First-principles study of lead iodide perovskite tetragonal and orthorhombic phases for photovoltaics

Methylammonium lead iodide perovskite, CH₃NH₃PbI ₃, has attracted particular attention because of its fast increase in efficiency as solid-state solar cells. We performed first-principles calculations with the nonlocal van der Waals (vdW) correlation to investigate the crystal structures and electronic and optical properties of CH ₃NH₃PbI₃. The calculated results show that the distribution of methylammonium ions, which further changes the vdW interaction and hydrogen bonds of organic and inorganic matrixes, plays a vital role in both the geometry stability and the electronic structure. The vdW correlation is critical to provide appropriate descriptions of the interaction between the organic and the inorganic parts. The phase transformation from orthorhombic to tetragonal phase causes the decrease of the band gap and the red shift of the optical absorption coefficient.