How efficient is electron collection in dye-sensitized solar cells? comparison of different dynamic methods for the determination of the electron diffusion length

Halina K Dunn, Laurence M Peter

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Abstract

The diffusion length of electrons in high efficiency liquid electrolyte dye-sensitized nanocrystalline solar cells has been investigated using two different approaches. The first method is based on measuring the rise and decay times of the small amplitude photovoltage increment generated by a short laser pulse superimposed on a range of steady-state illumination levels. The advantage of this technique is that it allows the simultaneous measurement of the diffusion coefficient and electron lifetime under identical conditions. In addition to transport-controlled substrate charging, direct injection of electrons into the substrate from dye adsorbed at the contact interface was observed at the high laser pulse energies required for measurements at high dc photovoltages. The second method involves using intensity-modulated photocurrent and photovoltage spectroscopies (IMPS and IMVS, respectively) to measure the electron diffusion coefficient and electron lifetime at short circuit and open circuit, respectively, as a function of light intensity. The difference between the electron trap occupancies under open-circuit and short-circuit conditions must be accounted for in this case. The diffusion lengths derived from the study are in the range of 40-70 mu m, which are at least an order of magnitude greater than the film thickness. This indicates that the electron collection efficiency in the cells is close to 100%.
Original languageEnglish
Pages (from-to)4726-4731
Number of pages6
JournalJournal of Physical Chemistry C
Volume113
Issue number11
Early online date25 Feb 2009
DOIs
Publication statusPublished - 19 Mar 2009

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electron diffusion
diffusion length
solar cells
dyes
Electrons
photovoltages
electrons
short circuits
Short circuit currents
Laser pulses
Coloring Agents
Dyes
diffusion coefficient
life (durability)
Electron traps
Networks (circuits)
Direct injection
Substrates
pulses
Photocurrents

Cite this

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title = "How efficient is electron collection in dye-sensitized solar cells? comparison of different dynamic methods for the determination of the electron diffusion length",
abstract = "The diffusion length of electrons in high efficiency liquid electrolyte dye-sensitized nanocrystalline solar cells has been investigated using two different approaches. The first method is based on measuring the rise and decay times of the small amplitude photovoltage increment generated by a short laser pulse superimposed on a range of steady-state illumination levels. The advantage of this technique is that it allows the simultaneous measurement of the diffusion coefficient and electron lifetime under identical conditions. In addition to transport-controlled substrate charging, direct injection of electrons into the substrate from dye adsorbed at the contact interface was observed at the high laser pulse energies required for measurements at high dc photovoltages. The second method involves using intensity-modulated photocurrent and photovoltage spectroscopies (IMPS and IMVS, respectively) to measure the electron diffusion coefficient and electron lifetime at short circuit and open circuit, respectively, as a function of light intensity. The difference between the electron trap occupancies under open-circuit and short-circuit conditions must be accounted for in this case. The diffusion lengths derived from the study are in the range of 40-70 mu m, which are at least an order of magnitude greater than the film thickness. This indicates that the electron collection efficiency in the cells is close to 100{\%}.",
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N2 - The diffusion length of electrons in high efficiency liquid electrolyte dye-sensitized nanocrystalline solar cells has been investigated using two different approaches. The first method is based on measuring the rise and decay times of the small amplitude photovoltage increment generated by a short laser pulse superimposed on a range of steady-state illumination levels. The advantage of this technique is that it allows the simultaneous measurement of the diffusion coefficient and electron lifetime under identical conditions. In addition to transport-controlled substrate charging, direct injection of electrons into the substrate from dye adsorbed at the contact interface was observed at the high laser pulse energies required for measurements at high dc photovoltages. The second method involves using intensity-modulated photocurrent and photovoltage spectroscopies (IMPS and IMVS, respectively) to measure the electron diffusion coefficient and electron lifetime at short circuit and open circuit, respectively, as a function of light intensity. The difference between the electron trap occupancies under open-circuit and short-circuit conditions must be accounted for in this case. The diffusion lengths derived from the study are in the range of 40-70 mu m, which are at least an order of magnitude greater than the film thickness. This indicates that the electron collection efficiency in the cells is close to 100%.

AB - The diffusion length of electrons in high efficiency liquid electrolyte dye-sensitized nanocrystalline solar cells has been investigated using two different approaches. The first method is based on measuring the rise and decay times of the small amplitude photovoltage increment generated by a short laser pulse superimposed on a range of steady-state illumination levels. The advantage of this technique is that it allows the simultaneous measurement of the diffusion coefficient and electron lifetime under identical conditions. In addition to transport-controlled substrate charging, direct injection of electrons into the substrate from dye adsorbed at the contact interface was observed at the high laser pulse energies required for measurements at high dc photovoltages. The second method involves using intensity-modulated photocurrent and photovoltage spectroscopies (IMPS and IMVS, respectively) to measure the electron diffusion coefficient and electron lifetime at short circuit and open circuit, respectively, as a function of light intensity. The difference between the electron trap occupancies under open-circuit and short-circuit conditions must be accounted for in this case. The diffusion lengths derived from the study are in the range of 40-70 mu m, which are at least an order of magnitude greater than the film thickness. This indicates that the electron collection efficiency in the cells is close to 100%.

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