Physics / Physique - Master's Theses

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Browsing Physics / Physique - Master's Theses by Author "Morningstar, Brendan"

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    First principle study of the electronic structure of semiconductors for photovoltaic applications: organic-inorganic perovskites
    (2018-08-18) Morningstar, Brendan
    The ill effects of climate change affect all trends, and the steps taken in the drive to reduce global emissions will reverberate for thousands of years. It is among the most significant and urgent problems we face, and so it is immensely important to call upon existing and near future technologies for generating clean electricity. For now, the most talked-about renewable energy source is solar. It is a massive resource by any standard and it has the potential to play an essential role in decreasing the dependency on crude oil and reducing fossil fuel emissions. Today, the best-performing perovskite cell has reached a power conversion efficiency of 22.1%. This unprecedented rise in efficiency for a photovoltaic technology suggests a sunny outlook, but before a large-scale deployment of the technology, there are still some real questions that must be addressed. The best performing perovskite cells contain lead, which is very toxic and damaging to the environment, and are unstable in humid conditions. Also, the fundamental working of these materials is still largely unknown. The technological base of photovoltaics is becoming progressively dependent on complicated materials, and so it is important to systematically investigate the nature of the electronic structure. In the present work, the electronic structure of five perovskite compounds, MAPbBr3, CsPbX3 (X=Cl, Br, I) and RbPbI3, are systematically studied from first principles using the all-electron, full potential, linearized augmented plane wave ((L)APW) + local orbitals (lo) method as implemented in the WIEN2k code. It is noted that: (i) the band gap of ABX3 increases when A changes from MA to Cs; (ii) as X changes from Br to Cl to I, the band gap increases; and (iii) as A changes from Cs to Rb, the band gap mostly remains the same.