Effect of extending fluorinated thiophene π-bridges of BDT- and TT-based polymers for nonfullerene organic solar cells

Optoelectronic analysis of designed semi-circular shaped thiophene-based bridged Y-series NFAs for organic solar cell applications

The highly adaptable optoelectronic and morphological properties of non-fullerene acceptors (NFAs) have made them a prominent research topic in the organic solar cell (OSC) field. This work describes the design of new molecules and investigates the potential optoelectronic aspects of remodified Y-series NFAs endowing with five new semi-circular shaped derivatives (BTPB1-BTPB5) based on the DFT-based quantum simulations. The designed molecules possess higher-lying LUMO energy levels with narrowed bandgaps and excellent coherence between the acceptor and core via inserted bridges. The molecules demonstrate a significant red shift and a wide-ranging absorption spectrum extending from 400 nm to 1500 nm, with the most extensive absorption occurring in the near-infrared (NIR) region. Effective π-π stacking and drastically lower binding energy certify facile charge dissociation and transmission rate. Thiophene-based bridge modification decreased reorganization energy by 47 % which results in facile charge transmission and high current density. Theoretically, simulated PCE is achieved as high as 31.49 % owing to the higher-lying LUMOs. The results demonstrate the value of designing systems and exploring new possibilities for developing effective Y-series NFAs-based high-performance organic solar cells.

Fluorinated Polymer Donors for Nonfullerene Organic Solar Cells

The rapid development of narrow-bandgap nonfullerene acceptors (NFAs) has boosted the efficiency of organic solar cells (OSCs) over 19 %. The new features of high-performance NFAs, such as visible-NIR light absorption, moderate the highest occupied molecular orbitals (HOMO), and high crystallinity, require polymer donors with matching physical properties. This emphasizes the importance of methods that can effectively tune the physical properties of polymers. Owning to very small atom size and strongest electronegativity, the fluorination has been proved the most efficient strategy to regulate the physical properties of polymer donors, including frontier energy level, absorption coefficient, dielectric constant, crystallinity and charge transport. Owing to the success of fluorination strategy, the vast majority of high-performance polymer donors possess one or more fluorine atoms. In this review, the fluorination synthetic methods, the synthetic route of well-known fluorinated building blocks, the fluorinated polymers which are categorized by the type of donor or acceptor units, and the relationships between the polymer structures, properties, and photovoltaic performances are comprehensively surveyed. We hope this review could provide the readers a deeper insight into fluorination strategy and lay a strong foundation for future innovation of fluorinated polymers.