Silicon is one of the most common solar cell materials due to its availability, ideal band gap, and high efficiency. However, it also needs to be processed onto glass substrates, which is a very delicate and costly procedure. Research has turned its attention towards organic materials, which can be processed relatively cheaply onto plastic substrates but are not nearly as efficient as silicon. One of the key issues behind the low efficiency of organic materials is that charge recombination is highly likely and usually occurs quickly. However, photosynthesis may help to elucidate a method to enhance organic materials’ efficiencies. The Fenna-Matthews-Olson complex in green sulfur bacteria transports charge between the chlorosome and the photosynthetic reaction center and utilizes quantum coherence during the electron energy transfer. The coherence has been shown to increase efficiency by offsetting radiative recombination and allows the complex to determine the most efficient path. Understanding the quantum dynamics behind the charge transport process will help extrapolate a model that can be applied to organic solar cell materials. To model the dynamics of the electron transport process, we are using a combination of the Ehrenfest method, which has already been tested on the two-state Spin-Boson model, and Multi-Configuration Time-Dependent Hartree for a seven-state system. However, one of the major drawbacks of quantum calculations is the high computational cost. To circumvent this, we plan to implement the Generalized Quantum Master Equation. The Nakajima-Zwanzig Generalized Quantum Master Equation determines the quantum dynamics of a coupled system and bath where the bath effects are determined by the memory kernel. The system-dependent bath correlation functions can be calculated via the linearized semiclassical method. When applied to the Spin-Boson model and compared against the direct linearized semiclassical method, weak coupling, and exact data, LSC-GQME is an almost perfect fit to the exact data. We expect that when GQME is applied to a seven-state system it will yield a close fit to previously measured data.

Modeling the quantum dynamics behind charge transport in photosynthetic reaction centers beyond the Spin-Boson model

2019 Spring National Meeting

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