Organic solar cells based on planar metallophthalocyanines (MPc, M = Cu, Zn, Pd, Pc)/3,4,9,10-perylene tetracarboxylic bisbenzimidazole (PTCBI) were investigated. PdPc/PTCBI solar cells have a peak external quantum efficiency of 30.9%, which is almost twice as those of conventional solar cells based on CuPc and ZnPc/PTCBI. Optical modeling was carried out using a transfer matrix algorithm in order to determine the exciton diffusion lengths for four MPcs. External quantum efficiency measurement and optical modeling indicate that PdPc has the longest exciton diffusion length among four different MPcs, leading to a power conversion efficiency of 1.3% and a short circuit current density of 4.0 mA/cm2 under the illumination of AM 1.5 G 100 mW/cm2. When fullerene (C60) was used as an acceptor, solar cells based on PdPc exhibit a short circuit current density of 6.8 mA/cm2, resulting in a power conversion efficiency of 2.2%, while solar cells based on CuPc show 1.6%.