Research ArticleELECTRICAL CONDUCTORS

Long-range coupling of electron-hole pairs in spatially separated organic donor-acceptor layers

Science Advances  26 Feb 2016:
Vol. 2, no. 2, e1501470
DOI: 10.1126/sciadv.1501470

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Abstract

Understanding exciton behavior in organic semiconductor molecules is crucial for the development of organic semiconductor-based excitonic devices such as organic light-emitting diodes and organic solar cells, and the tightly bound electron-hole pair forming an exciton is normally assumed to be localized on an organic semiconducting molecule. We report the observation of long-range coupling of electron-hole pairs in spatially separated electron-donating and electron-accepting molecules across a 10-nanometers-thick spacer layer. We found that the exciton energy can be tuned over 100 megaelectron volts and the fraction of delayed fluorescence can be increased by adjusting the spacer-layer thickness. Furthermore, increasing the spacer-layer thickness produced an organic light-emitting diode with an electroluminescence efficiency nearly eight times higher than that of a device without a spacer layer. Our results demonstrate the first example of a long-range coupled charge-transfer state between electron-donating and electron-accepting molecules in a working device.

Keywords
  • Organic semiconductor
  • donor and acceptor molecules
  • electron-hole pairs

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