Charge carriers at the interfaces in organic heterojunctions and superlawices: polarization barriers

Summary form only given. At the interfaces of organic heterojunctions between two undoped organic semiconductors the polarization double barrier (PDB) is shown to appear due to difference in polarization energies P of charge carriers in each layer. Such PDB corresponds to attraction of both electrons and holes to the interface in the molecular layer B (with low P/sup B/) and repulsion of both carriers the interface in the layer A (with high P/sup A/). PDB is quite different from p/n junction in doped semiconductors due to its symmetric effect on charge carriers, independently of their sing. Depending on properties of single molecules in each molecular layer, PDB can lead to selective charge injection from one layer to another or charge confinement at the interfaces and may influence significantly photophysical and optical properties of organic heterojunctions. Estimates of the PDB parameters for existing organic molecules are presented, using simple theory of charge-dipole interactions and image forces at the interfaces. Sizable FIDB of 0.2-0.4 eV is predicted at the interface of heterojunctions formed between e.g. rubrene and p-iodanil or Cu-phthalocyanine and pyromelific anhydride(PMDA).