Fullerene-Grafted Graphene for Efficient Bulk Heterojunction Polymer Photovoltaic Devices

A simple lithiation reaction was developed to covalently attach monosubstituted C-60 onto graphene nanosheets. Detailed spectroscopic (e.g., Fourier transform infrared, Raman) analyses indicated that C-60 molecules were covalently attached onto the graphene surface through monosubstitution. Transmission electron microscopic (TEM) observation revealed that these monosubstituted C-60 moieties acted as nucleation centers to promote the formation of C-60 aggregates of similar to 5 nm in diameter on the graphene surface. The resultant C-60-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 similar to 1.22%.