Charge-transfer excited states in the donor/acceptor interface from large-scale GW calculations

• DOI: 10.1063/1.5113944
• Publication Date: 2019-09-18T17:41:16Z
• Authors: Takatoshi Fujita; Yoshifumi Noguchi; Takeo Hoshi
• Keywords: 0103 physical sciences; 01 natural sciences; 7. Clean energy

Predicting the charge-transfer (CT) excited states across the donor/acceptor (D/A) interface is essential for understanding the charge photogeneration process in an organic solar cell. Here, we present a fragment-based GW implementation that can be applied to a D/A interface structure and thus enables accurate determination of the CT states. The implementation is based on the fragmentation approximation of the polarization function and the combined GW and Coulomb-hole plus screened exchange approximations for self-energies. The fragment-based GW is demonstrated by application to the pentacene/C60 interface structure containing more than 2000 atoms. The CT excitation energies were estimated from the quasiparticle energies and electron–hole screened Coulomb interactions; the computed energies are in reasonable agreement with experimental estimates from the external quantum efficiency measurements. We highlight the impact of the induced polarization effects on the electron–hole energetics. The proposed fragment-based GW method offers a first-principles tool to compute the quasiparticle energies and electronic excitation energies of organic materials.