Two-dimensional
(2D) hybrid organic–inorganic perovskites
consisting of alternating organic and inorganic layers are a new class
of layered structures. They have attracted increasing interest for
photovoltaic, optoelectronic, and thermoelectric applications, where
knowing their thermal transport properties is critical. We carry out
both experimental and computational studies on thermal transport properties
of 2D butylammonium lead iodide crystals and find their thermal conductivity
is ultralow (below 0.3 W m–1 K–1) with very weak anisotropy (around 1.5) among layered crystals.
Further analysis reveals that the unique structure with the preferential
alignment of organic chains and complicated energy landscape leads
to moderately smaller phonon lifetimes in the out-of-plane direction
and comparable phonon group velocities in in-plane and out-of-plane
directions. These new findings may guide the future design of novel
hybrid materials with desired thermal conductivity for various applications.
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