Abstract:
Self‐assembly of fullerene derivatives plays an important role in controlling photovoltaic performance of organic solar cells (OSCs). Herein, we have synthesized two covalently bonded phenyl substituted fullerene derivatives ‐N‐Mtheyl‐2‐[2,5‐bis(trifluoromethyl)phenyl] fullerenopyrrolidine (1) and N‐Methyl‐2‐[2,4bis(trifluoro‐methyl‐6‐methoxy)phenyl]fullerenopyrrolidine (2), which are employed as electron acceptors in OSCs. The self‐assembly of two aforementioned molecules were investigated in the binary solvent system of chloroform and methanol (1:1 volume ratio). Further, optical, electro‐chemical and micro‐structural properties of self assembled structures were also studied. It is found that the architecture of assembly is directed by the functional groupsatthe phenyl ring and solvent molecule. The molecule 1 possessing ‐CF3 group and the molecule 2 possessing additional ‐OMe group on fullerene unitform flowers and flakes like structures, respectively. The assembly structure of 1 gets converted from flower to disc like structure with the variation of solvent from methanol to hexane. The OSCs fabricated using molecule 1 and molecule 2 as acceptor with PTB7 donor showed a power conversion efficiency of 6.8 and 3.6%, respectively with high open circuit voltages of ∼0.8 V.
