Perovskite solar cells (PSCs) have attracted much attention due to their rapidly increased power conversion efficiencies, however, their inherent poor long-term stability hinders their commercialization. The degradation of PSCs first comes from the degradation of hole transport materials (HTMs). Here, we report the construction of periodic π-columnar arrays and ionic interfaces over the skeletons by introducing cationic covalent organic frameworks (C-COFs) to the HTM. Periodic π-columnar arrays can optimize the charge transport ability and energy levels of the hole transport layer and suppress the degradation of HTM, and ionic interfaces over the skeletons can produce stronger electric dipole and electrostatic interactions, as well as higher charge densities. The C-COFs were designed and synthesized via Schiff base reaction by using 1,3,5-triformylphloroglucinol as a neutral knot and dimidium bromide as cationic linker. The neutral COFs (N-COFs) were also synthesized as a reference by using 3,8-diamino-6-phenylphenanthridine as neutral linker. PSCs with cationic COF exhibit the highest efficiency of 23.4% with excellent humidity and thermal stability. To the best of our knowledge, this is the highest efficiency among the meso-structured PSCs fabricated by a sequential process.

Developing agents that can accurately differentiate tumors from normal healthy tissues is of utmost importance for safe cancer therapy. Active targeting has been considered as an effective technique for tumor recognition. In this work, we demonstrate a folate-functionalized nanoscale covalent organic framework (FATD nCOF) highly specific to cancer cells through active targeting of their enriched folate receptors (FRs). The FATD nCOF prepared by simple post-synthetic modification of the COF surface defeats disperses well in water and exhibits a high loading capacity for various anticancer drugs. The biocompatible FATD nCOF is selectively internalized by FR-harboring cancer cells and consequently augments the efficacy of the loaded drug, Withaferin A (Wi-A), for targeted cancer cell killing. In biomolecular mechanism studies, Wi-A-loaded FATD (FATD@Wi-A) nanocomposites show remarkably a higher rate of apoptosis in FR-enriched cancer cells. Comparative analyses of FR-positive and FR-negative tumor xenografts reveal enhanced selective antitumor activity of FATD@Wi-A nanotherapeutics. Taken together, the study findings suggest that FATD nCOF holds great promise for active targeting of tumors in vivo. Our simple yet effective technology might be valuable for creating new state-of-the-art COFs for chemical and biomedical applications.