HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 171
C53 - The Photochemistry and Photovoltaic Performance of a New Class of Pan-
Chromatic, Donor-Acceptor Sensitizers in p-Type Dye-Sensitized Solar Cells
James M Gardner a , Jonas Petersson a , Julien Warnan b , Yann Pellegrin b , Errol Blart b , Fabrice
Odobel b , Leif Hammarström a
a, Dept. of Chemistry - Ångström, Uppsala University, Regementsvägen 1, Uppsala, 75237, SE
b, Faculté des Sciences et des Techniques de Nantes, 2 rue de la Houssinière, Nantes, 44322, FR
c, Div. of Appl. Phys. Chem.; Dept. of Chemistry, KTH, Teknikringen 30, Stockholm, 10044, SE
Efforts to utilize greater fractions of the solar spectrum have resulted in the design of a
series of three p-type sensitizers based on Squaraine. The incorporation of additional subunits
generated sensitizers with broad absorbances throughout the NIR and visible, and in
addition produced electron donating and accepting groups that promoted electron transfer
and reduced interfacial charge recombination. The electron and energy transfer dynamics for
these three novel sensitizers were studied by fs- to ms- transient absorption spectroscopy on
mesoporous nickel oxide (NiO) thin films. The three sensitizers (NDI-PMI-Sq, PMI-Sq, and Sq)
were as well utilized in complete dye-sensitized solar cells and a correlation was established
between the charge-transfer dynamics and the performance in p-type dye-sensitized solar cells
(DSCs).
Both PMI-Sq and NDI-PMI-Sq contained multiple light absorbing sub-units. The efficiency of
charge injection from each sub-unit was probed by selective excitation of each sub-unit. From
this, an excitation wavelength dependence on charge injection and intramolecular electronic
coupling was established. For all three of the sensitizers, the electron transfer events were
mapped from the initial light absorption, to intramolecular charge-transfer, to charge-injection
into NiO, and finally to interfacial charge recombination.
Figure 1 Light absorption by three novel p-type sensitizers (NDI-PMI-Sq, PMI-Sq, and Sq) results in intramolecular
charge-transfer, hole injection, and gradual interfacial recombination. The molecular design leads to long-lived
charge separation and a broad absorbance in the visible and NIR, which translates into dramatic increases in solar
cell performance.
The highest performing sensitizer was NDI-PMI-Sq, for which an exceptionally long
interfacial charge-separation was maintained (~350 μs). The time scale of charge separation
resulted in efficiencies for solar cells that were more than an order of magnitude larger than
for Sq or PMI-Sq when matched with a cobalt trisbipyridine redox couple. The implications for
the design of future pan-chromatic sensitizers will also be discussed.
© SEFIN 2012