Semiconductor Halogenation in Molecular Highly-Oriented Layered p–n (n–p) Junctions

Organic p–n junctions attract widespread interest in the field of molecular electronics because of their unique optoelectronic singularities. Importantly, the molecular donor/acceptor character is strongly correlated to the degree of substitution, e.g., the introduction of electron-withdrawing groups. Herein, by gradually increasing the degree of peripheral fluorination on planar, D4h−symmetric iron(II) phthalocyanato (FePc) complexes, the energy level alignment and molecular order is defined in a metal-supported bilayered Pc-based junction using photoemission orbital tomography. This non-destructive method selectively allows identifying molecular levels of the hetero-architectures. It demonstrates that, while the symmetric fluorination of FePc does not disrupt the long-range order and degree of metal-to-molecule charge transfer in the first molecular layer, it strongly impacts the energy alignment in both the interface and topmost layer in the bilayered structures. The p–n junction formed in the bilayer of perhydrogenated FePc and perfluorinated FeF16Pc may serve as an ideal model for understanding the basic charge-transport phenomena at the metal-supported organic–organic interfaces, with possible application in photovoltaic devices.