Synthesis and properties of novel methanofullerenes having ethylthienyl and/or n-pentyl group for photovoltaic cells

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-C 61 -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)-C 61 -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.