Carrier photogeneration processes in layered organic systems incorporating bisazo pigment: Xerographic and electroabsorption study

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Abstract
The role of the photoexcited state of an azo pigment as a reactant for photocarriers in a layered organic system was investigated using 2,6-anthraquinone bisazo (ABHN) or 1,4-distyrylbenzene bisazo (PDHN) pigment. Both bisazo pigments are highly sensitized by carrier transport molecules involved in the layered device. However, photocarrier generation in the bisazo pigments was quite different in the absence of sensitizing molecules; ABHN never generates, but PDHN generates to some degree by itself. The photocarriers are known to be generated via excitons of the azo pigments in the layered systems from the result of excitation-energy-independent quantum efficiencies. Electromodulated absorption spectra show that ABHN forms a Frenkel exciton and PDHN a charge-transfer-natured exciton. The different types of excitons explain the difference in carrier generation pathways of the optoelectronic systems based on these two azo pigments well.