Two star-shaped small molecule donors based on benzodithiophene unit for organic solar cells

Star-shaped small molecules have attracted great attention for organic solar cells (OSCs) because they have three-dimensional charge-transport characteristics, strong light absorption capacities and easily tunable energy levels. Herein, three- and four-armed star-shaped small molecule donors, namely BDT-3Th and BDT-4Th, respectively, have been successfully designed and synthesized, which used benzodithiophene (BDT) as the central unit. The two star-shaped intermediates (2a and 2b) could be simultaneously obtained by one-step of Suzuki coupling, and 1,2-dimethoxyethane played a key role in the Suzuki coupling. Both of them have excellent thermal stability, good solubility and broad absorption. Four-armed BDT-4Th shows a slightly higher extinction coefficient, a deeper HOMO energy level and an obviously better phase separation morphology when blended with Y6 than three-armed BDT-3Th. As a result, increased power conversion efficiency (PCE) of 5.83% is obtained in the BDT-4Th:Y6-based OSC devices, which is obviously higher than that of the BDT-3Th:Y6-based devices (PCE = 3.78%). To the best of our knowledge, this is the highest PCE among the EDT-based star-shaped donors-based OSCs. This result provides an effective strategy to obtain star-shaped small molecule donor materials for high efficient organic solar cells. (C) 2021 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.

Automated summary

Star-shaped small molecules with three-dimensional charge-transport characteristics have been successfully designed and synthesized for use in organic solar cells. When blended with Y6, the four-armed star-shaped molecule BDT-4Th demonstrated higher conversion efficiency compared to the three-armed BDT-3Th, providing an effective strategy for achieving high efficiency in organic solar cells.