Influence of gas molecules on the charge carrier mobility in thin films of semiconducting perylene tetracarboxylic imides

Thin films (30nm) of crystalline N,N′-dimethylperylene-3,4,9,10-biscarboximide (MePTCDI) or amorphous 1,6,7,12-tetrachloro-N,N′-dimethylperylene-3,4,9,10-biscarboximide (Cl4MePTCDI) were prepared by physical vapor deposition and characterized by conductivity and field effect measurements at pristine films and under increasing partial pressure of oxygen, ethanol, acetone, or n-butane. Changes in the conductivity of the films were observed. Field effect measurements served to differentiate between changes in the charge carrier mobility μ and changes of the charge carrier concentration n. μ was found to decrease significantly, whereas rather small changes were found in n. Gas molecules that diffused into the films changed μ at least ten times more efficiently than those molecules just adsorbed on the surface.