Electronic structure and dynamics in the photovoltaic perovskite CH_3NH_3PbI_3
Abstract: I will talk about my recent work on the photovoltaic material methylammonium tri-iodide perovskite using density functional and excited-state calculations. This material has become a leading candidate for the next-generation, post-silicon solar-cell technology. Its current conversion efficiency stands at 20%, one of the highest among emerging photovoltaic materials. The lowest optically excited states are electron-hole bound states (excitons) of iodine-to-lead electron transfer character. I will also talk about real-time dynamics simulations using a system-bath Heisenberg equation-of-motion for the one-electron reduced density matrix to determine timescales of electronic relaxation in the conduction bands. In these simulations, an optical pump excites the dipole moment of a perovskite cluster. The dipole then decays due to the coupling of the cluster to the bath. The fourier transformed auto-correlation of the dipole gives information of the cluster's absorption spectrum which I then compare to the one found from GW+BSE and experiment. The picture that emerges is that electron relaxation down to the LUMO is on the scale of 100s of femto-seconds, whereas the relaxation from LUMO to HOMO is on the scale of tens of pico-seconds.
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