Hole Photoconductivity in Ferrocene, Triphenylamine, and Trans-Stilbene

The drift mobility of holes in single crystals of ferrocene, triphenylamine, and trans-stilbene has been measured by the method of transient photoconductivity. At 20°C the mobilities are: ferrocene, 2.2×10—2 cm2/V·sec; triphenylamine, 2×10—2 cm2/V·sec; and trans-stilbene, 2.4 cm2/V·sec. In trans-stilbene, the hole mobility decreases slightly with increasing temperature in the range of 100° to —50°C. In ferrocene and triphenylamine, the mobility increases with increasing temperature, but not in a manner that suggests hole motion by a thermally activated, hopping-type motion. The photoconductive excitation spectra in these solids follow the optical absorption of the exciton states built from the π and π* states of the molecules.