5 years ago

First-Principles Prediction of a Stable Hexagonal Phase of CH3NH3PbI3

First-Principles Prediction of a Stable Hexagonal Phase of CH3NH3PbI3
Xing Huang, Arashdeep Singh Thind, Rohan Mishra, Jianwei Sun
Methylammonium lead iodide (CH3NH3PbI3 or MAPbI3) perovskite is a promising new photovoltaic material with high power conversion efficiency. However, its perovskite phase with corner-connected PbI6 octahedra shows poor environmental stability. More recently, MAPbI3 has been shown to be thermodynamically unstable with a positive formation enthalpy. Here, using first-principles density functional theory calculations, we predict a layered hexagonal phase of MAPbI3 consisting of infinite chains of face-shared PbI6 octahedra with P63mc space-group symmetry to be thermodynamically the most stable phase for a wide range of volume and temperature compared to any of the experimentally observed perovskite phases with a different tilt pattern of the corner-connected octahedra. The predicted hexagonal phase is also dynamically stable without any soft phonon modes. The change from corner to face-shared connectivity in the hexagonal phase leads to a predicted band gap of 2.6 eV and a band structure that favors highly anisotropic charge transport.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b01781

DOI: 10.1021/acs.chemmater.7b01781

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