Electrostatic Design of 3D Covalent Organic Networks

Abstract

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.

The Impact of Dipolar Layers on the Electronic Properties of Organic/Inorganic Hybrid Interfaces

“…Employing electrostatic design in covalent organic or metal-organic frameworks with properly arranged dipolar linkers can also be used to create quantumcheckerboards with electrostatic potential distributions localizing electrons and holes in spatially separated regions consisting of identical semiconducting entities. [287] Interestingly, such electrostatically tuned covalent networks have in the meantime also been realized in practice, albeit not in the bulk, but on surfaces. [288]…”

Electrostatic Design of Polar Metal–Organic Framework Thin Films

“…[41] From a practical point of view, one could envision to apply the energy staircase of the electronic levels in Figure 1c to guide the flow of charge carriers, to separate electrons and holes, or to dissociate excitons. [31] In that sense, the energetic staircase is somewhat reminiscent of the band diagram of a pin-junction typically used in photodetectors and solar cells. [42] There the linear position dependence of the band edges is not related to collective electrostatic effects.…”

“…It relies on the fabrication of structures containing periodic arrangements of polar entities. [30,31] The superposition of the fields of the periodically arranged dipoles result in so-called collective (also termed cooperative) electrostatic effects, which are commonly observed at organic-inorganic hybrid interfaces. [32][33][34][35][36] They originate from the fact that extended 2D layer of dipoles rigidly shift the electrostatic energy of electrons between the regions above and below the layers with the magnitude of the effect being proportional to the dipole density.…”

Ultrathin porphyrin and tetra-indole covalent organic frameworks for organic electronics applications

“…DFT calculations have been successfully employed toward the determination of electronic and optical properties of monolayer COFs in general [26][27][28][29][30][31][32][33] and in particular for porphyrin-and phthalocyanine-based COFs. [34][35][36][37][38] Moreover, simulation work in the literature has focused on the examination of in-plane CT mechanisms, either by means of the Boltzmann Transport Equation (BTE) theory [39][40][41] or by utilizing mixed quantum-classical dynamics methods. 41 Furthermore, the special case of planar molecules fused via non-articulated linkers, practically resulting in monolayer holey structures with…”