Multifunctional Cellulose Derivative Enables Efficient and Stable Wide-Bandgap Perovskite Solar Cells by Inhibiting...

Wide-bandgap (>1.65 eV) perovskites, characterized by their high bromine content, are plagued by severe photo-induced phase segregation, which inflicts irreversible damage on device performance and stability. A primary origin of this degradation is the migration of iodide ions (I^-) and their subsequent conversion to molecular iodine (I₂) under photothermal stress, leading to irreversible performance loss. To address this critical challenge, we report a novel hydrophobically modified cellulose derivative, L12-CMCNa, that through interfacial engineering, markedly enhances the performance and stability of 1.68 eV wide-bandgap perovskite solar cells (PSCs). The functional groups (-COO^- and -OH) of L12-CMCNa anchor at the interface, suppressing iodide ion migration by passivating both uncoordinated Pb^{2 +} defects and iodide vacancies. Concurrently, L12-CMCNa reacts with residual PbI₂ to form an in situ low-dimensional perovskite capping layer. This dual-passivation strategy, combining defect anchoring with the formation of a low-dimensional perovskite barrier, synergistically immobilizes ions at the interface. Consequently, the L12-CMCNa-modified devices deliver a champion power conversion efficiency (PCE) of 23.25% with a fill factor (FF) of 83.80%. Furthermore, the modified devices exhibit exceptional stability. In accordance with ISOS protocols, the unencapsulated devices maintained over 90% of their initial efficiency after 1000 h of continuous one-sun operation (ISOS-L-1I), 800 h of storage at 30% relative humidity (ISOS-D-1), and 1000 h of aging at 65°C (ISOS-D-2I), placing them among the most stable 1.68 eV WBG PSCs reported to date.