Contact potential difference and work function of organic crystals

The vibrating condenser method was applied for measurement of the contact potential difference with organic crystals. It gave work functions of reasonable values for aromatic hydrocarbon crystals. From the work function, combined with other observable parameters, an energy diagram for the crystals can be constructed, which indicates that the location of the Fermi level is slightly different from that of the intrinsic level. Supplementary experiments on the photoelectromotive force due to the Dember effect and the photovoltaic effect in violanthrene crystal, gave results consistent with the above conclusion, indicating the hole conduction.