The global energy transition hinges on exceeding the theoretical efficiency limits of single-junction crystalline silicon (c-Si) photovoltaics. Perovskite-Silicon Tandem Solar Cells have emerged as the premier engineering solution, offering a pathway to power conversion efficiencies (PCE) exceeding 34%. This paper explores the critical role of Interface Passivation and the implementation of Textured Silicon Bottom Cells in minimizing optical and electronic losses. We investigate the structural evolution of wide-bandgap metal-halide perovskites and their stability under accelerated aging tests in accordance with 2026 IEC standards. Our results demonstrate that Rubidium and Cesium compositional tuning significantly enhances thermal stability, allowing tandem modules to maintain 95% of their initial PCE after 2,500 hours of continuous operation. This research provides a comprehensive analysis of the "Monolithic Tandem" architecture, providing a technical roadmap for next-generation high-density urban and aerospace solar applications.