Charge transfer at n-doped organic-organic heterojunctions

The impact of n -doping on the electronic structure of two organic-organic heterojunctions (OOH) is investigated with ultraviolet photoemission spectroscopy. The two OOHs have a type II staggered gap configuration corresponding to donor-acceptor pairs applicable to photovoltaic cells. Both molecular top acceptor layers have large electron affinity, which leads to electron transfer from the donor layer. The result is a significant interface dipole (Δ∼0.4-0.6 eV) between the two molecular films, at both undoped and doped interfaces, consistent with a stronger interaction between molecular constituents than in wide, largely overlapping, band gap OOHs.