Efficient Polymer Solar Cells Facilitated by Halogenated Substituted Wide‐Bandgap Polymers and a Backbone Twisted Low‐Bandgap Acceptor

Abstract

AbstractDuring the past five years, plentiful efficient polymer solar cells (PSCs) developed rapidly with the application of small molecules as non‐fullerene acceptors (NFAs). Although most of the synthesized NFAs have planar backbones, the backbone twisted NFAs have exhibited impressive performances in devices with wide‐bandgaps polymer donors like J52 and PBDB‐T. To boost the performances of PSCs based on NFAs with contorting backbone, a systematic study of a twisted NFA (i‐IEICO‐4F), with J52 and its halogenated counterparts was conducted, because the attached halogen atoms have strong effects on the frontier molecular orbitals and the aggregation properties of the polymers. Despite the polymers possessing similar absorption spectra, they exhibited continuously deepened molecular energy levels. Among the three polymers, the device based on J52‐2F and i‐IEICO‐4F achieved the lowest efficiency of 11.78 %. Although differed in open‐circuit voltages and short‐circuit current densities, the J52‐ and J52‐2Cl‐based devices successfully acquired enhanced fill factors of 67.0 % and 67.6 %, giving rise to enhanced efficiencies of 12.47 % and 12.69 %. The superior performance of J52‐2Cl‐based device stems from its deepened molecular energy levels, improved charge transport properties, and better morphological features, demonstrating the important influence of halogenation substitution on the characteristic regulation of wide‐bandgap conjugated polymers for high‐performance PSCs.