This chapter presents expected applications of molecular layer deposition (MLD) and related thin-film organic photonic/electronic materials to solar energy conversion systems. It discusses applications to photosynthesis devices. Dye-sensitized photovoltaic devices have attracted much attention as cost-effective solar energy conversion modules. In waveguide-type photovoltaic devices, the optical coupling method for introducing light beams into the optical waveguides of the photovoltaic device is an important issue. The chapter presents concepts of film-based integrated solar energy conversion systems and related devices such as the integrated photonic/electronic/chemical system and light beam collecting films. Thin-film photovoltaic devices or photosynthesis devices containing semiconductor flakes are embedded in the film. The sensitization with the p/n-stacked structure reported has a distinct advantage in that it will be able to extend toward multistacked structures consisting of molecules of more than three kinds because the structures might be fabricated by MLD utilizing electrostatic force.