Exploring the photovoltaic properties of promising non-fullerene symmetric acceptors due to fluorine substitution of central units

• 1、Faculty of Materials and Energy, Southwest University, Chongqing 400715

Abstract：Similar to halogenation of the terminal groups, the strategy of symmetric modification of central units has also become popular for designing new photovoltaic materials and shown dramatic effects in improving photovoltaic properties. Whereas, how halogenation of central units with varying degrees of ring fusion of small-molecule non-fullerene acceptor(SM-NFA) influences opt-electric properties is still not very clear. Focusing on two prospective SM-NFAs Qx-1 and Qx-2 with varying degrees of ring fusion on central units, we further designed seven additional new molecules through fluorination of the central units. By applying density functional theory (DFT) and time-dependent DFT calculations to our interested research, we systematically explore the impact of altered fluorinated location and the effects of fluorination in different degrees of ring fusion of central units on the opt-electric properties. We find that the halogenations of central units may significantly affect the molecular planarity, dipole moment, electrostatic potential (ESP), exciton binding energy, energy loss, and absorption spectrum. Moreover, the concentration of ESP value may influence the photovoltaic properties. Consequently, fluorination influences Qx1 series more than Qx2 series while molecules in Qx2 series all perform better than those in Qx1 series. Newly designed Qx2-cf exhibits enhanced molecular planarity and electrostatic potential, highlighting its potential as a promising SM-NFA. Therefore, we discover an up-and-coming direction for the design of SM-NFA.

Keywords： Organic Solar Cells Non-fullerene acceptor Halogen substitution UV-Vis absorption spectra DFT/TDDFT