Functionalized sp² Carbon-Conjugated Covalent Organic Frameworks for Interfacial Modulation of Inverted Perovskite Solar Cells

Interfacial modulation utilizing functional materials is proven to be crucial for obtaining high photovoltaic performance in lead halide perovskite solar cells (PSCs). This study investigates, for the first time, the utilization of a pyrene-based sp² carbon-conjugated covalent organic framework (sp²c-COF) as an interfacial layer in inverted PSCs. Functionalized with cyano (–CN) Lewis base groups, the sp²c-COF exhibits a dual effect, simultaneously passivating both the NiO_x and the perovskite layers. Detailed characterization results highlight the role of sp²c-COF in reducing the Ni³⁺ defect density in NiO_x films and forming Lewis acid-base adducts with undercoordinated Pb²⁺ on the perovskite surfaces, thereby inhibiting interfacial redox reactions and suppressing non-radiative recombination. Moreover, sp²c-COF leads to improved crystallinity of perovskite films. Benefiting from the synergistic effects, sp²c-COF-modified devices delivered a champion efficiency of 17.64%. These findings underscore the potential of sp²c-COF as a functional interface material for PSCs, offering enhanced efficiency and stability. The study contributes to advancing the understanding and application of covalent organic frameworks in photovoltaic technologies.