Search

The variation of the photocurrent with temperature is found to obey the relation i = i0e−E/RT in naphthalene, stilbene, diphenyl, terphenyl, β-methylanthracene, anthracene, azulene, and pyrene. The activation energies have been measured and are found to increase in the above order. These activation energies show no apparent correlation with the corresponding activation energy of semiconduction, and it is suggested they are associated with the charge carrier transport process.

The spectral response, voltage dependence, and intensity dependence of the surface photocurrent in naphthalene, terphenyl, pyrene, stilbene, and azulene have been measured. Pyrene and naphthalene have a high sensitivity for photoconduction at the long-wavelength edge of the optical absorption spectrum. In the spectral response of pyrene three peaks appear at 4475 Å, 4275 Å, and 4100 Å. It is suggested that these peaks are due to weak optical absorptions to energy levels which are highly efficient in promoting conduction. It is possible that a similar effect occurs in naphthalene, where maximum photoconductivity coincides with a weak absorption reported by McClure and Schnepp. Azulene only shows photoconductivity at wavelengths corresponding to absorption to the second singlet state.

The variation of the photocurrent and dark current on melting naphthalene and biphenyl was studied. A large increase in the value of the photocurrent was observed. This change is very similar to that of the dark current. It is concluded that the increased mobilities of the charge carriers in the melt are mainly responsible for the change in both cases. The existence of photoconduction in the non-crystalline state is discussed.