Accurate Description of the Electronic Structure of Organic Semiconductors by GW Methods

Organic photovoltaics are attractive for large area, low cost applications and for flexible, lightweight modules. However, their relatively low efficiency leaves much to be desired. Insight from computation may help improve device performance by designing new organic semiconductors and ordered nanostructured interfaces. It is important to obtain an accurate description of the electronic structure of organic semiconductors, including the fundamental gaps and absolute positions of the donor HOMO and the acceptor LUMO at the interface. This requires going beyond ground state density functional theory (DFT).

Many-body perturbation theory is often used for this purpose within the GW approximation, where G is the one particle Green function and W is the dynamically screened Coulomb interaction. Typically, GW calculations are performed as a non-self-consistent perturbative correction to DFT eigenvalues, known as G₀W₀. The predictive power of G₀W₀ is limited by a strong dependence of the results on the DFT starting point. Self-interaction errors (SIE), spurious charge transfer, and incorrect ordering and hybridization of molecular orbitals may propagate from the DFT level to G₀W₀. These issues may be addressed by judiciously choosing a hybrid DFT starting point or by going beyond G₀W₀ to a higher level of self-consistency. Here, this is demonstrated for prototypical organic semiconductors and interfaces.

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