at 690 nm (green) and 740 nm (blue). The formation of the blue trace measured at 740 nm, which reflects the electron injection time, is occurring in picosecond time scale and is fitted with an exponential growth function with a time constant of 1.1 ps. (b) Y123 molecular structure and schematic of electron transfer processes. Blue arrow shows the electron injection process.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837338&req=5

f8: Comparison of the kinetics observed in the Y123 sensitized TiO2 film at different wavelength regions of 690 nm and 740 nm and Y123 molecular structure.(a) Transient absorptance of Y123 sensitized TiO2 films at 690 nm (green) and 740 nm (blue). The formation of the blue trace measured at 740 nm, which reflects the electron injection time, is occurring in picosecond time scale and is fitted with an exponential growth function with a time constant of 1.1 ps. (b) Y123 molecular structure and schematic of electron transfer processes. Blue arrow shows the electron injection process.
Mentions: Figure 8 compares the kinetics of a Y123 sensitized TiO2 film probed in two different wavelength regions of 690 nm and 740 nm. According to Fig. 7a, at 690 nm the excited-state of Y123 has absorption while at 740 nm the excited-state does not absorb. Therefore, the blue trace in Fig. 8 recorded at 740 nm, represents a pure monitoring of the kinetics of the electron injection process. The formation of the signal, which reflects the electron injection time, is occurring in picosecond time scale and is fitted with an exponential growth function with a time constant of 1.1 ps. As a result, we observe that in the Y123 D-π-A dye, the charge injection kinetics is not as fast as in Ru-based dyes, as reported by Chergui and co-workers28.

Bottom Line: This observation is significantly different from what was reported in the literature where the electron-hole back recombination for transparent films of small particles is generally accepted to occur on a longer time scale of microseconds.The kinetics of the ultrafast electron injection remained unchanged for voltages between +500 mV and -690 mV, where the injection yield eventually drops steeply.The primary charge separation in Y123 organic dye based devices was clearly slower occurring in two picoseconds and no kinetic component on the shorter femtosecond time scale was recorded.

View Article: PubMed Central - PubMed

Affiliation: Photochemical Dynamics Group , Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.

ABSTRACT
Efficient dye-sensitized solar cells are based on highly diffusive mesoscopic layers that render these devices opaque and unsuitable for ultrafast transient absorption spectroscopy measurements in transmission mode. We developed a novel sub-200 femtosecond time-resolved diffuse reflectance spectroscopy scheme combined with potentiostatic control to study various solar cells in fully operational condition. We studied performance optimized devices based on liquid redox electrolytes and opaque TiO2 films, as well as other morphologies, such as TiO2 fibers and nanotubes. Charge injection from the Z907 dye in all TiO2 morphologies was observed to take place in the sub-200 fs time scale. The kinetics of electron-hole back recombination has features in the picosecond to nanosecond time scale. This observation is significantly different from what was reported in the literature where the electron-hole back recombination for transparent films of small particles is generally accepted to occur on a longer time scale of microseconds. The kinetics of the ultrafast electron injection remained unchanged for voltages between +500 mV and -690 mV, where the injection yield eventually drops steeply. The primary charge separation in Y123 organic dye based devices was clearly slower occurring in two picoseconds and no kinetic component on the shorter femtosecond time scale was recorded.

No MeSH data available.


Related in: MedlinePlus