Molecular design of the NDI derivatives electron acceptors and theoretical adjustment of the open-circuit voltage

Abstract

Based on naphthalene diimide (NDI) unit, 6 electron acceptor molecules An (n=1−6) have been designed, and their geometric configurations, the characteristics of frontier molecular orbital and optical properties have been investigated by density functional theory. Furthermore, the donor-acceptor (D-A) interfaces are respectively simulated by combining the 6 acceptors with the selected three donors Dm (m=1−3). Then the degree of interface recombination is evaluated from the single molecule scale. The results provide an efficient way to adjust the recombination that is through strong H-bond interaction to change the distance and displacements of D-A interface by introducing N, O, S heteroatoms. The fine-tuning of D-A interfacial stacking, reducing interface recombination, can enhance the open-circuit voltage (V oc). In addition, the proper calculated results of electronic coupling between HOMO of donors and LUMO of acceptors showing the donor and acceptor materials both with good planar combined can lead to serious recombination against high open-circuit voltage. While in organic solar cell, acceptor with good planar combined with non-planar donor materials, to form optical active layer, is an effective approach to obtain high V oc. Considering ΔE L , V if , the planarity of donor and acceptor molecules and light absorption efficiency, D3-A5 combination is the most promising candidate of optical active layer materials in organic solar cell.