Abstract
In this study, strong electron-withdrawing fluorine (F) and cyano (CN) substituents are selectively incorporated into the quinoxaline unit of two-dimensional (2D) D–A-type polymers to investigate their effects on the photovoltaic properties of the polymers. To construct the 2D polymeric structure, electron-donating benzodithiophene and methoxy-substituted triphenylamine are directly linked to the horizontal and vertical directions of the quinoxaline acceptor, respectively. After analyzing the structural, optical, and electrochemical properties of the resultant F- and CN-substituted polymers, labeled as PBCl-MTQF and PBCl-MTQCN, respectively, inverted-type polymer solar cells with a non-fullerene Y6 acceptor are fabricated to investigate the photovoltaic performances of the polymers. It is discovered that the maximum power conversion efficiency of PBCl-MTQF is 7.48%, whereas that of PBCl-MTQCN is limited to 3.52%. This significantly reduced PCE of the device based on PBCl-MTQCN is ascribed to the formation of irregular, large aggregates in the active layer, which can readily aggravate the charge recombination and charge transport kinetics of the device. Therefore, the photovoltaic performance of 2D quinoxaline-based D–A-type polymers is significantly affected by the type of electron-withdrawing substituent.
Highlights
In this study, strong electron-withdrawing fluorine (F) and cyano (CN) substituents are selectively incorporated into the quinoxaline unit of two-dimensional (2D) D–A-type polymers to investigate their effects on the photovoltaic properties of the polymers
The preparation routes for the monomers and polymers are shown in Fig. 1, and their synthetic details and analytical results are described in the experimental section of the Electronic Supporting Information (ESI)
Two-dimensional quinoxaline-based D–A type polymers of PBCl-MTQF and PBCl-MTQCN, in which the strong electron-withdrawing substituents of F and CN units were selectively incorporated, respectively, were synthesized via the Stille coupling reaction to investigate their effects on the photovoltaic properties of the polymers
Summary
Strong electron-withdrawing fluorine (F) and cyano (CN) substituents are selectively incorporated into the quinoxaline unit of two-dimensional (2D) D–A-type polymers to investigate their effects on the photovoltaic properties of the polymers. In addition to the significant progress in n-type acceptors, the development of p-type polymeric donors with appropriate energy levels, good carrier mobility, and favorable morphologies for realizing high-performance PSCs has been emphasized[9] These polymers typically comprise alternating electron-donating (D) and electronaccepting (A) units along the polymer chain, in which a useful intramolecular charge transfer (ICT) state is readily generated. It was recently discovered that the incorporation of strong electron-withdrawing substituents into D and/or A units can efficiently improve the photovoltaic performance of the corresponding D–A-type p olymers[12,13,14] In this regard, several quinoxaline-based D–A-type polymers possessing electron-withdrawing substituents have been investigated to achieve high-performance nonfullerene P SCs15–18. More systematic studies associated with this interesting topic are still required because the effects of the electron-withdrawing substituents on the photovoltaic properties of the polymers are highly susceptible to the chemical composition and configuration of the polymer structure
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