Performance comparison of BHJ organic solar cells based on P3HT with PC70BM and ICBA

In this work we compare the performance of several bulk-heterojunction (BHJ) organic solar cells fabricated using poly(3-hexylthiophene) (P3HT) as electron donor material blended with two different fullerene derivatives for the active layer. We focus in the electron acceptor material, using two similar fullerenes to study their effects on the power conversion efficiency (PCE) of the solar cells. For this analysis the fullerenes 1´,1",4´,4"-tetrahydro-di[1,4]methanonaphthaleno[5,6]fullerene-C60 (ICBA) and [6,6]-Phenyl C71 butyric acid methyl ester (PC70BM) were used. The architecture was ITO (120 nm) / PEDOT:PSS (40 nm) / P3HT:Fullerene (~200 nm) / Ca (25 nm) / Ag (100 nm) for all the samples. In addition, we fabricated several samples replacing the Ca layer for a film of poly[(9,9-bis (3´-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl fluorene)] (PFN) as surface modifier with a thickness of 10 nm between the blend layer and metallic cathode. The PCE in samples fabricated with ICBA were lower than those for samples fabricated with PC70BM. In the other hand, PCE and fill factor (FF) in samples fabricated with Ca were higher than those for samples fabricated with PFN.