Perovskite solar cells (PSCs) have attracted considerable attention due to their high power conversion efficiency (PCE), cost-effective manufacturing processes, as well as the potential flexibility. However, a significant challenge to the commercial applications of PSCs is their mechanical reliability. In this work, three naphthalene diimide polymers with distinct donor units are chosen to reduce surface trap states and enhance the long-term stability and mechanical reliability of photovoltaic devices. The champion rigid PSCs incorporating conjugated polymers achieved a 373% increase of adhesion toughness at the interface, with a champion PCE of 25.5% for a 0.16 cm(2) single cell and 22.3% for a 30.9 cm(2) module and retain 97% of the initial efficiency after 2000 h of continuous light soaking. Especially, the flexible PSCs exhibited improved mechanical stability, achieving a champion PCE of 24.8% for a 0.16 cm(2) single cell and 20.3% for a 27.9 cm(2) module, maintaining 95% of the initial efficiency after 5,000 bending cycles. This study highlights the potential of interfacial conjugated polymer in enhancing the efficiency and stability of PSCs.