On the Structural and Optoelectronic Properties of Chemically Modified Oligothiophenes with Electron-Withdrawing Substituents for Organic Solar Cell Applications: A DFT/TDDFT Study

摘要

Solar cells based on conjugated polymers have been gaining attention in the recent decades due to its various potential advantages. In this study, several oligothiophene derivatives based on poly(3-hexylthiophene-2,5-diyl) (P3HT) were investigated by performing density functional and time-dependent density functional theory based calculations. The structural properties of various oligothiophenes substituted with electron-withdrawing groups (F, Cl, CN, NO2, COCH3) in its bithiophene monomer exhibited planar and non-planar structures. These structural properties depend on the interaction of the substituent and the surrounding molecules of the oligothiophenes. It is observed that the oligothiophenes with planar structures have decreased E-Gap while those with non-planar structures have increased E-Gap. Also, the effect of substitution on the frontier orbital energies was explored and it is observed that F, Cl, and CN-substituted derivatives decrease in E-LUMO more than E-HOMO resulting to smaller E-Gap. These changes in E-Gap are attributed to the induced structural and electronic changes in the oligothiophenes by the substituents. Furthermore, other properties (exciton binding energy, ionization potential, and open-circuit voltage) relevant to organic solar cells were investigated. It was found that cyano substituted P3HT is a good polymer blend candidate for organic solar cells. In general, this study shows how the optoelectronic properties of P3HT could be significantly improved via electron-withdrawing substitutions for solar cell applications.