Advanced NMR Studies Of Fullerene Derivatives

In recent years, organic solar cell(OSC) devices containing fullerene derivatives have diverse applications due to their desirable power conversion efficiency(PCE), light weight,large-area processability and low cost. A series of fullerene derivatives such as the Diels-Alder derivatives of C60 with indene have been synthesized and proved to be the best electron-accepting n-type materials by far. With poly(3-hexylthiopene)(P3HT) as donor material, the PCE values of bulk heterojunction(BHJ) OSCs are 7.5% for Indene-C60bisadduct(IC60BA) and 5.9% for C60 bearing methylene and indene(C60(CH2)(Indene)).However, it should be noted that these C60 derivatives are often used as mixture of isomers when blending with donor materials in OSC devices. These isomers cause disorder in the molecular packing, which adversely influence the electron transporting properties.This is a big disadvantage for further improvement of the devices performance. Moreover,the large-scale production for mixtures of C60 derivatives isomers is likely to suffer from the problem with batch-to-batch reproducibility, since different isomers distributions can occur during synthesis. So it is necessary to study the isomers of bisadduct and address the issue.Multidimensional NMR has shown great promise for the analysis of the maximum number and detailed structures of isomers present in C60 derivatives. Using the combination of 1H-1H COSY, NOESY and 1H-13 C g HSQC 2D-NMR experiments, the maximum number and structures of the bisadduct isomers of C60 derivatives can be determined unambiguously. The tendency of chemical shift in 1H NMR has been used to determine the addition sites of isomers. With the aid of HPLC and UV-Vis spectroscopy,the isomers were separated and studied, comfirming the results of NMR, so that further isomers analysis and PCE improvements could be processed.