<p>Perovskite solar cells provide an economically viable and highly efficient pathway to harness solar energy. However, the instability of the organic component in hybrid perovskites presents a fundamental challenge that constrains the longevity and performance of perovskite photovoltaics. In this study, we introduce a molecular deuteration strategy to stabilize FAPbI₃ perovskite by replacing the active hydrogen in the N–H bond with its heavier isotope, deuterium. The reduced ground-state energy of the isotopic N–D bond induces a deuteration kinetic isotope effect, which significantly decreases the rate constant of the deprotonation reaction from 5.15 × 10⁻⁸ to 2.42 × 10⁻⁸ s⁻¹. Solar cells fabricated using deuterated FAPbI₃ thin films achieve a power conversion efficiency of 25.08% and exhibit a <i>T</i>₉₇ lifetime of 1264 h under continuous one-sun illumination at 55 °C. This approach paves the way for developing inherently stable perovskite materials and extending the operational lifespan of solar cell devices.</p>