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arXiv · 1609.01501

Origin of space-separated charges in photoexcited organic heterojunctions on ultrafast time scales

Veljko Janković·Nenad Vukmirović
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Abstract

We present a detailed investigation of ultrafast (subpicosecond) exciton dynamics in the lattice model of a donor/acceptor heterojunction. Exciton generation by means of a photoexcitation, exciton dissociation, and further charge separation are treated on equal footing. The experimentally observed presence of space-separated charges at $\lesssim 100$ fs after the photoexcitation is usually attributed to ultrafast transitions from excitons in the donor to charge transfer and charge separated states. Here, we show, however, that the space-separated charges appearing on $\lesssim 100$-fs time scales are predominantly directly optically generated. Our theoretical insights into the ultrafast pump-probe spectroscopy challenge usual interpretations of pump-probe spectra in terms of ultrafast population transfer from donor excitons to space-separated charges.

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Veljko Janković, Nenad Vukmirović. 2017-02-22. Origin of space-separated charges in photoexcited organic heterojunctions on ultrafast time scales. https://doi.org/10.1103/physrevb.95.075308

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