Polar rotor scattering as atomic-level origin of low mobility and thermal conductivity of perovskite CH3NH3PbI3

Abstract

Perovskite CH3NH3PbI3 exhibits outstanding photovoltaic performances, but the understanding of the atomic motions remains inadequate even though they take a fundamental role in transport properties. Here, we present a complete atomic dynamic picture consisting of molecular jumping rotational modes and phonons, which is established by carrying out high-resolution time-of-flight quasi-elastic and inelastic neutron scattering measurements in a wide energy window ranging from 0.0036 to 54 meV on a large single crystal sample, respectively. The ultrafast orientational disorder of molecular dipoles, activated at ∼165 K, acts as an additional scattering source for optical phonons as well as for charge carriers. It is revealed that acoustic phonons dominate the thermal transport, rather than optical phonons due to sub-picosecond lifetimes. These microscopic insights provide a solid standing point, on which perovskite solar cells can be understood more accurately and their performances are perhaps further optimized.

Direct evidence of weakly dispersed and strongly anharmonic optical phonons in hybrid perovskites

“…Similarly in MAPI, we obtained two low-energy modes located at 2.3 and 3.8 meV, an intense peak centered at 11.7 meV surrounded by two smaller shoulders at 10.8 and 12.8 meV followed by two bundles at 15.5 and 18.3 meV, and at higher energy range, other ones at 23.5, 28.5 and 38.3 meV ( Figure 3.c,d). These again are directly comparable with previous INS studies [50,55] where two additional small modes in the 2-5 meV range (∼3.1 and ∼4.3 meV) were reported.…”

Recent Progress in Single‐Crystalline Perovskite Research Including Crystal Preparation, Property Evaluation, and Applications

“…Over the last 2 years, an increasing number of researchers have begun studying single‐crystalline perovskites, including crystal preparations,21, 27, 28, 43, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65 property studies,21, 27, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80 and applications 56, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91. For example, an extremely long carrier lifetime (up to 20 µs) and carrier diffusion length (175 µm) have been found,21 which has received a great deal of attention.…”

Influence of Chloride Substitution on the Rotational Dynamics of Methylammonium in MAPbI3–xClx Perovskites

“…The phonons were modelled in the momentum integrated IN5 data in the range between 30 meV and 1.5 meV using Lorentzian functions (Fig. 3, S3 35,36 Furthermore, the model also includes a Lorentzian function at 0 meV to map the influence of quasielastic scattering components. A complete summary of the determined lattice vibrations is given in Table S1 and S2.…”

“…and Li. 13,36 For the orthorhombic phase, Chen and coworkers proposed that the quasielastic contribution can be described with only one quasielastic component QISF C3 so that EISF = 1 -QISF C3 (C 3 model). 13 The quasielastic contribution is described by a Lorentzian function L C3 with QISF C3 = 12 where j 0 is the zeroth-order spherical Bessel function and r√3 = − = 1.72 Å is the averaged distance between two hydrogen atoms in each of the methyl and ammonium groups.…”