Effects of modifications of the heteroatoms on fine‐tuning the photophysical proprieties of A‐π‐D‐π‐A small molecules for photovoltaic applications

Abstract

An effective way to enhance the photovoltaic properties of a small molecule is to modify the side groups into donor units. Herein three news small molecules A‐π‐D‐π‐A, denoted Dye1‐3, have been designed, from experimentally reported one noted (R), by insertion of various heteroatoms (S, O, Se) on the electron‐donating benzodithiophene (Donor (D = BDT)) part. From the calculated results, the dihedral angle between BDT and side‐chain affects the distribution of density on the ground state, gap energy, and intramolecular charge transfer of Dyes. In particular, the Dye3 compound, with the smaller dihedral angle, shows that the furan groups in the side chain of D, participates in the distribution of density on the ground state and consequently the charge transfer is improved. Additionally, Dye3 has the lower reorganization energy revealing that this material exhibits better charge mobility. Using the Scharber diagram, Dye3‐PCBM heterojunction shows a power conversion efficiency of around 7%. Overall, this work suggests that the photovoltaic properties can be affected by the modification of heteroatoms on side groups of donor parts in small molecules.