Molecular level understanding of the chalcogen atom effect on chalcogen-based polymers through electrostatic potential, non-covalent interactions, excited state behaviour, and radial distribution function

Abstract

Polymer donor materials have been considered as a game changer, especially in the early history of polymer solar cells. However, much progress is the result of hard work resulting from hit and miss experiments. A deeper understanding of the electronic behavior of polymeric materials is necessary to select efficient materials for polymer solar cells. A detailed computational analysis is performed on the chalcogen-based polymers CP1, CP2, and CP3 to study the effect of chalcogen atoms on their non-covalent interactions, structural and electronic properties. The alteration of the chalcogen atoms significantly changed the electronic and excited behavior of the polymers. Moreover, the chalcogen atoms also exerted a significant effect on nearby groups. Selenium had more of a polarization effect on molecules compared with other chalcogen atoms. Polymer:Y6 complexes were also studied to determine rules for donor:acceptor pair selection. Significance changes were observed on changing the chalcogen atoms. The sulfur and selenium-based polymers CP2 and CP3 exhibited higher density of states near to the Fermi level in comparison with the oxygen-based polymer CP1. The effect of chalcogen atoms on molecular packing and blend morphology was studied using molecular dynamics simulations. The sulfur-based polymer showed closer packing compared with the other polymers in both pure and blended form. The selenium-based polymer CP3 showed lower free energy of mixing and Flory–Huggins parameter values for various solvents. Our detailed multi-dimensional modelling thus has the potential to assist in the practical design of chalcogen-based polymers for efficient polymer solar cells.