CPM Seminar

Laser Photoelectron Spectroscopy of an Organic Polymer Semiconductor

J. Todd Stuckless

Chemistry Department
University of British Columbia

We irradiate a conjugated polymer with a high-intensity laser pulse, and probe its excited states by photoelectron spectroscopy using a second photon in the same pulse. This technique might become a valuable complement to the classic work done using pump-probe transient absorption spectroscopies. It has the advantage of directly providing energy values relative to the vacuum and Fermi levels, which is important in electronic device application. Our results for emission yield versus photon flux in polythiophene shows the roll-over in excited-state concentration which organic semiconductors are prone to. The data is consistent with kinetic modeling of the excited state as polaronic charge-carriers. The energy distribution of electrons emitted from calcium doped samples, shows a peak in emission from states pinned above the Fermi level while the vacuum level bends. This effect had previously been observed in studies of polaron formation in molecular semiconductors, by use of the inverse photoelectron technique. Polarons have a strong non-coulombic interaction which leads to complex behavior in band-bending of the energy levels, making experimental measurements crucial.