Cascade donor–acceptor organic ferroelectric layers, between graphene sheets, for solar cell applications

Abstract

Organic ferroelectric layers sandwiched between the graphene sheets are presented as a model of the solar cell. The investigated systems display many advantageous properties: 1) the cascade energy-levels alignment, 2) simultaneous donor and acceptor character depending on the chargecarrier direction, 3) the charge-transfer excitonic type, 4) the induced polarization of the electrodes, leading to a substantial work-function change of the anode and cathode -around ±1.5 eV, respectively.PACS numbers:

Ferroelectric $$\pi $$ π -stacks of molecules with the energy gaps in the sunlight range

“…There are a number of important implications of using the dipole groups: i) the hydrogen bonds via the COOH groups within the planes restrict the electronic transport and dissipation of energy in the directions perpendicular to the photovoltaic path, ii) the polarization generated across the solar device orders the energy levels in a cascade [6], iii) the electronic transport along the πstacks is restricted to the π-conjugated rings for the electrons, and holes move between the dipole groups [7], iv) an adsorption of the optically active molecules at the surfaces of the transparent conductive oxides, used as the electrodes, leads to the high power conversion when it is realized with the COOH group [28]. Therefore, it is usefull to examine various dipole groups for their impact on the energy gaps.…”

“…This is advantageous for the solar batteries, where the planar current would cause only a dissipation of an energy. Therefore, in the previous works [6,7], we studied the layers of molecules with the COOH terminal groups as the connecting parts for building the networks. The COOH group possesses also a small dipole moment.…”

“…The ferroelectrically ordered molecules, composed of benzene rings and two dipole groups (COOH and CH 2 CN), arranged in the π-type stacks of layers or the molecular wires, show many appealing effects [6,7]. In particular, the energy levels of the subsequent layers (or molecules in a stack) are aligned in a cascade, and this holds for the valence and conduction band as well [6][7][8]. Each layer is simultaneously a donor and acceptor of electrons and holes, depending on a direction of the carrier motion [6].…”

“…In particular, the energy levels of the subsequent layers (or molecules in a stack) are aligned in a cascade, and this holds for the valence and conduction band as well [6][7][8]. Each layer is simultaneously a donor and acceptor of electrons and holes, depending on a direction of the carrier motion [6]. The excitons in such layers are localized and have the charge-transfer character from the dipole group to the aromatic central ring.…”

“…The electric field generated by the ferroelectrically ordered dipole groups leads to a polarization which is induced at electrodes. This effect for the graphene sheets, chosen as the electrodes, causes a change of the work function by ±1.5 eV for the anode and cathode, respectively [6]. Moreover, the electrons and holes move across such π-stacks along different paths: the electrons through the central rings and holes between the dipole groups [7].…”