Bulk Heterojunction Solar Cells Based on P3HT: Modified PCBM Blend

The most promising structure for organic solar cells is a bulk heterojunction of a p-type donor and an n-type acceptor. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) are the most widely used donor and acceptor materials, respectively, in polymer solar cells (PSCs). However, the low LUMO (lowest unoccupied molecular orbital) energy level of PCBM limits the open circuit voltage (V_oc) of the organic solar cells based on P3HT. To increase Voc, two modified forms of PCBM, A and F have been previously synthesized and used as an electron acceptor. These are more soluble than PCBM in common organic solvents due to the increase of the organic moiety. The thin films of these show stronger absorption than PCBM in the range of 400–900 nm. The LUMO energy level of A and F are 0.15 eV and 0.25 eV higher than that of PCBM, respectively. The P3HT: A and P3HT: F show higher power conversion efficiency (PCE) of 3.88% and 4.23% respectively, while the PSC based on P3HT: PCBM shows a PCE of about 2.93% under the same conditions. The results indicate that the modified forms of PCBM, i.e., A and F, are excellent acceptors for PSCs based on bulk heterojunction active layers.