The crucial role of density functional nonlocality and on-axis CH3NH3 rotation induced I2 formation in hybrid organic-inorganic CH3NH3PbI3 cubic perovskite

Vichawan Sakulsupich,Udomsilp Pinsook,Thiti Bovornratanaraks,Rakchat Klinkla,Teerachote Pakornchote

doi:10.1038/s41598-018-31462-x

Vichawan Sakulsupich, Udomsilp Pinsook + Show 3 more

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https://doi.org/10.1038/s41598-018-31462-x

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Abstract

Effects of electronic nonlocality in density functional theory study of structural and energetic properties of a pseudocubic CH3NH3PbI3 are investigated by considering coherent rotation around C–N axis of a CH3NH3 cation. A number of truly non-local and semi-local exchange correlation density functionals are examined by comparing calculated structural parameters with experimental results. The vdW-DF-cx which takes into account the non-local van der Waals correlation and consistent exchange shows the best overall performance for density functional theory study of this system. Remarkable distinctions between results from vdW-DF-cx and those from PBEsol exchange correlation functionals are observed and indicate the need of including the non-local interaction in the study of this system, especially its dynamical properties. The obtained rotational barriers are 18.56 meV/formula and 27.71 meV/formula which correspond to rotational frequencies of 3.71 THz and 2.60 THz for vdW-DF-cx and PBEsol calculations, respectively. Interestingly, the maximally localised Wannier function analysis shows the hydrogen bonding assisted covalent character of two iodide anions at a moderate rotational angle which can lead to I2 formation and then material degradation.

Highlights

In the last decade, there has been a booming interest in hybrid organic inorganic perovskites (HOIPs) originates from their potential applications in optoelectronic, thermoelectric, and photovoltaic technologies, owing to their favourable electronic, excitonic and optical properties[1,2,3,4]
The average values of such calculated parameters, i.e. average lattice constant (a), average Pb-I bond length over three inequivalent I-atoms (PbI), average C-H bond length (CH), average N-H bond length (NH), and C-N bond length (CN) obtained by performing full structural relaxation, there is no any constraint, where the C-N axis is at the lowest enthalpy arrangement[14], are used for the comparison with Weller et al.’s accurate powder neutron diffraction experimental results[15]
The structural parameters are grouped into two subgroups according to magnitudes of their absolute errors, i.e. a and PbI as one subgroup and CN, CH and NH as the other

Summary

Introduction

There has been a booming interest in hybrid organic inorganic perovskites (HOIPs) originates from their potential applications in optoelectronic, thermoelectric, and photovoltaic technologies, owing to their favourable electronic, excitonic and optical properties[1,2,3,4]. Methylammonium lead iodide (MAPbI3) perovskite, which, as the name suggested, has methylammonium (MA) as the cation, is regarded as the archetype of HOIPs since it exhibits rich fundamental photovoltaic properties, and has recently been intensively studied and developed for solar cell devices. Recent experimental results suggest that there exist two kinds of dynamics associated with a MA cation in MAPbI323. The second type is the much faster methyl and/or ammonium groups rotation about C-N axis with sub-picosecond time scale[25] that has recently been estimated at ~30 times faster[26]. Such fast-rotation cannot be precisely probed by experiments[23]. The interplay between octahedron tilting and the MA dynamics still needs a clearer understanding, as it has recently been dubbed as the chicken-and-egg paradox by Li and Rinke[27]

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