Molecular Design Of Naphthalene Diimide And Benzothiadiazole Electron Acceptor Materials And Theoretical Regulation Of Open Circuit Voltage

In this dissertation, we designed a series of non-fullerenes electron acceptor molecules with A'-?-A-?-A' structure. We also simulated the Donor-Acceptor(D-A) interface and evaluated the degree of interface recombination from the single molecule scale. We hope this will provide theoretical supports in designing and synthsizing new materials for high-performance organic solar cells. The work mainly includes two parts as follows:1. Based on naphthalene diimide (NDI) unit,6 electron acceptor molecules An (n= 1 to 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 D-A interface are respectively simulated by combining the 6 acceptors with the selected three donors Dm (m= 1 to 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 (Voc). 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 Voc Considering ?EL, Vif,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.2. Based on benzothiadiazole unit, a series of electron acceptor molecules with A'?-A-?-A' structure have been designed, and their geometric configurations, the characteristics of frontier molecular orbital, optical properties and electronic reorganization energy have been investigated by density functional theory. And it has been studied the solvation effect of molecular properties. Furthermore, the D-A interface are respectively simulated by combining the excellent acceptors with the selected two donors. Then the degree of interface recombination is evaluated by means of electronic coupling (Vif) calculating between HOMO of donors and LUMO of acceptors.The results show that different ?-bridge can change the energy gap through regulating HOMO energy levels. For adjust LUMO energy levels and the energy gap at the same time, the most effective way is to modify benzothiadiazole with a reasonable substituent. The results proved once more that acceptor with good planar combined with non-planar donor materials, to form optical active layer in organic solar cell, should be a promising approach for preventing interface recombination and achieving high open-circuit voltage (Voc). Considering ?EL, Vif, Voc, light absorption efficiency, solvation effect and so on, D1-1a? and D1-2a? combination is the most promising candidate of optical active layer materials in organic solar cell.