Effective Fermi-Level Modulation of Two-Dimensional Conjugated Covalent Organic Frameworks Achieved by Introducing p-Type Organic Dopants

Abstract

Covalent organic frameworks (COFs) are a new emerging class of two-dimensional functional materials, and their unique electronic character plays a key role in practical applications. Here, to provide a useful strategy to tune the electronic character of COFs, doping effects with organic molecular acceptors, TCNQ, F4TCNQ, and TCNE, on the frontier orbital energy levels of sp2c-COF and COF366 mono- and bilayers are explored. Due to the charge transfer from COFs to dopants, the Fermi level is shifted to a lower energy and drops into the top valence band of sp2c-COF and COF366, and the VBM/CBM energy level of COFs is also decreased. Moreover, the increased electron density shifts the LUMO energy level of dopants to a higher energy. Then, two electronic states, the top valence band of COFs and the LUMO of the p-type dopants, are pinned around the Fermi level. It means that the organic molecular acceptor serves as an effective p-type dopant for COFs. In addition, it is confirmed that the stronger the electron-accepting ability of p-type dopants or the higher the surface density of the dopants, the larger the variation of the frontier energy levels of COF monolayers will be. Thereby, an overall linear correlation between the electronic property variations of COFs and the charge transfer amount from COFs to p-type dopants is observed. Our results proved that surface doping with organic molecular acceptors is a reliable approach to modulate the frontier energy level of COFs, which provides an effective strategy to optimize the performance of COF-based devices.

Melt-Processable and Thermally Driven Self-Healing Luminescent Cu(I) Hybrid Metal Halides

“…32 However, it is generally accepted that the relative laws and trends are reliable under the same calculation method. 33,34 Considering electron transition energies are mainly dominated by the frontier energy bands, density of states projected (PDOS) onto different atom types involved in C 12 H 28 NCuCl 2 and C 20 H 48 N 2 Cu 4 Cl 6 were analyzed and shown in Figures 3g and 3h. Further frontier energy band diagram was constructed based on the PDOS and BS results to illustrate their luminescence mechanism, as presented in Figures 3i and 3j.…”

“…It is because the high-frequency exchange function is not introduced in the standard DFT-PBE level, which is likely to underestimate absolute VBM–CBM energy gaps . However, it is generally accepted that the relative laws and trends are reliable under the same calculation method. , …”

n-Type doping of BiVO4 with different F-doped concentrations for improving the electronic character of BiVO4 as a photoanode nanomaterial for solar water splitting: a first-principles study

“…Considering the standard DFT-PBE level tends to underestimate absolute VBM-CBM energy gaps, the electronic structures of pristine BiVO 4 and F-doped BiVO 4 were calculated by more accurate range-separated Heyd–Scuseria–Ernzerhof (HSE) hybridization functions, 43,44 for which the screening parameter was set to 0.2 Å −1 and the Hartree–Fock mixing parameter was set to α = 0.15. Considering it is generally accepted that the relative laws and trends, such as relative energy level shifts, are reliable under the same calculation method, 45 the energy level of alignment of pristine BiVO 4 and F-doped BiVO 4 was also examined by PBE functional for comparison.…”

How spin state and oxidation number of transition metal atoms determine molecular adsorption: a first-principles case study for NH3

“…Surface modification is an effective one, since it can affect molecular adsorption and catalytic behavior through introducing impurity levels near the Fermi energy. 8–10 For example, Fan et al reported that the d-orbital of doped transition metal (TM) atoms plays an important role in activating MoS 2 to adsorb gas molecules. 11 Similarly, non-metals can also induce gap states as reported by Yang et al For example, they confirmed that N–In 2 O 3 generates a mid-gap energy state, reduces the band gap of the photocatalyst, and improves solar energy utilization, which has a highly selectivity of CO 2 reduction to methanol.…”