A comparative study on the performances of small molecule organic solar cells based on CuPc/C60 and CuPc/C70

Small molecule organic solar cells based on copper phthalocyanine (CuPc) and fullerene were fabricated using C60 and C70 as acceptors, respectively. The results showed that photovoltaic performances of the cells using C70-acceptor were better than that of C60-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 C70 as an acceptor showed a better stability. This is because C60 can be easily destroyed by oxygen than C70. Thus, using C70 as an acceptor not only can increase the photovoltaic characteristics, but it also can dramatically improve the stability of the cells.