Identifying and Overcoming the Polaron-Induced Mobility Limit in a 2D Germanium Halide Perovskite.
basic_science · Level V
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- Record sourced from PubMed, PMID 41653466.
- Also identified by DOI 10.1021/acsnano.5c18264.
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Abstract
Germanium-based halide perovskites (GHPs) are promising nontoxic alternatives to their lead-based counterparts, yet their charge transport properties remain poorly understood. Probing the intrinsic mobility of these materials has been challenging due to the lack of single-crystal devices. Here, we report the fabrication of single-crystal field-effect transistors from a 2D Ruddlesden-Popper GHP, (PEA)<sub>2</sub>GeI<sub>4</sub>. Temperature-dependent measurements reveal that its intrinsic charge transport is thermally activated (∂μ/∂<i>T</i> > 0), a hallmark of small polaron hopping, which stands in stark contrast to the band-like transport (∂μ/∂<i>T</i> < 0) of its tin-based analogue ((PEA)<sub>2</sub>SnI<sub>4</sub>). We provide direct spectroscopic evidence that this behavior is driven by exceptionally strong electron-phonon coupling in the GHP lattice. Critically, we validate this by demonstrating that rational cation engineering to suppress this coupling switches the transport mechanism back to the more efficient band-like regime, enhancing mobility by over an order of magnitude. This work not only identifies small polaron formation as the primary performance limit in GHPs but also demonstrates a clear strategy to overcome it, contributing to the rational design of high-performance, nontoxic perovskite optoelectronics.