This paper describes the preparation of fluorinated graphene nanosheets (FGNs) through photoexfoliation of fluorinated graphite (FG) in the liquid phase. We discovered that UV irradiation of FG dispersions in N-methyl-2-pyrolidone facilitated exfoliation to give FGNs. Transmission electron microscopy and atomic force microscopy revealed that the average thickness of the FGNs was approximately 3 nm; they were considerably thinner than the nanosheets prepared using a conventional sonication approach. Furthermore, when the FGNs were deposited uniformly onto substrates (through spin coating), they formed effective cathode interlayers for polymer solar cells (PSCs), the efficiency of which was 60% greater than that of PSCs containing FGNs prepared through ultrasonication.