Density Functional Theory Study of Selenium-Substituted Low-Bandgap Donor-Acceptor-Donor Polymer

This is the author accepted manuscript. The final version is available from American Chemical Society via the DOI in this recordTheoretical study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor-acceptor-donor (D-A-D), 2,1,3-benzosele-nadiazole (A) as acceptor and 3,4-ethylenedioxyselenophene (D) as donor fragments, with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone has been found to be responsible for tuning the band gap, optical gap, open circuit (VOC), and short-circuit current density (JSC) in the polymers solar cells. D-A-D has a key role in charge separation and molecular architecture which ultimately influences the charge transport. Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. The polaron and bipolaron effects are also investigated which has a direct relation with visible light photocurrent generation. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D resulted in red-shifting of its onset of absorption. The simulated band gap of the D-A-D has excellent correlation with experimentally reported values for closely related systems, which validates the level of theory used. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives a theoretical VOC of about 1.02 eV. (Graph Presented)