Optical characterization of chemically doped thin films of poly(p-phenylene vinylene)

Films of precursor route poly(p-phenylene vinylene) (PPV) have been doped by immersion in FeCl3 solution. The conductivity changes by ca. seven orders of magnitude upon doping and the photoluminescence is quenched. Investigations by photothermal deflection spectroscopy (PDS) have shown the development of broad subbandgap absorption in the spectral range 1.5–2.2 eV and at ca. 0.6 eV upon doping. Similar absorption bands have been detected also for doping with InCl3. The results for undoped samples have shown that the surface of the undoped films is a source of a featureless subgap absorption. The changes in the Raman and infrared spectra with the doping have been investigated. The similarity with the results for films doped with other dopants suggests that the changes are due to transformations of the polymer chains and are independent on the nature of the dopant. It has been shown that the used doping process leads to nonuniform doping of the films. The nonuniformity depends on the film thickness and the concentration of the solution as well.