The authors describe a method of vapor deposition of a perovskite absorber on industrially structured (micrometer pyramidal) silicon wafers that allows conformal and balanced deposition of the organic precursors required for high-quality perovskite films.[1][2] The process added trace amounts of methylenediammonium dichloride, which is converted to the cyclic cation tetrahydrotriazinium (THTZ-H+) during in situ crystallization, which is incorporated into the perovskite lattice.[2] This cation forms strong multidimensional hydrogen bonds with iodide ions in the perovskite structure, thereby reducing defects and improving film homogeneity.The result is improved phase stability of perovskite with a bandgap of approximately 1.68 eV under long-term light and high temperature loading (1-sun at 85 °C).[A monolithic perovskite/silicon tandem cell with this approach achieved an independently certified efficiency of 33.7% over an area of 1 cm2.[2] Stability tests have shown operational stability well in excess of 2,000 hours and T90 (time to power drop to 90% of initial value) of more than 1,400 hours at 85 °C under 1-sun illumination in vapor deposition experiments on industrial wafers.[1][1] The authors also substantiate that a special molecule binding to the silicon surface improves the adsorption of organic precursors during vapor deposition, thus solving the problem of non-uniform deposition on steep wafer textures.1][2] The findings demonstrate the compatibility of vapor deposition with industrial silicon structures and significant improvements in efficiency and thermal stability for realistic tandem cell deployments.[1][2] The authors also show that the