HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 49
B14 - DFT/TDDFT computational investigation of Ru(II) and Os(II) panchromatic dye
sensitizers
Simona Fantacci , Maria Grazia Lobello, Filippo De Angelis
Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), via Elce di Sotto n. 8, Perugia, 6123, IT
A new and bright interest has been addressed towards the Ru(II) panchromatic dyes as
sensitizers in Dye-sensitized Solar Cells (DSCs). These dyes show a broad absorption of light
ranging the entire visible region up to near-IR and the idea is to exploit the extended light
harvesting for enhancing the DSC efficiency. Black Dye, [Ru(H3tcterpy)(NCS)3] - (tcterpy=4,4’,4”tricarboxy-2,2’:6’,2”-terpyridine),
despite to be one of the first panchromatic dyes employed in
DSC, 1,2 is still widely investigated, since only a deepened comprehension of its acid-base
chemistry, its photophysics and photochemistry allow to design new panchromatic dyes with
specific target functionalities.
Here the results obtained in an extensive Density Functional Theory (DFT) and Time
Dependent DFT study on Black Dye (BD) and analogous panchromatic dyes are presented. BD
and its possible deprotonated formshave been investigated with the aim to understand and
rationalize their acid-base, electrochemical and optical properties and finally to define a
relationship between these properties and the dye-sensitized solar cell (DSC) working
efficiency parameters.
Figure 1 Comparison between the theoretical and experimental absorption spectrum. Optimized geometry of
BD@TiO2.
The pKa associated to the stepwise deprotonation of the dye carboxylic groups have been
calculated, assigning the deprotonation order. The ground and excited state oxidation
potentials have been evaluated and compared to the available experimental data. The
influence of deprotonation on the absorption and emission processes has been analyzed and
the spectral changes as a function of the pH have been assigned. The adsorption geometry of
the BD with extended TiO2 models is presented, along with a detailed analysis of the excited
states energy and localization at the dye/semiconductor interface.
Calculations with inclusion of the spin-orbit coupling have been performed on BD and on
the analogous Os-dye. Our results suggest a minor role of singlet-triplet excitation in the light-
© SEFIN 2012