Slow thermal equilibration in methylammonium lead iodide revealed by transient mid-infrared spectroscopy

Tao Xu,Peijun Guo,Jue Gong,Maria K. Y. Chan,Yi Xia,Tze-Bin Song,Mercouri G. Kanatzidis,Sridhar Sadasivam,Constantinos C. Stoumpos,Benjamin T. Diroll,Pierre Darancet,John B. Ketterson,Richard D. Schaller

doi:10.1038/s41467-018-05015-9

Abstract

Hybrid organic–inorganic perovskites are emerging semiconductors for cheap and efficient photovoltaics and light-emitting devices. Different from conventional inorganic semiconductors, hybrid perovskites consist of coexisting organic and inorganic sub-lattices, which present disparate atomic masses and bond strengths. The nanoscopic interpenetration of these disparate components, which lack strong electronic and vibrational coupling, presents fundamental challenges to the understanding of charge and heat dissipation. Here we study phonon population and equilibration processes in methylammonium lead iodide (MAPbI3) by transiently probing the vibrational modes of the organic sub-lattice following above-bandgap optical excitation. We observe inter-sub-lattice thermal equilibration on timescales ranging from hundreds of picoseconds to a couple of nanoseconds. As supported by a two-temperature model based on first-principles calculations, the slow thermal equilibration is attributable to the sequential phonon populations of the inorganic and organic sub-lattices, respectively. The observed long-lasting thermal non-equilibrium offers insights into thermal transport and heat management of the emergent hybrid material class.

Highlights

Hybrid organic–inorganic perovskites are emerging semiconductors for cheap and efficient photovoltaics and light-emitting devices
Our results suggest that classical temperature models and heat transport equations may not be suitable for describing hybrid organic–inorganic perovskites (HOIPs) under large temperature gradients or impulsive lattice heating
The long-lasting thermal non-equilibrium in HOIPs may alter the electronic configuration and contribute to a low thermal conductivity[45,46], which can be especially important in two-dimensional HOIPs47 wherein the organic and inorganic sub-lattices are connected in series

Summary

Introduction

Hybrid organic–inorganic perovskites are emerging semiconductors for cheap and efficient photovoltaics and light-emitting devices. Solution processable hybrid organic–inorganic perovskites (HOIPs) such as methylammonium lead iodide (MAPbI3) represent a research forefront owing to prospects of enhanced performance in solar energy conversion[1], solid-state lighting[2], hard radiation detection[3], and information processing applications[4]. Both HOIPs and their all-inorganic counterparts exhibit superior optoelectronic properties including long carrier diffusion lengths[5], long carrier lifetimes[6], and excellent defect tolerance[7]. Our study provides insights to manipulate such properties for the broader class of organic–inorganic hybrid materials

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Results

Conclusion