Electrodeless Determination of Charge Carrier Mobility in Poly(3-hexylthiophene) Films Incorporating Perylenediimide as Photoconductivity Sensitizer and Spectroscopic Probe

The charge carrier mobility and its generation efficiency in regioregular and regiorandom poly(3-hexylthiophene) (P3HT) films upon exposure to light pulses are studied by flash-photolysis time-resolved microwave conductivity and transient absorption spectroscopy. For the full experimental determination of alternating current mobility without electrodes, we incorporated a perylenecarboxydiimide (PDI) derivative into the films not only to increase the photoconductivity but also estimate the quantum efficiency of charge generation by kinetic tracing of PDI radical anions. We discuss the mobility, quantum efficiency, decay of charge carriers, and film morphology observed by an X-ray diffraction and an atomic force microscope with various PDI concentrations. It is found that the three-dimensional mobility mainly attributed to the positive charges on regioregular P3HT is decreased from 0.12 to 0.070 cm(2)/Vs by addition of PDI which disturbs the intermolecular pi-stacking, while that on regiorandom P3HT shows an almost constant value of 0.006 cm(2)/Vs. The quantum efficiency in regioregular P3HT reveals a peak at 6 mol % PDI for 355-nm excitation. The reason for the appearance of the peak is examined by changing excitation wavelength and inspecting the steady-state absorption and fluorescence spectra. The methodology and findings obtained by utilizing the additive as both an acceptor and a probe is proved to be useful for the investigations on optoelectronic properties of wide varieties of organic semiconductors.