Limits...
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

Transient white light continuum absorbance spectrum.(a) Y123 dye measured in solution and (b) Y123 sensitized TiO2 transparent film, in the visible light wavelength region. Excitation intensities are 300 nJ/ pulse for films and 1000 nJ/pulse for measurement in solution. Measurements in solution are performed under N2 bubbling.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4837338&req=5

f7: Transient white light continuum absorbance spectrum.(a) Y123 dye measured in solution and (b) Y123 sensitized TiO2 transparent film, in the visible light wavelength region. Excitation intensities are 300 nJ/ pulse for films and 1000 nJ/pulse for measurement in solution. Measurements in solution are performed under N2 bubbling.

Mentions: In order to study the mechanism of the very fast decay of the signal in 2 ps, we performed the transient broadband absorption measurements. We compared the broadband transient absorption of Y123-sensitized TiO2 film with that of Y123 dye in solution as a reference sample where interfacial electron transfer process is deactivated. By comparison of the recorded spectra of the dye-sensitized films with the dye in solution we can clearly resolve the spectral absorption contribution of the excited-state and oxidized state of the Y123 dye. The transient absorption spectra of the samples measured at NIR region is also shown in Supplementary Figure S11. The ground state optical absorption spectrum of the dye is provided in Supplementary Figure S8. For the dye in solution (Fig. 7a), the negative peak at the characteristic ground state absorption of the dye around 520 nm, is attributed to the ground state bleaching of the dye formed upon photo-excitation. In Fig. 7a, a positive transient absorption is observed in the wavelength region from 630 nm up to 700 nm. This transition is assigned to excited-state absorption of dye molecule. The dye excited-state relaxation time constant is 52 ps and has a mirror-like kinetics to ground state relaxation. The transient absorbance spectrum of the dye-sensitized TiO2 films is presented in Fig. 7b. In this sample, the ground state bleaching is observed at 580 nm, which is around 60 nm shifted with respect to the steady-state absorption onset of the dye.


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)

Transient white light continuum absorbance spectrum.(a) Y123 dye measured in solution and (b) Y123 sensitized TiO2 transparent film, in the visible light wavelength region. Excitation intensities are 300 nJ/ pulse for films and 1000 nJ/pulse for measurement in solution. Measurements in solution are performed under N2 bubbling.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f7: Transient white light continuum absorbance spectrum.(a) Y123 dye measured in solution and (b) Y123 sensitized TiO2 transparent film, in the visible light wavelength region. Excitation intensities are 300 nJ/ pulse for films and 1000 nJ/pulse for measurement in solution. Measurements in solution are performed under N2 bubbling.
Mentions: In order to study the mechanism of the very fast decay of the signal in 2 ps, we performed the transient broadband absorption measurements. We compared the broadband transient absorption of Y123-sensitized TiO2 film with that of Y123 dye in solution as a reference sample where interfacial electron transfer process is deactivated. By comparison of the recorded spectra of the dye-sensitized films with the dye in solution we can clearly resolve the spectral absorption contribution of the excited-state and oxidized state of the Y123 dye. The transient absorption spectra of the samples measured at NIR region is also shown in Supplementary Figure S11. The ground state optical absorption spectrum of the dye is provided in Supplementary Figure S8. For the dye in solution (Fig. 7a), the negative peak at the characteristic ground state absorption of the dye around 520 nm, is attributed to the ground state bleaching of the dye formed upon photo-excitation. In Fig. 7a, a positive transient absorption is observed in the wavelength region from 630 nm up to 700 nm. This transition is assigned to excited-state absorption of dye molecule. The dye excited-state relaxation time constant is 52 ps and has a mirror-like kinetics to ground state relaxation. The transient absorbance spectrum of the dye-sensitized TiO2 films is presented in Fig. 7b. In this sample, the ground state bleaching is observed at 580 nm, which is around 60 nm shifted with respect to the steady-state absorption onset of the dye.

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