The energy structures and photoelectric behavior of sandwich-type organic photocells, configurations of which are Au/benzo[b]phenothiazine/Al, Al/dibenzo[a,h]phenothiazine/In, Al/dibenzo[a,j]phenothiazine/In, and Au/triphenodithiazine/Al, are investigated. The electrical and photovoltaic measurements show that the blocking contacts are formed at the pigments/Al interfaces in these four cells. These experimental results are consistent with the proposed energy band structures of the cells, which are estimated on the basis of the experimental results of ultraviolet photoelectron spectra and the threshold values in photocurrent action spectra.

The homogeneous electrochemical oxidations of four phenothiazine derivatives, three isomers of benzophenothiazine and triphenodithiazine, were studied in acetonitrile solution together with phenothiazine itself. Their first and second redox potentials were determined by means of cyclic voltammetry. In all the materials examined, reversible one-electron oxidations were characterized. The electrogenerated cation radicals, except for triphenodithiazine, underwent a second one-electron oxidation and, after a subsequent chemical transformation, formed the corresponding benzophenothiazinium cations. For triphenodithiazine, only the first oxidation potential was observable under our experimental conditions. The electronic states of both the intermediates and the final products of electrolytic oxidation were identified by their electronic absorption spectra and electron spin resonance absorption spectra. The values of the first oxidation potential of the benzophenothiazines were proportional to the ionization energies, which were given by molecular orbital calculations.

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Photovoltaic behaviors of evaporated thin films of triphenodioxazine (TPDO) and 6,13-dichlorotriphenodioxazine (DClTPDO) were investigated with sandwich-type cells, the configurations of which were Ag/TPDO/Al and Al/DClTPDO/indium–tin oxide (ITO). The action spectra of the short-circuit photocurrent suggest that only the photons absorbed by pigments near the Ag/TPDO interface or the DClTPDO/ITO interface are effective to produce carriers for external circuits. These results mean that Schottky barriers are formed at these interfaces, and that both pigment layers act as n-type semiconductors. Observed effects of oxygen and/or hydrogen gas on the dark conductivity of these pigment films also reflect the n-type semiconducting behavior. The observed electrical behaviors are consistent with the proposed band structures for these two cells, which are estimated from the spectroscopic data.