Interfacial hole traps in conjugated polymer thin films

PHYS 487

Kwang-Jik Lee, tigerjik@mail.utexas.edu1, Leonid Fradkin, leonid_fradkin@mail.utexas.edu1, and Paul F. Barbara, P.barbara@mail.utexas.edu2. (1) Center for Nano and Molecular Science and Technology, The University of Texas at Austin, Austin, TX 78712, (2) Department of Chemistry and Biochemistry and the Center for Nano- and Molecular Science and Technology, University of Texas, Austin, TX 78712
We studied the processes of charging and discharging in semiconductor conjugated polymer thin films. The Fluorescence-Voltage Time Resolved (FV-TR) spectroscopy was applied on poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(2,5-bis(2'-ethyl-hexyl)-1,4-phenylenevinylene) (BEH-PPV). The photogenerated carriers in the device were found to play a dominant role in the fluorescence quenching mechanism. The evidence of a relatively slow discharging rate suggests trapping of holes in deep trap sites in the polymers. We show that the presence of oxygen in the device strongly affects the device characteristics. Aged samples demonstrate more fluorescence quenching at positive biases than freshly prepared. We believe that the candidate for the photobleached form of the polymer is F8BT+/anion complex. Such a complex could be formed by photoinduced electron transfer between F8BT and oxygen forming F8BT+/O2-.

Both processes of charging and discharging of the device were found to be bias dependant. However, we show that the presence of light (laser excitation) is required for more efficient hole-injection and discharging of the device.

 

PHYS Poster Session - Nanostructured Materials and Nanophotonics
7:30 PM-10:00 PM, Wednesday, April 9, 2008 Morial Convention Center -- Hall A, Poster

Division of Physical Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008