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

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.

Automated summary

Through computational analysis and molecular dynamics simulations, the effect of chalcogen atoms on polymer solar cell materials was studied. It was found that sulfur and selenium-based polymers have higher density of states and closer molecular packing, thus having the potential for practical design of efficient polymer solar cells.