Sensitization in the Photoconductance of Poly-N-vinylcarbazole

The sensitization in photoconductive poly-N-vinylcarbazole was studied systematically. The sensitizers were conveniently divided into two types, optical and chemical. The optical sensitization occurs with a smaller content of a dye, which extends the photoconductivity spectrum to its absorption band. Effective optical (or dye) sensitizers are found to be themselves photoconductive and n-type cationic and to have a slow photoresponse. The chemical sensitization occurs through the formation of a charge transfer complex with a considerable amount of a Lewis acid. The simultaneous addition of optical and chemical sensitizers induces amplified or additive effects; an amplified effect is observed when a strong acid is employed as a chemical sensitizer. A sensitized system with a strong acid shows a very slow photoresponse and may have fairly deep traps which act as a cause of the memory effect.