Quantum Dynamics Simulations of Organic Semiconductors after Photoexcitations using Tensor Networks

Sam Mardazad¹, Yihe Xu², Xuexiao Yang², Martin Grundner¹, Ulrich Schollwöck¹, Haibo Ma², Sebastian Paeckel^1*

¹Arnold Sommerfeld Center of Theoretical Physics, Department of Physics, University of Munich, Munich, Germany
²School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China

* Presenter:Sebastian Paeckel, email:sebastian.paeckel@physik.uni-muenchen.de

Organic semiconductors potentially can yield solar power conversion efficiencies beyond the Shockley-Queisser limit of solid-state single pn-junction based solar cells, by generating more than only one excited electron per absorbed photon. Typically, these processes are based on the spin allowed down-conversion of highly excited molecular states, assisted by the coupling to a large set of molecular vibrational modes, which is called singlet fission. Here, being able to simulate the complex interplay between electronic and vibronic molecular modes in an out-of-equilibrium situation is crucial to understand and enhance the probability of this down-conversion to occur. In my presentation, I am going to talk about recently developed tensor network based methods to tackle this challenging problem. Exploiting a new state representation in an enlarged Hilbert space, the computational costs can be reduced by more than an order of magnitude, allowing the simulation of a realistic number of vibrational modes and phonons in an excited molecule. Using this advanced numerical technique, we were able to study the full quantum dynamics in a realistic setup, obtaining excellent agreement with actual experimental data and, furthermore, are able to make predictions on how to alter experimental and molecular parameter to increase singlet fission.

Keywords: Singlet Fission, Organic Semiconductor, Tensor Networks, Out-of-Equilibrium, Phonons