Effect of Halogen-terminated Additives on the Performance and the Nanostructure of All-polymer Solar Cells

Here, we report the influence of halogen-terminated additives on the performance and the nanostructure of all-polymer solar cells that are made with bulk heterojunction (BHJ) films of poly(3-hexylthiophene) (P3HT) (as an electron donor) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) (as an electron acceptor). Diiodooctane (DIO) and dibromooctane (DBO) were employed as additives in order to compare the effect of different halogen groups (bromine and iodine). Results showed that the power conversion efficiency of devices was slightly (∼15%) improved by using additives due to the increased open-circuit voltage and fill factor. The synchrotron radiation grazingincidence X-ray diffraction (GIXD) measurements disclosed that the performance improvement was closely related to the relatively well-evolved nanostructures in the P3HT:F8BT films caused by the additives.