Thermal transport in 2D hybrid perovskite single crystals
Date
2020
Authors
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Publisher
University of Delaware
Abstract
Methylammonium lead (II) iodide has recently attracted considerable interestin the field of photovoltaics. It has achieved over 22% efficiency in laboratory devices and also has the potential to make an impact in other technologies such as thermoelectric and optoelectronics. Recently, layered two-dimensional inorganic-organic hybrid compounds have been studied as optoelectronic devices as well. Based on the high density of organic-inorganic interfaces, it is reasonable to hypothesize that these materials may have low thermal conductivity, but the thermal transport properties and physical mechanisms of heat transport have yet to be reported in these materials. How phonons transport across the insulating organic and semiconducting inorganic layer of superlattice structure with atomically abrupt interfaces and how bond strength inthe interfaces of organic layers effect phonon transport require comprehensive mate-rial characterization and experimental investigation. Here we report the synthesis of[(CnH2n+1NH3)2PbI4] (n= 4,5,6,7) solution-grown single crystals, their heat capacity and thermal properties measured by time-domain thermoreflectance. Thermal conductivity measurements by Time Domain Thermoreflectance (TDTR) reveal that as the chain length of alkylammonium is increased fromn= 4 to n= 7 thermal conductivity almost remains the same. Using a Bayesian statistics approach, we show thattransport in alkylammonium lead iodide is unlikely to be explained by interfacial scattering, while also providing statistical bounds on the required interface conductance if it is. We show the required interface conductance would be rather high, 76 MW/m2-K< G <94 MW/m2-K, compared to existing literature on inorganic-organic interfaces.Given this and given that models based on incoherent scattering at interfaces predict linear to super linear scaling of the thermal conductivity with chain length, we conclude that phonons likely carry an appreciable portion of the heat across the interface coherently, and are not limited by the weak interfaces present.
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Keywords
Photovoltaics, Methylammonium lead iodide