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The Optical and Electronic Properties of Organic-Inorganic Hybrid Perovskites

Student thesis: Doctoral ThesisDoctor of Philosophy

The primary focus of this thesis is the study of a novel family of materials known as organicinorganic hybrid Perovskites (OIHP), which have recently demonstrated to possess remarkable photovoltaic efficiency. The fundamental properties of these materials related to photovoltaic (PV) applications are studied to characterise electronic and optical behaviours. An all-electron implementation of the Quasi-particle Self-consistent GW (QSGW) is used to perform first principles calculations. The quasi-particle energy bands are analysed for a number of Perovskites, to identify trends and characteristics within this family of materials, and to understand the dielectric response. The dielectric function and refractive index were studied for 4 OIHP and compared to experimental work carried out collaboratively with Leguy et al. [1]. It is found that the relativistic effects are extremely important in characterisation of these materials. The presence of strong spin-orbit interaction combined with significant internal electric fields yields anomalously large Rashba splitting of both valence and conduction states near the band edges. This significantly perturbs the electronic and optical properties of these materials. Such effects have not been previously investigated in the context of photovoltaic materials. The effect of the Rashba splitting on the radiative recombination lifetime of charge carriers is investigated. A model for reciprocal space trapping mechanism of carriers was developed and implemented within the Questaal package. The slightly indirect gap induced by Rashba splitting results in a strongly suppressed photoluminescence when compared to conventional III-V direct-gap semiconductors with an otherwise approximately similar band structure. Such suppression of the radiative recombination enhances the diffusion length and can significantly increase the power conversion efficiency of a solar cell.
Original languageEnglish
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Award date2018

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