Structural Evolution in Methylammonium Lead Iodide CH3NH3PbI3

The organic–inorganic hybrid perovskite, in particular, methylammonium lead iodide (MAPbI3), is currently a subject of intense study due to its desirability in making efficient photovoltaic devices economically. It is known that MAPbI3 undergoes structural phase transitions from orthorhombic Pnma to tetragonal I4/mcm at ∼170 K and then to cubic Pm3m at ∼330 K. A tetragonal P4mm phase is also reported at 400 K considering total cation disorder is not appealing due to its hydrogen-bonding capabilities. Resolving this ambiguity of phase transition necessitates the study of the structural evolution across these phases in our work using ab initio methods. In this work, we show that the structural phase evolves from Pnma to I4/mcm to P4mm to Pm3m with increasing volume. The P4mm phase is a quasi-cubic one with slight distortion in one direction from cubic Pm3m due to the rotation of MA cations. Biaxial strain on MAPbI3 reveals that only the Pnma and P4mm phases are energetically stable at a ...