Modeling Charge Carrier Dynamics at Perovskite/Charge Transport Material Interface Using Density Functional Theory and Redfield Theory
Landon Johnson1 and Dmitri Kilin2
1 Departments of Physics and Mathematics, North Dakota State University, Fargo, ND
2 Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND
Lead halide perovskite based solar cells (PSCs) have been a popular research topic over the last several years due to their rapidly increasing efficiencies and the ease of their fabrication. Titanium dioxides (TiO2) are frequently used as an electron transport material (ETM) in these solar cells to enhance the charge separation capabilities, thereby increasing the power conversion efficiency. Likewise, spiro-OMeTAD is often used as a hole transport material (HTM). We use density functional theory (DFT) to model the electronic structure of one such system via the HSE06 hybrid functional and by including spin-orbit coupling into the computations in the presence of an electric field. The system is composed of 252 atoms arranged periodically so that the perovskite forms a thin film while the TiO2 and spiro-OMeTAD are arranged as quantum dots and stand-alone molecules, respectively, on either side of the perovskite film. We also calculate non-adiabatic couplings between electronic states and nuclear motion “on-the-fly” during molecular dynamics to parameterize open system Redfield theory, which allows us to describe the excited state charge carrier dynamics with the main observable being the charge transfer rate. The goal is to describe the dynamics of photoexcited charge carriers driven by electron-phonon interactions at the interface between the perovskite and ETM/HTM in PSCs to further develop the understanding of the processes in these materials so that their chemical composition and morphology may be further improved. Specifically, we wish to establish a relationship between the interface structure and its properties, enable one direction of charge transfer while disabling the other, and control the rate of charge transfers. This will allow us to choose interface morphologies that will give higher efficiencies of photovoltaic devices. We also aim to determine the effect that an electric field has on the charge transfer characteristics. This knowledge can be used to effectively connect individual PSCs together, thereby creating more efficient solar panel architectures.
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