Rationally regulating the terminal unit and copolymerization spacer of polymerized small-molecule acceptors for all-polymer solar cells with high open-circuit voltage over 1.10 V

Abstract

Recently, great advances in polymerized small molecular acceptors (PSMAs) have boosted the power conversion efficiencies (PCEs) of all-polymer solar cells (all-PSCs) over the 17% milestone. However, significant research efforts have been mainly dedicated to designing narrow bandgap PSMAs by altering the building block and alkyl side chain. In this work, we report the design of novel PSMAs with wide bandgaps by incorporating a novel terminal unit without isomerization, 5-bromo-4,7-difluoro-1H-indene-1,3(2H)-dione (FFOBr). The resulting PSMAs exhibit high molar absorption coefficient over 10⁵ M⁻¹ cm⁻¹, relatively wide bandgaps about 1.65 eV as well as high-lying lowest occupied molecular orbital (LUMO) energy levels of above −3.70 eV. When matching with the polymer donor JD40, both polymer acceptors can enable efficient all-PSCs with over 1.10 V open-circuit voltage (V_OC) due to their high-lying LUMO energy level. Moreover, with a screened copolymerization spacer, the PFFO-Th-based blend film exhibits favorable morphology, more ordered crystallization, improved charge transport, and reduced recombination losses, which together contribute to the higher short-circuit current density and fill factor and thereby a high PCE of 10.8%. This value is one of the best with regard to PSMA-based all-polymer solar cells with V_OC over 1.10 V in the reported literature. Our work shows that the terminal unit and linkage manipulation are effective strategies to develop high-performance PSMAs with controllable bandgaps.