Improved photovoltaic performance of star-shaped molecules with a triphenylamine core by tuning the substituted position of the carbazolyl unit at the terminal

Two star-shaped molecules of TPA(BT–2Cz)3 and TPA(BT–3Cz)3 with a triphenyl-amine (TPA) core were designed and synthesized, in which 2- and 3-carbazolyl units (2Cz and 3Cz) are attached to the benzothiadiazole (BT) arms as planar terminal groups, respectively. Although both molecules show a similar broad UV-Vis absorption covering from 300 nm to 560 nm, different photovoltaic performances were observed owing to the varied linked positions of terminal carbazolyl units. In contrast to TPA(BT–2Cz)3-based solar cells, solution-processable organic solar cells (OSCs) based on TPA(BT–3Cz)3 exhibited better photovoltaic performance with the maximum power conversion efficiency up to 3.94% and an enhanced short-circuit current of 8.80 mA cm−2. This work further demonstrates that tuning the substituted position of the terminal carbazolyl group can significantly improve the photovoltaic performance of its resulting small molecules.