Synthesis of multi-armed small molecules with planar terminals and their application in organic solar cells

Bi-armed Cz(BT-T-3Cz)₂, tri-armed TPA(BT-T-3Cz)₃ and tetra-armed SF(BT-T-3Cz)₄ with planar terminals were designed, in which carbazole, triphenylamine and spiro-fluorene units were employed as the electron-rich core, respectively, and benzothiadiazole units were introduced as the electron-deficient arms. As displayed, when the electron-deficient arms in molecules increase, improved thermal properties and increased extinction coefficient were obtained. Also as anticipated, the spatial configurations of SMs could affect their photovoltaic performance significantly. The linear Cz(BT-T-3Cz)₂-based solar cells exhibited a PCE value of 3.0%, however, tri-armed TPA(BT-T-3Cz)₃ and tetra-armed SF(BT-T-3Cz)₄ displayed better photovoltaic properties with the PCE values up to 5.25% and 4.37% in their corresponding devices, respectively, indicating that altering the spatial configurations in molecules is an efficient method to enhance their photovoltaic performance in OSCs.