Photoelectron Spectroscopy on Polycyclic Hydrocarbon–F₆TCNNQ Interfaces

The organic heterojunction between polycyclic hydrocarbons [pentacene, dibenzo[a,l]pentacene (DBP)] and hexafluorotetracyanonaphthoquinodimethane (F₆TCNNQ) was investigated by photoelectron spectroscopy. The heterojunction consisted of thin films prepared by a stepwise evaporation process. As a result, a charge-transfer interface is formed, where both polycyclic hydrocarbons acted as electron donors and F₆TCNNQ acted as an electron acceptor. This charge transfer was determined as a localized charge transfer with an ionic character because the F₆TCNNQ anion was observed in the characteristic nitrogen and carbon core levels and the valence-level data showed insulating/semiconducting behavior. The additional benzene rings in DBP lead to a stronger pronunciation of the F₆TCNNQ anion characteristics in the heterojunction compared to that in the pentacene heterojunction because of a different interface morphology.