This thesis focuses on the study of hybrid perovskites properties for the purposesof photovoltaic applications. During the almost four years PhD project that haslead to this thesis the record photovoltaic efficiency for this technology has in-creased from 10.9% to 22.1%. Such a significant pace of development can be com-pared with few other materials. It is for this reason that hybrid perovsites have at-tracted impressive research efforts. We approached the study of such unique ma-terials using computational ab-initio techniques, and in particular Density Func-tional Theory. We considered different materials, but most of the attention wasconcentrated on MAPI (CH 3 NH 3 PbI 3 ).The results are divided in three chapters, each exploring a different material prop-erty. The first chapter reports the electronic structure of the material bulk, sur-faces, and other electronic-related properties such as the rotation barrier for theorganic component and the Berry phase polarization.The second chapter focuses on the vibrational properties primary employing theharmonic approximation but also extends to the quasi-harmonic approximation.The outcome of these calculations permitted us to calculate theoretical IR and Ra-man spectra which are in good agreement with different experimental measure-ments. The quasi-harmonic approximation was used to calculate temperaturedependent properties, such as the Grüneisen parameter, the thermal dependenceof heat capacity and the thermal volumetric expansion.The third and last chapter reviews the thermodynamic properties of binary halidecompounds. The cobination of ab-initio calculations with the generalised quasi-chemical approximation has allowed to study the stability of mixed compositionperovskites. The results certified a set of stable structures that could stand at thebase of observed phenomena of photo-degradation of hybrid perovskite baseddevices.All three chapters have been written to understand the chemical and physicalbehaviour of hybrid perovskites and to extended and contribute to the under-standing of experimental work.
|Date of Award||12 Oct 2016|
|Sponsors||Destiny & CEC - Marie Curie|
|Supervisor||Aron Walsh (Supervisor) & Alison Walker (Supervisor)|
- Quantum theory
- solid state physics
- Materials science