Enhancing Efficiency and Stability of Perovskite Solar Cells Through Electron-Rich Covalent Organic Frameworks...

Effective regulation of perovskite crystallization is crucial for achieving high-performance perovskite solar cells (PSCs). However, perovskite films typically exhibit low crystallinity and are plagued by abundant bulk and grain boundary defects. Simultaneously controlling crystallization kinetics, defect passivation, and energy level alignment remains a significant challenge. In this study, we designed and synthesized an electron-rich covalent organic framework (COF_FAT) and further introduced N-cationic radicals (COF_Rad) within its framework and pores via a one-step post-treatment. The introduction of these radicals significantly reduced the COFs bandgap, enhanced charge transfer, and minimized open-circuit voltage (V_OC) loss. The ordered COFs structure, featuring multiple coordination sites (Ph-N and N•⁺), modulated the crystallization process and effectively passivated bulk and grain boundary defects, thereby improving the crystallinity of α-perovskite. As a result, PSCs incorporating COF_Rad achieved a remarkable power conversion efficiency (PCE) of 26.33% (certified 25.98%). These devices retained 88% of their initial PCE after 1000 h of thermal aging at 85°C, demonstrating outstanding durability. Moreover, COFs-based PSCs exhibited excellent stability under continuous illumination and humid conditions. This work delivers the highest efficiency reported for COFs-based PSCs to date and offers a new strategy for developing high-performance and stable optoelectronic devices.