Ferroelectric $π$-stacks of molecules with the energy gaps in the sunlight range
Ferroelectric $π$-stacked molecular wires for solar cell applications are theoretically designed, in such a way that their energy gaps fall within visible and infrared range of the Sun radiation. Band engineering is tailored by a modification of the number of the aromatic rings and via a choice of the number and kind of the dipole groups. The electronic structures of molecular wires and the chemical character of the electron-hole pair are analyzed within the density functional theory (DFT) framework and the hybrid DFT approach by means of the B3LYP scheme. Moreover, it is found that one of the advantageous properties of these systems - namely the separate-path electron and hole transport - reported earlier, still holds for the larger molecules, due to the dipole selection rules for the electron-hole generation, which do not allow the lowest optical transitions between the states localized at the same part of the molecule.