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Methanofullerenes, such as [6,6]-phenyl-C61-butyric acid methyl ester {[6,6]PC61BM (1a)}, were synthesized in good yields from the corresponding tosylhydrazones in an aqueous two-phase (o-dichlorobenzene-H2O) system under photoirradiation conditions. This simple and convenient procedure was adopted for the synthesis of thienyl analogues of PC61BM and its C70 analogue, PC71BM. [ABSTRACT FROM AUTHOR]

Methanofullerenes bearing both an ethyleneoxy side chain, −(CH 2 CH 2 O) n -, n = 1 or 2, and a 5-ethyl-2-thienyl group were prepared. These methanofullerenes were much more polar than PCBM and C 60 , and solubility in chlorobenzene (23–24 g/L) was comparable to that of PCBM. Planar heterojunction photovoltaic cells employing the methanofullerenes as an electron acceptor and copper phthalocyanine (CuPc) as an electron donor were fabricated. The short-circuit current density of the photovoltaic cell (4.61–4.66 mA/cm 2 ) was larger than that of the photovoltaic cell prepared from the standard fullerene acceptor, PCBM, (4.08 mA/cm 2 ), and consequently the power conversion efficiency was improved. Comparisons of contact angles of water and hexadecane on fullerene films indicated that the fullerenes with an ethyleneoxy side chain formed more stable interface with CuPc than PCBM. These results suggest that side chain engineering aiming at stable p - n interface is an attractive strategy for designing efficient organic photovoltaic cells. [ABSTRACT FROM AUTHOR]

A series of arylated dihydrofullerene derivatives were synthesized to elucidate the effective design of fullerene derivatives for enhancing the performance of organic photovoltaics. The LUMO energy of the fullerenes was estimated by the first reduction potential and theoretical calculations. The results showed that the methoxy groups substituted at spatial proximity to the fullerene core offered significant stabilization of the LUMO level. The stabilizing effect of the directly arylated fullerenes is more significant than that of conventional methanofullerenes. The theoretical investigation was performed with regard to the electronic interaction between the methoxy and fullerene moieties. [ABSTRACT FROM AUTHOR]

Abstract: Novel methanofullerenes 3 having ethylthienyl and/or n-pentyl groups were designed and synthesized for the purpose of developing new acceptors for an organic photovoltaic cell with higher performance than that of the [6,6]-phenyl-C61-butylic acid methyl ester (PCBM) used as the standard acceptor. The electronic absorption spectra and cyclic voltammetry (CV) of 3, PCBM, and [6,6]-(thiophene-2-yl)-C61-butylic acid methyl ester (ThCBM) were measured to estimate solubility and reduction potentials as characteristics of n-type semiconductor for organic photovoltaic devices. The CV measurements revealed reversible reduction waves for all of the methanofullerenes and the first reduction potentials of the n-pentyl-substituted 1-(5-ethylthiophene-2-yl)-[6,6]-methanofullerene[60] (3b) and 1-phenyl-[6,6]-methanofullerene[60] (3c) were negatively shifted compared to those of the corresponding terminal methyl ester-substituted homologues (3a and PCBM). The performances of photovoltaic devices consisting of 3b and 3c were slightly higher than those of PCBM. [ABSTRACT FROM AUTHOR]