Separate-path electron and hole transport across pi-stacked ferroelectrics for photovoltaic applications

Abstract

Electron and hole separate-path transport is theoretically found in the pi-stacked organic layers and columns. This effect might be a solution for the charge recombination problem. The building molecules, named 1,3,5-tricyano-2,4,6-tricarboxy-benzene, contain the mesogenic flat aromatic part and the terminal dipole groups which make the system ferroelectric. The diffusion path of the electrons cuts through the aromatic rings, while holes hop between the dipole groups. The transmission function and the charge mobilities, especially for the holes, are very sensitive to the distance between the molecular rings, due to the overlap of the pi-type orbitals. We verified that the separation of the diffusion paths is not destroyed by the application of the graphene leads. These features make the system suitable for the efficient solar cells, with the carrier mobilities higher than these in the organometal halide perovskites.