Charge Transfer Screening and Energy Level Alignment at Complex Organic–Inorganic Interfaces: A Tractable Ab Initio GW Approach

The energy level alignment (ELA) at organic-inorganic interfaces quantifies charge injection barriers in organic and molecular electronic devices. Many-body perturbation theory in the GW approximation enables the quantitative prediction of ELA in many systems but can be computationally challenging for large interfaces. We have developed an approach [1] to perform GW calculations on large interfaces, which involves the eXpansion of the polarizability (chi) matrix from a unit cell to the supercell, the Addition of chi from the two subsystems, and the use of wavefunctions from the Full interface to compute the self-energies. This XAF-GW method has been shown to work even in the presence of interface hybridization to form bonding and anti-bonding orbitals. Here, we modify the XAF-GW approach to specifically account for many-body interactions due to charge transfer effects and obtain excellent agreement with benchmark GW calculations with significantly reduced computational cost [2]. We show that many-body interactions lead to gate-tunable molecular HOMO-LUMO gaps in a F4TCNQ/graphene interface. By comparison with a two-dimensional electron gas model, we also show the importance of explicitly accounting for intraband transitions in determining the charge transfer screening in organic-inorganic interfaces.

[1] JCTC 15, 3824 (2019)

[2] JPCL 12, 8841 (2021)