TY - THES

T1 - An open quantum system approach to deal with correlated photovoltaic systems

AU - Werner, Daniel

N1 - no embargo

PY - 2021

Y1 - 2021

N2 - In this master thesis, our goal is to simulate a simplified photovoltaic setup, and to study the average current as a function of the frequency of a monochromatic light source. Physically, we may imagine our system as a semiconductor, which is influenced by the periodic electric field, connected to two metallic leads, where the energy of the left lead is smaller than the one of the right lead and application of electron-magnetic radiation provides the energy to move electrons from the left to the right lead, allowing for energy harvesting. In two of our setups we have a band gap due to a specific structure and parameter choice. For the third setup the gap is caused by electron-electron interaction, which is the case we are most interested in.The energy of the left lead, and the lower band of the semiconductor are chosen to overlap, as well as the energy of the right lead and the upper band gap of the semiconductor. Therefore, electrons coming in from the left can easily find a state in the lower band of the central region they can occupy.To simulate this open quantum system, the Lindblad equation has been used, which means we must assume that the influence of the system on the environment is negligible, compared to the reveres process. If we want to take into account electron-electron interaction, we must perform the exact diagonalization of the many body density-matrix to solve this equation, which is strongly limiting the system size. For the non-interacting case, we can use the equations of motion, which allow for larger setups.The shape of the average current as a function of frequency, reflected the respective band gaps quite well in most cases. One of our main findings is, that we found maxima in the average cur-rent plots, that lie at a fraction (1/2, 1/3) of the gap size, and increase with intensity, which are interpreted in terms of excitations due to the absorption of two or more photons.

AB - In this master thesis, our goal is to simulate a simplified photovoltaic setup, and to study the average current as a function of the frequency of a monochromatic light source. Physically, we may imagine our system as a semiconductor, which is influenced by the periodic electric field, connected to two metallic leads, where the energy of the left lead is smaller than the one of the right lead and application of electron-magnetic radiation provides the energy to move electrons from the left to the right lead, allowing for energy harvesting. In two of our setups we have a band gap due to a specific structure and parameter choice. For the third setup the gap is caused by electron-electron interaction, which is the case we are most interested in.The energy of the left lead, and the lower band of the semiconductor are chosen to overlap, as well as the energy of the right lead and the upper band gap of the semiconductor. Therefore, electrons coming in from the left can easily find a state in the lower band of the central region they can occupy.To simulate this open quantum system, the Lindblad equation has been used, which means we must assume that the influence of the system on the environment is negligible, compared to the reveres process. If we want to take into account electron-electron interaction, we must perform the exact diagonalization of the many body density-matrix to solve this equation, which is strongly limiting the system size. For the non-interacting case, we can use the equations of motion, which allow for larger setups.The shape of the average current as a function of frequency, reflected the respective band gaps quite well in most cases. One of our main findings is, that we found maxima in the average cur-rent plots, that lie at a fraction (1/2, 1/3) of the gap size, and increase with intensity, which are interpreted in terms of excitations due to the absorption of two or more photons.

KW - photovoltaic

KW - quantum mechanics

KW - correlated systems

KW - band gap

KW - Photovoltaik

KW - Quantenmechanik

KW - korrelierte Systeme

KW - Bandlücke

M3 - Master's Thesis

ER -