Time-resolved Spectroscopic Study on Photocarrier Generation Process in Layered Organic Photoconductors

Abstract

As a model for electron processes in organic thin films, carrier generation after photoexcitation of organic photoconductors was studied by the time-resolved infrared spectroscopy. A broad transient absorption was observed in the IR range after a photocarrier generation. We ascribed all these transients to the cationic species of a charge transport material (CTM) from the results of the measurements in various conditions. The transient absorption spectrum showed remarkable dependence on the CTM concentration. From this observation, we concluded that the cationic species of CTMs were monomer, dimer and larger aggregate cations. The latter two cationic species are regarded as the holes delocalized within some CTM molecules. Based on these observations, carrier generation mechanism in organic photoconductors is discussed.