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Impact of quantized vibrations on the efficiency of interfacial charge separation in photovoltaic devices

Soumya Bera, Nicolas Gheeraert, Simone Fratini, Sergio Ciuchi, and Serge Florens
Phys. Rev. B 91, 041107(R) – Published 8 January 2015
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    Abstract

    We demonstrate that charge separation at donor-acceptor interfaces is a complex process that is controlled by the combined action of Coulomb binding for electron-hole pairs and partial relaxation due to quantized phonons. A joint electron-vibration quantum dynamical study reveals that high-energy vibrations sensitively tune the charge transfer probability as a function of time and injection energy, due to polaron formation. These results have bearings on the optimization of energy transfer both in organic and quantum dot photovoltaics, as well as in biological light harvesting complexes.

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    • Received 21 July 2014

    DOI:https://doi.org/10.1103/PhysRevB.91.041107

    ©2015 American Physical Society

    Authors & Affiliations

    Soumya Bera1, Nicolas Gheeraert1, Simone Fratini1, Sergio Ciuchi2, and Serge Florens1

    • 1Institut Néel, CNRS and Université Grenoble Alpes, F-38042 Grenoble, France
    • 2Dipartimento di Scienze Fisiche e Chimiche, Università dell'Aquila, CNISM and Istituto Sistemi Complessi CNR, via Vetoio, I-67010 Coppito-L'Aquila, Italy

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    Vol. 91, Iss. 4 — 15 January 2015

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    • Figure 1
      Figure 1

      Schematic diagram of the electron-vibration chain model to describe the dynamics at the donor-acceptor interface, Eq. (1). ε0 is the electronic energy after photoexcitation on the donor side, and the green curve represents the attractive Coulomb potential from the hole, which we suppose is localized at site l=0. The density of states of the noninteracting chain is shown on the right.

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    • Figure 2
      Figure 2

      Flow of electron density |Al(t)|2 at each site l as a function of time t (in units of 1/J≃20 fs), for an injection energy ε0=0.1 that is taken within the available band of delocalized states. Three different dynamics are performed: left panel, Coulomb confinement only (V=1,α2=0); middle panel, electron-phonon interaction only (V=0,α2=1); right panel, both interaction and confinement (V=1,α2=1). Only the latter case shows prominent localized states near the interface, which are, however, superposed with outgoing wave packets, giving a reduced but finite yield.

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    • Figure 3
      Figure 3

      Yield Y>30 as a function of incoming energy ε0, for various values of the electron-phonon coupling constant (the noninteracting case α2=0 is shown as a dashed line). The upper panel is the case without electron-hole binding (V=0), and the lower one has V=1. The combined effect of Coulomb binding and polaronic dressing of the carriers leads to a strong overall suppression of the yield.

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