Recently, we reported on the development of a new thin-film organic solar cell with an AM1 sunlight efficiency of about 0.7% for large area devices (∼1 cm2). This relatively high-efficiency MIS-Schottky barrier-type cell was based on merocyanine type photosensitizing dyes. In this paper we present additional experimental results and develop a comprehensive theoretical model to explain the observed photovoltaic properties. The model incorporates the generation, transport, and surface dissociation of excitons and field-dependent quantum efficiency. The low fill factor of 0.3 was attributed mainly to the field dependence of quantum efficiency. An exciton diffusion length of 60 Å was determined by analyzing the short-circuit photocurrent action spectra using the theoretical model developed. The diffusion potentials for metal/merocyanine Schottky barrier cells for six different metals were determined by C-V measurements; the diffusion potential increases with decreasing work function. As solar cells, these devices have higher efficiencies when there is a very thin interfacial oxide layer between the barrier forming metal and merocyanine.