Crystallographic and Stoichiometric Control of ALD‐SnO ₂ Interconnects for Efficient Flexible Perovskite‐organic‐tandem Photovoltaics

Perovskite‐organic‐tandem photovoltaics (POT‐PVs) are a promising next‐generation photovoltaic technology, offering low‐cost solution processability, tunable bandgap alignment, and high subcell compatibility. However, the interconnect layer remains a major bottleneck due to (i) solvent‐induced degradation from the aqueous PEDOT:PSS used in organic subcells, (ii) poor energetic alignment and inefficient carrier recombination at the interface, and (iii) instability arising from insufficiently dense or chemically unstable interlayers. In this work, we address these challenges by engineering atomic layer deposited SnO 2 as the interconnect layer via temperature‐controlled crystallization, which tunes surface energy to expose low‐energy crystalline facets and modulates the film's stoichiometric composition. This chemi‐electronic control establishes an energetically well‐aligned and electrically benign heterojunction between the perovskite bottom cell and the organic top cell, forming a compact, chemically stable interface that supports robust top‐cell fabrication. As a result, without sacrificing the performance of the subcells, we demonstrate a power conversion efficiency of 25.90% (certified 25.47%) for rigid POT‐PVs and 24.39% for flexible tandem devices, elevating the performance of flexible POT‐PVs to a level comparable to that of rigid, highlighting the promise of this strategy for high‐efficiency flexible photovoltaics. Meanwhile, the 1.80 eV perovskite subcell achieves a recorded efficiency of 20.58%, highlighting the compatibility of this work.