Efficient and stable perovskite solar cells by build-in π-columns and ionic interfaces in covalent organic frameworks

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.