Catalyst-Free, Fast, and Tunable Synthesis for Robust Covalent Polymer Network Semiconducting Thin Films

Covalent polymer networks (CPNs) are of great technological interest due to their robustness and tunability; however, they are rarely applied as semiconductors in optoelectronic devices due to poor material processability. Herein, a simple, rapid, and powerful approach is reported to prepare CPN thin films based on an in situ thermal azide–alkyne cycloaddition (TAAC) in the absence of catalyst or solvent. The method is demonstrated with perylenediimide and triazine‐based monomers, and affords smooth and homogenous CPN films through solution processing and heat treatment (10 min). Moreover, the site‐specific TAAC realizes semiconducting CPNs without undesired impurities or byproducts, and tunable optoelectronic properties are achieved by varying the reaction temperature, which affects the intermolecular self‐assembly. The obtained CPN films exhibit exceptional solvent resistance and good n‐type semiconducting behavior, which together afford application in a series of multilayer solution‐processed organic photovoltaics, where the presence of CPN films significantly improves the solar energy conversion efficiency to over 8% (7% in control devices) when the CPN is used in a planar‐mixed heterojunction device architecture.