Theoretical Study on the Rational Design of Cyano-Substituted P3HT Materials for OSCs: Substitution Effect on the Improvement of Photovoltaic Performance

Calculations have been made regarding the strong electron-withdrawing cyano (-CN) group, which was introduced onto the backbone of poly(3-hexylthiophene) (P3HT), as an effective way to improve the parameters essential for the photovoltaic performance of organic solar cells (OSCs). The substitution effect on the optical and photovoltaic properties of various CN-substituted P3HT are comprehensively investigated by means of density functional theory and molecular dynamics simulation. The results of theoretical modeling indicate that the direct introduction of strong electron-withdrawing group -CN onto the backbone of P3HT, can not only significantly reduce the HOMO level of polymer which leads to increased open circuit voltage (V-OC) in solar cells, but also exhibit red-shifted absorption spectra and increased hole mobility, which might lead to the enhancement of the short circuit current (J(SC)) and the fill factor (FF) in comparison to pristine P3HT and fluorine (F)-substituted P3HT. These results provide a fundamental understanding of how different electron-withdrawing groups influence the photophysical, electrochemical, and optoelectronic properties of conjugated polymers and potentially provide useful information for better design strategy for OSCs.