Photoconducting polymer nanocomposites with efficient photogeneration and bipolar transport for optoelectronic applications

Photoconducting polymer nanocomposites with high electrophotographic sensitivity for both positive (Sλ+) and negative (Sλ−) signs of corona charging (up to 400 m2/J in 300-620 nm range) and high charge carrier photogeneration quantum yield (β up to 0.6) are developed on the base of p-conducting (Sλ+ ≫ Sλ−) polymer matrices (polyimides (PI), carbazolylcontaining (CzCP) polymers) and n-conducting low molecular mass additive (perylenediimide derivative (PDID)) in aggregated form. For p-composites (PI doped with PDID at content CA up to 50% wt.) the efficient hole photogeneration in PDID absorption band is related to the observed electron transfer from PI donor chain fragments with low ionization potential (ID = 6.8 eV) to the excited PDID aggregates as acceptors (with affinity EA = 1.8-2.0 eV). Low Sλ− value for p-composites is likely due to potential barrier formation between PDID particles (aggregates and clusters) involved in electron transport network. For n-composites (Sλ− ≫ Sλ+) (CzCP doped also with PDID) high Sλ− and β values are explained by the efficient electron photogeneration via excited charge transfer complex (exciplex) between excited PDID molecule as acceptor and CzCP carbazolyl pendant as donor (with ID = 7.4 eV) as well as electron transport network formation involving PDID particles. As it is only ionization potentials of polymer donor fragments that differ essentially for p- and n-composite, the conclusion is made that charge transfer donor-acceptor interaction in the ground state may be responsible for potential barrier formation between acceptor particles embedded in donor matrix. It is found that films of bipolar sensitive composites (Sλ+ ≈ Sλ−) (obtained by mixing p- and n-composites in solution) which have microsegregated structure are characterized by the highest Sλ+, Sλ− and β values. The photovoltaic effect is investigated for sandwich cells with (Al, ITO) electrodes. The best parameters are found for bipolar composite films (0.5-1.0 μm thick).