Small molecule organic solar cells based on copper phthalocyanine (CuPc) and fullerene were fabricated using C-60 and C-70 as acceptors, respectively. The results showed that photovoltaic performances of the cells using C-70-acceptor were better than that of C-60-acceptor. The mechanisms of enhancement were systemically discussed on the energy level difference of the heterojunction, light absorption of the materials and quantum current distribution in the two kinds of fullerene molecules. The degradation of these two kinds of cells exposed in the air without encapsulation was also studied. It was found that the cells using C-70 as an acceptor showed a better stability. This is because C-60 can be easily destroyed by oxygen than C-70. Thus, using C-70 as an acceptor not only can increase the photovoltaic characteristics, but it also can dramatically improve the stability of the cells. (C) 2010 Elsevier B.V. All rights reserved.