The controlled adjustment of the conductivity of molecular organic semiconductors is essential for their technical application. As the n-type organic semiconductor perylene-3,4,9,10-tetracarboxylicdianhydride ͑PTCDA͒ is known to be n doped by alkali metals, pristine and sodium doped PTCDA was chosen as a model system to investigate the charge carrier generation and transport in organic semiconductors. Temperaturedependent conductivity measurements were performed to obtain information about the transport mechanism. Measurement of the thermoelectric force, i.e., the Seebeck coefficient, gives a closer insight into the energy levels, participating in charge carrier generation. Based on the performed measurements a model for charge carrier transport in pristine and in alkali metal doped PTCDA is suggested.

In order to clarify the doping behavior of different alkali metals in perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), Fourier transform infrared spectra of PTCDA thin films doped with sodium, potassium, and cesium were measured and compared. Furthermore the vibrational properties were calculated using density-functional theory and these calculated vibrational frequencies were assigned to the experimental IR modes of the thin films.