Molecular Design of Benzothiadiazole Derivatives Electron Acceptors and Matching of Donor-Acceptor Materials

To better understand the relationships between the microstructure and the optoelectronic characteristics of the electron acceptor and to meet the needs of donor-acceptor materials with excellent optical properties for solar cell, a series of acceptor molecules with A′-π-A-π-A′ type are designed.In these molecules, the core framework of benzothiadiazole is used as an acceptor (A), three kinds of conjugated heterocyclics (A′) with different abilities of electron-withdrawing and steric effects are applied as the terminals, and various conjugated structures, such as the double bond, thiophene, benzothiophene and vinyl thiophene, are utilized as π-bridge, respectively.Their geometric configurations, the characteristics of frontier molecular orbital, optical properties, as well as the electronic reorganization energy are predicted by DFT-B3LYP and TD-DFT-CAM-B3LYP.Solvent effects from acetone and chlorobenzene on molecular properties are studied.Furthermore, the Donor-Acceptor (D-A) interfaces are respectively constructed by combining the excellent acceptors with the selected two donors.The DFT-D3 method is used to scan the binding energy of D-A complex, in order to determine the stacked displacement of the interface.The degree of interface recombination is evaluated by calculating electronic coupling (V if ) between HOMO of donors and LUMO of acceptors.The results show that modifying benzothiadiazole with a reasonable substituent is an effective way to adjust LUMO energy levels and lead to the noticeable variation of the energy gap.Combining planar electron acceptor materials (A′-π-A-π-A′ type) with non-planar electron donor materials (D), to form the optical active layer is a practical approach for preventing interface recombination and achieving high open-circuit voltage (V oc ).Considering ΔE L , V if , light absorption efficiency, and solvation effect, D1-1aγ and D1-2aγ combinations are the most promising candidates of optical active layer materials in organic solar cell.