Despite the swift rise in power conversion efficiency (PCE) to more than 32%, the instability of perovskite/silicon tandem solar cells is still one of the key obstacles to practical application and is closely related to the residual strain of perovskite films. Herein, a simple surface reconstruction strategy is developed to achieve a global incorporation of butylammonium cations at both surface and bulk grain boundaries by post‐treating perovskite films with a mixture of N,N‐dimethylformamide and n‐butylammonium iodide in isopropanol solvent, enabling strain‐free perovskite films with simultaneously reduced defect density, suppressed ion migration, and improved energy level alignment. As a result, the corresponding single‐junction perovskite solar cells yield a champion PCE of 21.8%, while maintaining 100% and 81% of their initial PCEs without encapsulation after storage for over 2500 h in N2 and 1800 h in air, respectively. Remarkably, a certified stabilized PCE of 29.0% for the monolithic perovskite/silicon tandems based on tunnel oxide passivated contacts is further demonstrated. The unencapsulated tandem device retains 86.6% of its initial performance after 306 h at maximum power point (MPP) tracking under continuous xenon‐lamp illumination without filtering ultraviolet light (in air, 20–35 °C, 25–75%RH, most often ≈60%RH). A surface reconstruction strategy is employed to achieve a strain‐free perovskite film with simultaneously reduced defect density, suppressed ion migration, and improved energy level alignment. The resultant monolithic perovskite/black‐silicon tandem realizes a certified stabilized efficiency ≈29.0%, which is among the best performances for perovskite/silicon tandems based on tunnel oxide passivated contacts.