Internal Encapsulation Enables Efficient and Stable Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) have made significant strides in efficiency, but their long‐term stability remains a challenge. While external encapsulation mitigates extrinsic degradation and lead leakage, it does not fully address performance decline due to ion migration within the perovskite devices. Therefore, an internal encapsulation layer that can selectively transport charge carriers and suppress ion migration across the interface is of great significance for achieving long‐term stability in these devices. Here, polytetrafluoroethylene (PTFE) can serve as an effective internal encapsulation layer between the perovskite film and the electron transport layer in the inverted PSCs is demonstrated. The PTFE layer can selectively transport electrons and suppress ion diffusion, resulting in a higher power conversion efficiency (PCE) of 25.49% compared to 24.74% of the control devices and much better long‐term stability. Even after 1500 h of air exposure, the internal encapsulated perovskite devices can maintain 92.6% of their original PCE, outperforming the control devices at 80.4%. This approach offers a novel solution for addressing ion migration‐induced instability in perovskite devices.