A study on efficiency enhancement in solution processed small-molecule based organic solar cells (OSCs) utilizing various phthalocyanine-tetrabenzoporphyrin hybrid macrocycles is reported. By replacement of aza links at meso position by methine groups, the optical absorption at B band of porphyrinoid complexes is improved, the energy bandgap is enlarged, and stacking of the discotic molecules is probably changed from pseudohexagonal structures to 2-D rectangular lattices. Results from molecular orbital (MO) calculation by using B3LYPoptimized geometries calculated with 6-31G(d) indicate that the intensification of optical absorption and the modification of electronic band structure is mainly due to the difference of MO coefficients at meso positions, resulting in a marked lifting of the degeneracy of the MOs derived from highest occupied molecular orbitals and/or lowest unoccupied molecular orbitals. By controlling the numbers of aza links at meso position, active layer thickness and nanoscale phase separation, the external quantum efficiency at B band and power conversion efficiency of OSCs utilizing phthalocyanine-tetrabenzoporphyrin hybrid macrocycles is improved to 53% and 5.3%, respectively.

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