An n-Type Benzobisthiadiazole-Based Covalent Organic Framework with Narrowed Bandgap and Enhanced Electroactivity

Low-bandgap covalent organic frameworks (COFs) emerge as one of the most intriguing conjugated polymers for the development of electronic devices, while they often lack desirable electron affinity, thereby compromising the activity and stability in electrochemical transformation. Here, we report an n-type semiconducting two-dimensional (2D) COF, featuring a low bandgap (1.36 eV) and strong electron affinity (4.41 eV) as well as high crystallinity and porosity. The columnar stacking array of the benzobisthiadiazole moiety in 2D COFs plays a critical role in elevating electroactivity. It not only leads to the outstanding electrical conductivity and air stability upon reductive doping but also enables the boost of transformation kinetics for polysulfides on the separators of lithium–sulfur batteries causing a higher capacity and better cycling performance. The design strategy underpins the versatile development of electroactive COF materials with desirable electronic properties and promotes their applicability in energy storage and electronics.