Two Birds with One Stone: Minimizing Voltage Deficit via Three Moieties of F, COOH, and NH₂ of Carbon Dots Modifying the SnO₂ Electron Transport Layer and Buried Interface for Flexible Perovskite Solar Cells

Flexible perovskite solar cells (F-PSCs) have demonstrated remarkable potential for next-generation wearable platforms. Nonetheless, the reduction of open-circuit voltage (V_OC) at the interface within F-PSCs poses a significant barrier to improving the photoelectric conversion efficiency (PCE). Herein, we reported an effective “two birds with one stone” strategy by utilizing carbon dots (CDs) as a multifunctional treatment modulator to modify the SnO₂ electron transport layer (ETL) and buried interface. On the one hand, CDs were explored to passivate trap states associated with Sn dangling bonds and oxygen vacancies on SnO₂ surfaces through Lewis acid-base coordination, thereby enhancing the electron mobility of SnO₂ films and facilitating charge extraction from perovskite layers. On the other hand, the functional groups (including carboxyl, fluorine, and amino) on CDs enable the formation of coordination and hydrogen bonding with PbI₂, promoting the formation of high-quality perovskite films with reduced defect densities. The collective enhancements effectively mitigate trap-assisted charge recombination and interfacial energy loss, significantly reducing the device voltage deficit and enabling F-PSCs to attain a PCE of 22.97% with enhanced V_OC from 1.06 to 1.18 V. Notably, CDs-incorporated devices demonstrate exceptional operational durability, maintaining 83% of initial PCE after 400 h of continuous illumination (AM 1.5G) in an air atmosphere and retaining 81% PCE following 4000 cyclic bending tests (6 mm radius). This methodology establishes a robust framework for simultaneously enhancing both the efficiency and stability in FAPbI₃-based F-PSCs.