Theoretical exploration of optoelectronic performance of PM6:Y6 series-based organic solar cells

Organic solar cells (OSCs) have become a research focus due to their broad applications. In this work, the UV-Vis absorption spectra of the acceptor Y6, N3 and N4 as well as the donor PM6 were investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). It shows that the five functionals of B3LYP, PBE0, HSE06, the tuned CAM-B3LYP and the tuned ωB97XD can more accurately predict the UV-Vis absorption spectra of these molecules. The hole-electron analysis and Interfragment Charge Transfer method (IFCF) are used to study the electron transition mechanisms of the two types of systems, respectively. It indicated that the electron transition of Y6 and its derivatives is π-π* charge transfer excitation and local excitation on the aromatic backbone and the PM6 is mainly the π-π* excitation on the conjugated chain. Moreover, it was found that the HOMO and LUMO energy levels of the acceptor and donor molecules match. This study obtains some insights into the formation mechanism of UV-Vis absorption spectra, which provides a theoretical approach for the prediction and design of organic photovoltaic materials.