Ultrafast carrier dynamics at organic donor–acceptor interfaces—a quantum-based assessment of the hopping model

Abstract

We investigate the charge transfer dynamics of photogenerated excitons at the donor-acceptor interface of an organic solar cell blend under the influence of molecular vibrations. This is examined using an effective Hamiltonian, parametrized by density functional theory calculations, to describe the full quantum behaviour of the relevant molecular orbitals, which are electronically coupled with each other and coupled to over one hundred vibrations (via Holstein coupling). This electron-phonon system is treated in a numerically quasi-exact fashion using the matrix-product-state ansatz. We provide insight into different mechanisms of charge separation and their relation to the electronic driving energy for the separation process. We find ultrafast electron transfer, which for small driving energy is dominated by kinetic processes and at larger driving energies by dissipative phonon emission connected to the prevalent vibration modes. Using this fully quantum mechanical model we perform a benchmark comparison to a recently developed semi-classical hopping approach, which treats the hopping and vibration time scales consistently. We find qualitatively and quantitatively good agreement between the results of the sophisticated matrix-product-state based quantum dynamics and the simple and fast time-consistent-hopping approach.

Charge transport in single polymer fiber transistors in the sub-100 nm regime: temperature dependence and Coulomb blockade

“…For similar polymers Barszcz et al [48] identified the C-C stretching vibration of thiophene rings at ≈0.173 eV and the in-phase C=C stretching of the DPP core at ≈0.2 eV. Similar results have been presented by Adil et al [49], Francis et al [50] and Dorfner et al [51]. If we assume coupling to the phonon modes as the origin for the excited states, these results compare very well with the electrically measured results in this work, which proves that excited states can be investigated also for OSCs via charge transport measurements.…”

Picosecond Charge-Transfer-State Dynamics in Wide Band Gap Polymer–Non-Fullerene Small-Molecule Blend Films Investigated via Transient Infrared Spectroscopy

“…In the literature, that process has been reported with a variety of time constants, both experimentally 10,22,24,25 and theoretically. 45 The CTS observed in our study forms after the transfer of one of the charges and might not be distinguishable in transient absorption spectroscopy in other spectral regions.…”

Vibronic coherences in light harvesting nanotubes: unravelling the role of dark states

“…† Models of this kind are common for the phenomenological description of vibrational coherent effects, electronic non-adiabatic couplings and vibrational relaxation/dephasing in various systems, [54][55][56][57] including electron transfer donor-acceptor systems 58 and organic interfaces. 59 Due to the enormous complexity and multidimensionality of the LHN system, we cannot give a microscopic underpinning or parameterization of the model Hamiltonian. The validity of this reduced description is verified a posteriori, since it gives a clear and insightful interpretation of the experimental signals.…”