HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 193
C72 - Novel NIR Sensitizers for Dye Sensitized Solar Cells
Iuliia Shcherbakova a , Marina Simeunovic a , Simone Hochleitner a , Toby Meyer b , Frederic
Ostwald b , Thomas Geiger a
a, Empa, Überlandstrasse 129, Dübendorf, 8600, CH
b, Solaronics SA, Rue de l'Ouriette 129, Aubonne VD, CH
Dye-sensitized solar cells (DSC) are important low-cost alternatives to conventional solidstate
photovoltaic devices. (1) The charge transfer sensitizers commonly applied in this type of
solar cell are ruthenium polypyridyl complexes that show a major absorption in the visible
spectrum. The spectral match of the sensitizer absorption to the solar radiation is the crucial
factor for efficient energy conversion. In this regard, development of the sensitizing dyes
converting photons to electrons in the near IR region is essential for increasing short circuit
current (Jsc). Thus, we focus on the preparation of new unsymmetrical squaraine and
heptamethine dyes, their optical, electrochemical and photovoltaic properties. These metalfree
dyes are well-known for their intense absorption in the visible and far red to NIR domain
of the solar spectrum and high molecular extinction coefficients (up to 300000 dm 3 mol -1 cm -
1 ). (2,3)
A number of unsymmetrical squaraine and heptamethine dyes with different heterocyclic
moieties were synthesized using a building block technique. Introduction of a new quinoline
anchor group in the squaraine and heptamethine dye structures shifts bathochromic the
absorption peak to over 700 nm. Especially, UV-vis investigations of the unsymmetrical dyes
impressively demonstrate the great spectral diversity above 700 nm. Exemplarily, the UV-vis
spectra of the dyes in solution and the spectrum of the Sun's solar radiation (AM1.5) are
shown in Fig. 1.
Figure 1 UV-vis spectra of the novel NIR sensitizing dyes in chloroform and the spectrum of the Sun's solar radiation
(AM1.5).
Finally, the unsymmetrical heptamethine and squaraine dyes were tested in laboratory dye
sensitized spot cells (glas/FTO/TiO2/dye/iodid-triiodid(acetonitril)/Pt/FTO/glas) with an active
area of 0.72 cm 2 . Optimized dye sensitized solar cell showed a short circuit current density (Jsc)
of 3.47 mAcm -2 , an open circuit voltage (Voc) of 495 mV and a fill factor (ff) of 0.76 leading to an
overall conversion efficiency η of 1.31% in case of the heptamethine dye (Hepta12) and a short
circuit current density (Jsc) of 7.54 mAcm -2 , an open circuit voltage (Voc) of 520 mV and a fill
factor (ff) of 0.71 leading to an overall conversion efficiency η of 2.78% for the squaraine dye
(SQQ3) obtained under 1000 Wm -2 illumination intensity. Remarkably, dye sensitized solar
© SEFIN 2012