Exciton dynamics of C60-based single-photon emitters explored by Hanbury Brown-Twiss scanning tunnelling microscopy.

P Merino,A Rosławska,C Große,K Kern,K Kuhnke

doi:10.1038/ncomms9461

Abstract

Exciton creation and annihilation by charges are crucial processes for technologies relying on charge-exciton-photon conversion. Improvement of organic light sources or dye-sensitized solar cells requires methods to address exciton dynamics at the molecular scale. Near-field techniques have been instrumental for this purpose; however, characterizing exciton recombination with molecular resolution remained a challenge. Here, we study exciton dynamics by using scanning tunnelling microscopy to inject current with sub-molecular precision and Hanbury Brown–Twiss interferometry to measure photon correlations in the far-field electroluminescence. Controlled injection allows us to generate excitons in solid C60 and let them interact with charges during their lifetime. We demonstrate electrically driven single-photon emission from localized structural defects and determine exciton lifetimes in the picosecond range. Monitoring lifetime shortening and luminescence saturation for increasing carrier injection rates provides access to charge-exciton annihilation dynamics. Our approach introduces a unique way to study single quasi-particle dynamics on the ultimate molecular scale.

Highlights

Exciton creation and annihilation by charges are crucial processes for technologies relying on charge-exciton-photon conversion
Addressing recombination with sub-wavelength resolution has been established by using scanning optical near-field probes[14,18,19,20], stimulated emission depletion microscopy[21] and, prominently, by electroluminescence from organic molecules in scanning tunnelling microscopy (STM)[22,23]
We demonstrate a solution to this problem by using STM to inject current with sub-molecular precision and a Hanbury Brown–Twiss (HBT) interferometer to confirm SP emission in electroluminescence

Summary

Introduction

Exciton creation and annihilation by charges are crucial processes for technologies relying on charge-exciton-photon conversion. Measurements of photon–photon time correlations on such emitters can be employed to prove their sub-Poissonian photon statistics for which short delays between successive emission events are less likely to occur than longer ones (photon ‘antibunching’). Addressing recombination with sub-wavelength resolution has been established by using scanning optical near-field probes[14,18,19,20], stimulated emission depletion microscopy[21] and, prominently, by electroluminescence from organic molecules in scanning tunnelling microscopy (STM)[22,23].

Results

Conclusion