Journal
NANO LETTERS
Volume 18, Issue 2, Pages 785-792Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b03995
Keywords
Charge transfer; real-time simulations; nonequilibrium Green functions; donor-acceptor complex; ultrafast dynamics
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Funding
- Swedish Research Council (VR)
- European Union [676598, 654360]
- MIUR FIRB [RBFR12SW0J]
- EC through the RISE Co-ExAN [GA644076]
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We use the nonequilibrium Green function (NEGF) method to perform real-time simulations of the ultrafast electron dynamics of photoexcited donor-C-60 complexes modeled by a Pariser-Parr-Pople Hamiltonian. The NEGF results are compared to mean-field Hartree-Fock (HF) calculations to disentangle the role of correlations. Initial benchmarking against numerically highly accurate time-dependent density matrix renormalization group calculations verifies the accuracy of NEGF. We then find that charge-transfer (CT) excitons partially decay into charge separated (CS) states if dynamical nonlocal correlation corrections are included. This CS process occurs in similar to 10 fs after photoexcitation. In contrast, the probability of exciton recombination is almost 100% in HF simulations. These results are largely unaffected by nuclear vibrations; the latter become however essential whenever level misalignment hinders the CT process. The robust nature of our findings indicates that ultrafast CS driven by correlation-induced decoherence may occur in many organic nanoscale systems, but it will only be correctly predicted by theoretical treatments that include time-nonlocal correlations.
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