Fundamental Study on Organic Solar Cells Based on Soluble Zinc Phthalocyanine

We investigated the potential of trifluoroethoxy-coated phthalocyanine [(4TFEO)4-ZnPc] as an organic thin-film solar cell material. (4TFEO)4-ZnPc dissolves well in several organic solvents, thus a fluorinated phthalocyanine (Pc) thin film can be fabricated by a wet process. Additionally, (4TFEO)4-ZnPc has lowest unoccupied molecular orbital (LUMO) energy level close to that of a fullerene derivative owing to the electron-withdrawing effect of fluorine substituents. We fabricated two types of fluorinated Pc solar cells by spin casting “(4TFEO)4-ZnPc single-layer solar cells” and “two-layer heterojunction solar cells” consisting of a (4TFEO)4-ZnPc layer and a poly(3-hexylthiophene) (P3HT) layer. P3HT is a common donor solar cell material. On the other hand, we used (4TFEO)4-ZnPc as an acceptor material. For the single-layer solar cells, the (4TFEO)4-ZnPc film acts as the photoactive layer of the solar cells, and P3HT/(4TFEO)4-ZnPc solar cell properties were improved as compared with that of P3HT or (4TFEO)4-ZnPc single-layer solar cells. Additionally, the photovoltaic properties of these solar cells were significantly improved by annealing treatment.