Ab Initio Study of Charge Separation Dynamics and Pump–Probe Spectroscopy in the P3HT/PCBM Blend

19 April 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


We develop a computational method for excited-state dynamics and time-resolved spectroscopy signals in molecular aggregates, on the basis of ab initio excited-state calculations. As an application, we consider the charge separation dynamics and pump--probe spectroscopy in the amorphous P3HT/PCBM blend. To simulate quantum dynamics and time-resolved spectroscopy, the model Hamiltonian for single-excitation and double-excitation manifolds was derived on the basis of fragment-based excited-state calculations within the GW approximation and the Bethe--Salpeter equation. After elucidating the energetics of the electron--hole separation and examining linear absorption spectrum, we investigated the quantum dynamics of exciton and charge carriers in comparison with the pump--probe transient absorption spectra. In particular, we introduced the pump--probe excited-state absorption (ESA) anisotropy as a spectroscopic signature of charge carrier dynamics after exciton dissociation. We found that the charge separation dynamics can be probed by the pump--probe ESA anisotropy dynamics after charge-transfer excitations. The present study provides the fundamental information for understanding the experimental spectroscopy signals, by elucidating the relationship between the excited states, the exciton and charge carrier dynamics, and the time-resolved spectroscopy.


Organic Solar Cells
Bethe-Salpeter Equation
Fragment Molecular Orbital Method
Charge Transfer

Supplementary materials

Supplementary Information
Excited states of P3HT tetramer cation, terms contributing to the four-wave mixing signals, details for quantum dynamics and spectroscopy simulations, and wavefunction properties.


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