Impact of silicon substrate topography on sequentially evaporated perovskite film growth

Thermal evaporation offers a scalable and solvent-free pathway for transitioning perovskite from laboratory prototypes to industrial production, yet it remains significantly underexplored. In this work, we present the first fully solvent-free top cell in a 2-terminal perovskite-silicon tandem solar cell. We systematically explore the structural and morphological evolution of sequentially evaporated perovskite films and the impact of silicon substrate topography on the perovskite film formation. Using in situ X-ray diffraction (XRD), we observed an enhanced conversion of lead halides to perovskite on micro-textured substrates compared with planar substrates. Correspondingly, morphological characterizations revealed a compact layer of lead halides on planar substrates compared with a porous one on textured substrates. Alongside this, an initial layer-by-layer deposition of lead halides is observed, followed by interlayer mixing after adding formamidinium iodide (FAI). These insights advance the understanding of sequential thermal evaporation and enable fully solvent-free perovskite-silicon tandem solar cells with a stabilized power conversion efficiency of 27.0 % .