An ab initio method on large sized molecular aggregate system: Predicting absorption spectra of crystalline organic semiconducting films

Theoretical description of electronically excited states of molecular aggregates at an ab initio level is computationally demanding. To reduce the computational cost, we propose a model Hamiltonian approach that approximates the electronically excited state wavefunction of the molecular aggregate. We benchmark our approach on a thiophene hexamer, as well as calculate the absorption spectra of several crystalline non-fullerene acceptors, including Y6 and ITIC, which are known for their high power conversion efficiency in organic solar cells. The method qualitatively predicts the experimentally measured spectral shape, which can be further linked to the molecular arrangement in the unit cell.(c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

A model Hamiltonian approach is proposed in this study to approximate the wavefunction of electronically excited states in molecular aggregates, reducing computational costs. The approach is tested on a thiophene hexamer and used to calculate the absorption spectra of crystalline non-fullerene acceptors, including Y6 and ITIC. The method provides a qualitative prediction of the experimentally measured spectral shape and its correlation with molecular arrangement in the unit cell.