Efficient Solution Processable Polymer Solar Cells Using Newly Designed and Synthesized Fullerene Derivatives

Two modified PC 60 BM and PC 70 BM fullerene derivates denoted as C 60 DAM and C 70 DAM, respectively, were synthesized and characterized. Through the structural modification, the lowest unoccupied molecular orbital (LUMO) energy level of these fullerene derivatives can be raised as much as 0.15 eV with respect to that of their parent fullerene derivatives, which is possibly ascribed to the electron-donating nature of their substituted moiety. Bulk heterojunction (BHJ) polymer solar cells (PSCs) fabricated with poly(3-hexylthiophene) (P3HT) as electron donor and either C 60 DAM or C 70 DAM as electron acceptor showed both higher open-circuit voltage ( V oc ) and short-circuit current ( J sc ), resulting in enhanced power conversion efficiency (PCE) (3.23% for P3HT: C 60 DAM and 4.45% for P3HT: C 70 DAM ) as compared to corresponding PC 60 BM. The enhanced J sc and higher V oc values have been ascribed to the stronger absorption in the visible region and increase in LUMO level of the modified fullerene derivatives compared to their pristine fullerene derivatives. The BHJ PSC with P3HT: C 70 DAM blend cast from high boiling point chloronaphthalene (CN), 1,8-diiodoctane (DIO), and 1,8-octanedithiol (OT) as additives showed PCE of 5.63%, 4.75%, and 4.95%, respectively. The additive-treated P3HT: C 70 DAM interpenetrating network of the blend and strong absorption may be the reasons for the enhancement of PCE.