Impact of Grain Size on Low‐Temperature Carrier Phase Coherence Length in Polycrystalline Halide Perovskite Films

Abstract Halide perovskites are now being studied for a full range of optoelectronic devices due to their excellent electronic and optical properties. This work explores the impact of grain boundaries on low‐temperature carrier transport in polycrystalline cesium tin iodide (CsSnI 3 ) within the quantum diffusive transport regime, comparing a range of polycrystalline samples with varying grain sizes with epitaxial counterparts. Low‐temperature magnetoresistance measurements reveal the presence of weak anti‐localization (spin‐orbit effects) with a shorter coherence length ( L ϕ ) than the epitaxial films. Surprisingly, L ϕ is not found to be impacted by grain size, despite being nearly an order of magnitude larger for the epitaxial samples. Rather, it is found that these differences are largely dictated by the control of the crystal structure (and strain). First‐principle density functional theory (DFT) calculations demonstrate lower phonon density of states (PhDOS) across frequencies in the epitaxial tetragonal phase compared to its less symmetric orthorhombic counterpart in polycrystalline films. This supports the hypothesis of lower electron‐phonon scattering in the single‐domain epitaxial films resulting in longer L ϕ . These findings will likely help in understanding low temperature quantum coherent transport in semiconductors and other halide perovskites, and further develop this material class for quantum device applications.