B.M.Rumyantsev, V.I.Berendyaev,
B.V.Kotov
It is shown that the mechanism of charge carrier photogeneration
in sensitized and unsensitized films of polyimides (PIs) 4.4-diaminotri-phenylamine
depends on the intensity and kind (inter- or intrachain) of electron
donor-acceptor (EDA) inter action between donor (triphenyl-amine)
and acceptor (diimide) fragments of PI chain. For PIs with dominant
interchain EDA interaction the photogeneration occurs via thermal
field-assisted dissociation of ion-radical pairs (IRP) which are formed
from the excited charge transfer complexes (CTC). The photogeneration
is found to occur also in red and near IR spectral region (650-840
nm) due to photostimulation of stable Poole-Frenkel's pairs (PFP)
which are the triphenylamine cation-radicals of PI chains stabilized
by halogen anions from solvent residues or halogenhydrocarbon additive.
The metastable PFP formation and corresponding photostimulated currents
are observed in air only but not in vacuum. The sensitization process
in these PIs involves the nonradiative energy transfer from excited
dye to CTC or PFP which are photogeneration centers. For PIs with
weak interchain EDA interaction the primary act of sensitized photogeneration
is the exciplex formation of excited dye with triphenylamine polymer
fragment. For PIs with dominant intrachain EDA interaction the "threshold"
character of photogeneration quantum yield field dependence is observed
indicating the field induced transition from excited intrachain state
to IRP.