All‐in‐One Hollow Flower‐Like Covalent Organic Frameworks for Flexible Transparent Devices

Abstract Covalent organic frameworks (COFs) exhibit great potential in the application of functional electronic devices. However, there has been no report of the precise fabrication of 3D all‐in‐one hollow micro/nanostructures based on COFs. Here, for the first time, all‐in‐one hollow dioxin‐based COF‐316 microflowers are synthesized measuring 5–7 µm and with interconnected hollow petals through a self‐template strategy. The growth mechanism involves the collaborative process of self‐assembly of nanoparticles, inside‐out Ostwald ripening, and epitaxial growth. Due to the intrinsic porosity and interconnected hollow structure, COF‐316 can uniformly composite with polypyrrole (PPy) through the “interior” and “exterior” functionalization, in which the hydrogen bond interaction enhances the charge transfer efficiency and structural stability in the charge/discharge process. The COF‐316@PPy flexible transparent supercapacitors exhibit an areal specific capacitance (C_A) of 783.6 µF cm^–2 at 3 µA cm^–2 and long‐term cycling stability. This work will boost research on the valuable design concepts of 3D hollow COF materials for energy storage devices.