Abstract
It has long been a puzzle on what drives charge separation in artificial polymeric solar cells as a consensus has yet to emerge among rivaling theories based upon electronic localization and delocalization pictures. Here we propose an alternative using the two-bath spin-boson model with simultaneous diagonal and off-diagonal coupling: the critical phase, which is born out of the competition of the two coupling types, and is neither localized nor delocalized. The decoherence-free feature of the critical phase also helps explain sustained coherence of the charge-transfer state. Exploiting Hamiltonian symmetries in an enhanced algorithm of density-matrix renormalization group, we map out boundaries of the critical phase to a precision previously unattainable, and determine the bath spectral densities inducive to the existence of the charge-transfer state.
Highlights
Recombination from the CT state to the exciton, while dominating off-diagonal coupling converts the CT state to the CS state[2]
Inspired by recent discovery on the novelty of the CT state[8], we report in this paper our findings on the two-bath spin-boson model (SBM) (TBSBM) after taking into account[42] simultaneous diagonal and off-diagonal coupling
We have studied critical phase of the TBSBM in both the deep and shallow sub-Ohmic regimes
Summary
Recombination from the CT state to the exciton, while dominating off-diagonal coupling converts the CT state to the CS state[2]. From this perspective, in either scenario, the CT state seems to be an short-lived transient state in the charge separation process. More interesting to consider is the Munn-Silbey approach to simultaneous diagonal and off-diagonal coupling in molecular crystals[18,19,41], which states that the diffusion coefficient of charge carriers in molecular crystals is dominated by the competition between the two forms of vibronic coupling. We focus on results from a critical phase born out of the competition between diagonal and off-diagonal coupling, setting up a benchmarking microscopic model for the study of the charge separation process in PSCs
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