Highly Conjugated Three-Dimensional Covalent Organic Frameworks Based on Spirobifluorene for Perovskite Solar Cell Enhancement

Highly conjugated three-dimensional covalent organic frameworks (3D COFs) were constructed based on spirobifluorene cores linked via imine bonds (SP-3D-COFs) with novel interlacing conjugation systems. The crystalline structures were confirmed by powder X-ray diffraction and detailed structural simulation. A 6- or 7-fold interpenetration was formed depending on the structure of the linking units. The obtained SP-3D-COFs showed permanent porosity and high thermal stability. In application for solar cells, simple bulk doping of SP-3D-COFs to the perovskite solar cells (PSCs) substantially improved the average power conversion efficiency by 15.9% for SP-3D-COF 1 and 18.0% for SP-3D-COF 2 as compared to the reference undoped PSC, while offering excellent leakage prevention in the meantime. By aid of both experimental and computational studies, a possible photoresponsive perovskite SP-3D-COFs interaction mechanism was proposed to explain the improvement of PSC performance after SP-3D-COFs doping.