Organic Photoconductors. IV. Sign of the Charge Carrier

If the energies of carriers in the conduction band and valence band of a dye can be determined with respect to the corresponding levels in cadmium sulfide, then the sign and magnitude of the photo-emf developed at a junction between dye and cadmium sulfide can often be interpreted as indicating a transfer of carriers between conduction bands, conduction hence being due primarily to electrons; or as a transfer between valence bands, conduction thus being due to holes. In this way the majority carrier in several cationic dyes is shown to be electrons; in erythrosin, an anionic dye, holes; and in methyl chlorophyllide-a, a non-ionic dye, probably electrons.