Two‐Dimensional Surface Passivation with Distinct Cations Enabling High Efficiency and Mechanical Durability in Flexible Perovskite Solar Cells

Recent advancements in flexible perovskite solar cells (f-PSCs) have significantly improved power conversion efficiency (PCE) and mechanical durability, particularly when using a polyethylene naphthalate (PEN) substrate. Herein, the effects of 2D organic surface treatments-including phenylethylammonium iodide (PEAI), 5-ammonium valeric acid iodide (5-AVAI), and butylammonium iodide (BAI)-on the photovoltaic performance and mechanical properties of f-PSCs are investigated. The findings reveal that radiative voltage losses near the band edge are minimal for 2D-BAI (0.032 V) and 2D-PEAI (0.027 V) but significantly higher for 2D-5AVAI (0.136 V). After 2D-BAI treatment, the average Young's modulus increases to 0.48 GPa, reaching a maximum of 2 GPa, reinforcing the mechanical resilience of the perovskite layer. Consequently, 2D-BAI-treated f-PSCs achieve a PCE of 19.81% while maintaining structural integrity after 10,000 bending cycles. This study underscores the effectiveness of 2D treatments in simultaneously enhancing both device efficiency and durability, offering valuable insights for the development of robust and flexible electronic devices.