Vibrational properties of hybrid halide perovskite for solar cells applications

The outstanding electronic properties of methylammonium lead iodide make it attractive for a wide range of applications, particularly in the photovoltaic field. CH3NH3PbI3 as well as other closely related hybrid perovskites all display band gaps from 1.1 to 2.1 eV in the visible light range, favorable for photovoltaic applications. This class of materials also exhibits a large absorption coefficient, low dual electron and hole effective masses and high carrier mobilities. The aim of this work is the understanding of the vibrational properties of the stable phase of the material at low-temperature and the extraction of the link with the outstand- ing transport properties. The structural, electronic, vibrational and dielectric properties of this material are theoretically determined by an ab initio calculation based on the Density Functional Perturbation Theory and are compared as much as possible with experimental results found in the literature. Several properties of this material are characterized, including the lattice parameters of the relaxed structure, the electronic band gap, the Born effective charges, the dielectric tensors and the infrared intensities. The agreement with the experimental results varies depending on the studied property. Different cases will be distinguished according to the inclusion or not of several physico- chemical phenomena involved in such a material. Among them, the spin-orbit coupling and the van der Waals interactions whose role is still not enough implemented from a theoretical point of view. This study confirms the importance of taking these corrections into account in order to get more realistic material properties.