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Inner-Sphere Electron-Transfer Single Iodide Mechanism for Dye Regeneration in Dye-Sensitized Solar Cells

Jeon, Jiwon and Goddard, William A., III and Kim, Hyungjun (2013) Inner-Sphere Electron-Transfer Single Iodide Mechanism for Dye Regeneration in Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 135 (7). pp. 2431-2434. ISSN 0002-7863. doi:10.1021/ja311714a.

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During the regeneration of the oxidized dye in dye-sensitized solar cells, the redox couple of I^–/I3^– reduces the photo-oxidized dye. The simplest mechanism would be a direct charge-transfer mechanism from I^– to D^+ [D^+ + I^– → D0 + I], called the single iodide process (SIP). However, this is an unfavorable equilibrium because the redox potential of I^•/I^– is 1.224 V vs SHE, which is 0.13 V higher than that of the dye. This led to the postulation of the two iodide process (TIP) [(D^+···I^–) + I^– → (D···I^(-)_(2)) → D^0 + I^(-)_(2))] for a sufficiently high reducing power, but TIP is not consistent with either the recent experimental data suggesting the first-order kinetics or recent time-resolved spectroscopic measurements. To resolve this conundrum, we used quantum mechanics including Poisson–Boltzmann solvation to examine the electron-transfer process between I^– and D^+ for the Ru(dcb)_(2)NCS_2 or N3 dye. We find that I^– is attracted to the oxidized dye, positioning I^– next to the NCS. At this equilibrium position, the I^– electron is already 40% transferred to the NCS, showing that the redox potential of I^– is well matched with the dye. This matching of the redox potential occurs because I^– is partially desolvated as it positions itself for the inner-sphere electron transfer (ISET). The previous analyses all assumed an outer-sphere electron-transfer process. Thus our ISET-SIP model is consistent with the known redox potentials and with recent experimental reports. With the ISET-SIP mechanism, one can start to consider how to enhance the dye regeneration kinetics by redesigning ligands to maximize the interaction with iodide.

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Goddard, William A., III0000-0003-0097-5716
Additional Information:© 2013 American Chemical Society. Received: November 30, 2012; Published: February 5, 2013. This work is supported by the World Class University program (R31-2008-000-10055-0) funded by the Ministry of Education, Science and Technology of Korea.
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Ministry of Education, Science and Technology of Korea World Class University programR31-2008-000-10055-0
Issue or Number:7
Record Number:CaltechAUTHORS:20130405-104115918
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Official Citation:Inner-Sphere Electron-Transfer Single Iodide Mechanism for Dye Regeneration in Dye-Sensitized Solar Cells Jiwon Jeon, William A. Goddard, III, and Hyungjun Kim Journal of the American Chemical Society 2013 135 (7), 2431-2434
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37785
Deposited By: Jason Perez
Deposited On:05 Apr 2013 21:47
Last Modified:09 Nov 2021 23:31

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