Fullerene-Grafted Graphene for Efficient Bulk Heterojunction Polymer Photovoltaic Devices

A simple lithiation reaction was developed to covalently attach monosubstituted C60 onto graphene nanosheets. Detailed spectroscopic (e.g., Fourier transform infrared, Raman) analyses indicated that C60 molecules were covalently attached onto the graphene surface through monosubstitution. Transmission electron microscopic (TEM) observation revealed that these monosubstituted C60 moieties acted as nucleation centers to promote the formation of C60 aggregates of ∼5 nm in diameter on the graphene surface. The resultant C60-grafted graphene nanosheets were used as electron acceptors in poly(3-hexylthiophene)-based bulk heterojunction solar cells to significantly improve the electron transport, and hence the overall device performance, yielding a power conversion efficiency of ∼1.22%.