Dresden 2009 – wissenschaftliches Programm
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SYOP: Symposium Organic Photovoltaics: From Single Molecules to Devices
SYOP 5: Organic Photovoltaics III
SYOP 5.2: Vortrag
Freitag, 27. März 2009, 10:45–11:00, ZEU 222
Bipolar substituted spiro-bifluorenes for organic solar cells? — •Cornelia M. Brendel1, Fernando Dias2, Andy P. Monkman2, and Josef Salbeck1 — 1Macromolecular Chemistry and Molecular Materials, University of Kassel, Heinrich-Plett-Strasse 40, 34132 Kassel, Germany — 2Durham Photonic Materials Institute, Department of Physics, Durham University, South Road, Durham DH1 3LN, U.K.
Substituted spiro-bifluorenes are frequently being employed in optoelectronical devices due to their tendency to build amorphous layers. Donor-acceptor compounds with a spiro-bifluorene unit as bridge have already been employed in phototransistors and have potential for application in organic solar cells.
To test their suitability for organic solar cells and clarify the role bipolar substituted spiro-bifluorenes play in phototransistors we investigated these compounds more closely by spectroscopic methods. Bipolar substituted spiro-bifluorenes show strong solvatochromism of about 100 nm when cyclohexane is exchanged by more polar solvents, e. g. methyl-THF or acetone, indicating charge-transfer emission. Charge separation by photoexcitation happens within some hundred picoseconds and has a lifetime of up to 50 ns.
We will discuss the interplay of the locally excited and the charge-transfer state on the basis of temperature dependent measurements of fluorescence and absorption as well as measurements of the fluorescence lifetime. We will also go into detail about the origin of triplett emission and its connection with the charge transfer state.