Fluorination effects of A-D-A-type small molecules on physical property and the performance of organic solar cell

Abstract Four new molecules with acceptor-donor-acceptor (A-D-A) configuration where cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) as the electron-donating core connecting to cyano(CN)-substituted 2,1,3-benzothiaidiazole (BT) as electron-withdrawing end groups are reported. With the same acceptor CN-BT, we found that CPDT can serve as a better donor as compared to that of dithieno[3, 2-b: 2′, 3′-d]silole (DTS) to give stronger intramolecular charge transfer (ICT) character and therefore better light harvesting ability. The number and orientation of F-substitution on the BT ring, giving a clear structure-property relationship, can subtly manipulate the physical characteristics. These A-D-A type molecules were employed as electron donor in conjunction with C 70 as the electron acceptor in vacuum-deposited bulk heterojunction (BHJ) small-molecule organic solar cells (SMOSCs). Among them, the device based on CBCIF containing BT ring with one F group directing toward the CPDT core gave the best device performance with a power conversion efficiency of 4.94% with J sc of 10.16 mAcm −2 , V oc of 0.98 V, fill factor (FF) of 0.50. The superior device characteristics were attributed to the suitable morphology of the donor/C 70 film.