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Browsing School of Physics (ETDs) by Keyword "ab initio"

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    Solar cell simulation using ab initio methods
    (University of the Witwatersrand, Johannesburg, 2024) Zdravkovi´c, Milica; Quand, Alexander; Warmbier, Robert
    Solar cells are a great source of renewable energy, but they are yet to reach their thermodynamic efficiency limits. Common commercial solar cells run at approximately 20% power conversion efficiency, and almost all efficiency loss comes from thermalisation. Ab initio simulations can reduce the need for physical experiments to quantify these losses while also providing insights into the quantum mechanical properties of materials. Note that density functional theory reformulates the expression for the ground state energy of a many particle system such that it is a functional of the electron density, thereby allowing the electronic energy to be solved for numerically. But the underlying mechanism behind thermalisation is the electron-phonon interaction. Using the theory of Green’s functions, the electron-phonon interaction self-energy and charge-carrier life times can be calculated. A method of approximating the charge-carrier lifetimes using the hydrostatic deformation potential interaction, which is only valid for longitudinal acoustic phonons, is presented. Deformation potentials of -10.125eV for Silicon and 18.663eV for Gallium Arsenide, commonly used solar cell materials, are calculated in good agreement with literature. Furthermore, the electron-phonon interaction life- times were calculated to be in the order of 2.0 × 10−15s for Si and 4.0 × 10−16s for GaAs, which could have indications that the optimal thickness of a GaAs absorption layer is much thinner than for Si. Thus the deformation potential method provides a satisfactory approximation for the electron-phonon quasiparticle lifetimes based on ab initio methods