An innovative strategy for electrostatically designing the electronic structure of 3D bulk materials is proposed to control charge carriers at the nanoscale. This is achieved by shifting the electronic levels of chemically identical semiconducting elements through the periodic arrangement of polar functional groups. For the example of covalent organic networks, by first-principles calculations, the resulting collective electrostatic effects are shown to allow a targeted manipulation of the electronic landscape such that spatially confined pathways for electrons and holes can be realized. Mimicking donor-acceptor bulk heterojunctions, the new materials hold high promise for photovoltaic applications. The distinct advantage over the conventional approach of splitting excitons through chemically distinct donor and acceptor units is that here the magnitude of the band offset can be continuously tuned by varying the dipole density. A particularly promising feature of the suggested strategy is its structural versatility, which also enables the realization of more complex quantum structures such as quantum-cascades and quantum-checkerboards.
Keywords: covalent organic frameworks; density functional theory; electrostatic design; solar cells.
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