Side substitution on benzothiadiazole-based hole transporting materials with a D–A–D molecular configuration for efficient perovskite solar cells

A series of benzothiadiazole-based Donor-Acceptor-Donor (D-A-D) typed hole-transporting materials (HTMs) are designed through introducing electron-withdrawing fluorine group and electron-donating alkoxy group into the core of benzothiadiazole (BT). The energy level alignment, electronic properties, absorption, and hole transport properties of these materials are explored comprehensively using First-principle calculations. As compared with the reference molecule BT, three other substituted molecules have lower HOMO energy levels and lower reorganization energy. Especially, two fluorine substituted hole-transporting materials BT-1F and BT-2F possess planar molecular configuration, suitable energy level, indicating that fluorine substitution is beneficial to the increase of open circuit voltage of device. Moreover, the hole transporting mobility, solubility and stability of all designed molecules are also estimated, which are important items to determine the cost and performance in real application of solar cells. Calculated results show that hole mobility of monofluorinated molecule BT-1F displays relatively higher hole mobility owing to efficient intermolecular interactions. Therefore, molecule BT-1F is likely to be highly efficient HTMs because of its excellent hole mobility and solubility. The present work demonstrates that fluorination engineering on core acceptors in D-A-D typed HTMs is an effective strategy to tune the photovoltaic performance of perovskite solar cells.