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Electroluminescence from single monolayers of nanocrystals in molecular organic devices

Abstract

The integration of organic and inorganic materials at the nanometre scale into hybrid optoelectronic structures enables active devices1,2,3 that combine the diversity of organic materials with the high-performance electronic and optical properties of inorganic nanocrystals4. The optimization of such hybrid devices ultimately depends upon the precise positioning of the functionally distinct materials. Previous studies5,6 have already emphasized that this is a challenge, owing to the lack of well-developed nanometre-scale fabrication techniques. Here we demonstrate a hybrid light-emitting diode (LED) that combines the ease of processability of organic materials with the narrow-band, efficient luminescence of colloidal quantum dots7 (QDs). To isolate the luminescence processes from charge conduction, we fabricate a quantum-dot LED (QD-LED) that contains only a single monolayer of QDs, sandwiched between two organic thin films. This is achieved by a method that uses material phase segregation between the QD aliphatic capping groups and the aromatic organic materials. In our devices, where QDs function exclusively as lumophores, we observe a 25-fold improvement in luminescence efficiency (1.6 cd A-1 at 2,000 cd m-2) over the best previous QD-LED results5. The reproducibility and precision of our phase-segregation approach suggests that this technique could be widely applicable to the fabrication of other hybrid organic/inorganic devices.

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Figure 1: Electroluminescence spectra and structures for two QD-LEDs, devices I and II.
Figure 2: AFM images showing the surface morphology of various organic/QD films.
Figure 3: External quantum efficiency versus current density for the two devices shown in Fig. 1.
Figure 4: Proposed energy level diagram of device I.

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Acknowledgements

We thank D. Mascaro and E. Shaw for assistance in acquiring AFM images. This work was supported in part by the NSF-MRSEC programme, DMR, and Universal Display Corporation; it made use of MRSEC shared facilities supported by the National Science Foundation.

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Correspondence to Vladimir Bulović.

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Coe, S., Woo, WK., Bawendi, M. et al. Electroluminescence from single monolayers of nanocrystals in molecular organic devices. Nature 420, 800–803 (2002). https://doi.org/10.1038/nature01217

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