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

Abstract

Photoconducting polymer nanocomposites with high electrophotographic sensitivity for both positive (S λ +) and negative (S λ −) signs of corona charging (up to 400 m 2/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 (S λ + ≫ S λ −) 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 C A 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 (I D = 6.8 eV) to the excited PDID aggregates as acceptors (with affinity E A = 1.8–2.0 eV). Low S λ − 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 (S λ − ≫ S λ +) (CzCP doped also with PDID) high S λ − 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 I D = 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 (S λ + ≈ S λ −) (obtained by mixing p- and n-composites in solution) which have microsegregated structure are characterized by the highest S λ +, S λ − 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).