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Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control


Infrared light-emitting diodes are currently fabricated from direct-gap semiconductors using epitaxy, which makes them expensive and difficult to integrate with other materials. Light-emitting diodes based on colloidal semiconductor quantum dots, on the other hand, can be solution-processed at low cost, and can be directly integrated with silicon1. However, so far, exciton dissociation and recombination have not been well controlled in these devices, and this has limited their performance2,3,4,5,6,7,8. Here, by tuning the distance between adjacent PbS quantum dots, we fabricate thin-film quantum-dot light-emitting diodes that operate at infrared wavelengths with radiances (6.4 W sr−1 m−2) eight times higher and external quantum efficiencies (2.0%) two times higher than the highest values previously reported. The distance between adjacent dots is tuned over a range of 1.3 nm by varying the lengths of the linker molecules from three to eight CH2 groups, which allows us to achieve the optimum balance between charge injection and radiative exciton recombination. The electroluminescent powers of the best devices are comparable to those produced by commercial InGaAsP light-emitting diodes. By varying the size of the quantum dots, we can tune the emission wavelengths between 800 and 1,850 nm.

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Figure 1: Physical and electronic structure of the LEDs.
Figure 2: Relationship between LED performance and inter-dot distance.
Figure 3: Current density–voltage characteristic of a device made of MOA-capped quantum dots with diameters of 4.5 nm.
Figure 4: Emission spectra and infrared image of LEDs.


  1. Cho, K. et al. High-performance crosslinked colloidal quantum-dot light-emitting diodes. Nature Photon. 3, 341–345 (2009).

    CAS  Article  Google Scholar 

  2. Colvin, V. L., Schlamp, M. C. & Alivisatos, A. P. Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer. Nature 370, 354–357 (1994).

    CAS  Article  Google Scholar 

  3. Coe, S., Woo, W., Bawendi, M. & Bulović, V. Electroluminescence from single monolayers of nanocrystals in molecular organic devices. Nature 420, 800–803 (2002).

    CAS  Article  Google Scholar 

  4. Tessler, N., Medvedev, V., Kazes, M., Kan, S. & Banin, U. Efficient near-infrared polymer nanocrystal light-emitting diodes. Science 295, 1506–1508 (2002).

    Article  Google Scholar 

  5. Steckel, J. S., Coe-Sullivan, S., Bulović, V. & Bawendi, M. G. 1.3 µm to 1.55 µm tunable electroluminescence from PbSe quantum dots embedded within an organic device. Adv. Mater. 15, 1862–1866 (2003).

    CAS  Article  Google Scholar 

  6. Caruge, J. M., Halpert, J. E., Wood, V., Bulović, V. & Bawendi, M. G. Colloidal quantum-dot light-emitting diodes with metal-oxide charge transport layers. Nature Photon. 2, 247–250 (2008).

    CAS  Article  Google Scholar 

  7. Bourdakos, K. N., Dissanayake, D. M. N. M., Lutz, T., Silva, S. R. P. & Curry, R. J. Highly efficient near-infrared hybrid organic–inorganic nanocrystal electroluminescence device. Appl. Phys. Lett. 92, 153311 (2008).

    Article  Google Scholar 

  8. Konstantatos, G., Huang, C., Levina, L., Lu, Z. & Sargent, E. H. Efficient infrared electroluminescent devices using solution-processed colloidal quantum dots. Adv. Funct. Mater. 15, 1865–1869 (2005).

    CAS  Article  Google Scholar 

  9. Wise, F. W. Lead salt quantum dots: the limit of strong quantum confinement. Acc. Chem. Res. 33, 773–780 (2000).

    CAS  Article  Google Scholar 

  10. Choi, J. J. et al. PbSe nanocrystal excitonic solar cells. Nano Lett. 9, 3749–3755 (2009).

    CAS  Article  Google Scholar 

  11. Konstantatos, G. et al. Ultrasensitive solution-cast quantum dot photodetectors. Nature 442, 180–183 (2006).

    CAS  Article  Google Scholar 

  12. Huang, H., Dorn, A., Nair, G. P., Bulović, V. & Bawendi, M. G. Bias-induced photoluminescence quenching of single colloidal quantum dots embedded in organic semiconductors. Nano Lett. 7, 3781–3786 (2007).

    CAS  Article  Google Scholar 

  13. Choi, J. J. et al. Photogenerated exciton dissociation in highly coupled lead salt nanocrystal assemblies. Nano Lett. 10, 1805–1811 (2010).

    CAS  Article  Google Scholar 

  14. Hyun, B. R. et al. Electron injection from colloidal PbS quantum dots into titanium dioxide nanoparticles. ACS Nano 2, 2206–2212 (2008).

    CAS  Article  Google Scholar 

  15. Verbakel, F., Meskers, S. C. J. & Janssen, R. A. J. Electronic memory effects in diodes of zinc oxide nanoparticles in a matrix of polystyrene or poly(3-hexylthiophene). J. Appl. Phys. 102, 083701 (2007).

    Article  Google Scholar 

  16. Kepler, R. G. et al. Electron and hole mobility in tris(8-hydroxyquinolinolato-N1,O8) aluminum. Appl. Phys. Lett. 66, 3618–3620 (1995).

    CAS  Article  Google Scholar 

  17. Shimizu, K. T., Woo, W. K., Fisher, B. R., Eisler, H. J. & Bawendi, M. G. Surface-enhanced emission from single semiconductor nanocrystals. Phys. Rev. Lett. 89, 117401 (2002).

    CAS  Article  Google Scholar 

  18. Barkhouse, D. A., Kramer, I. J., Wang, X. & Sargent, E. H. Dead zones in colloidal quantum dot photovoltaics: evidence and implications. Opt. Express 18, A451–A457 (2010).

    CAS  Article  Google Scholar 

  19. Murray, C. B., Kagan, C. R. & Bawendi, M. G. Synthesis and characterization of monodisperse nanocrystals and close-packed nanocrystal assemblies. Annu. Rev. Mater. Sci. 30, 545–610 (2000).

    CAS  Article  Google Scholar 

  20. Hines, M. A. & Scholes, G. D. Colloidal PbS nanocrystals with size-tunable near-infrared emission: observation of post-synthesis self-narrowing of the particle size distribution. Adv. Mater. 15, 1844–1849 (2003).

    CAS  Article  Google Scholar 

  21. Semonin, O. E. et al. Absolute photoluminescence quantum yields of IR-26 dye, PbS, and PbSe quantum dots. J. Phys. Chem. Lett. 1, 2445–2450 (2010).

    CAS  Article  Google Scholar 

  22. Malliaras, G. G., Salem, J. R., Brock, P. J. & Scott, C. Electrical characteristics and efficiency of single-layer organic light-emitting diodes. Phys. Rev. B 58, R13411–R13414 (1998).

    CAS  Article  Google Scholar 

  23. Malliaras, G. G. & Scott, J. C. The roles of injection and mobility in organic light emitting diodes. J. Appl. Phys. 83, 5399–5403 (1998).

    CAS  Article  Google Scholar 

  24. Pattantyus-Abraham, A. G. et al. Depleted-heterojunction colloidal quantum dot solar cells. ACS Nano 4, 3374–3380 (2010).

    CAS  Article  Google Scholar 

  25. Talapin, D. V. & Murray, C. B. PbSe nanocrystal solids for n- and p-channel thin film field-effect transistors. Science 310, 86–89 (2005).

    CAS  Article  Google Scholar 

  26. Law, M. et al. Structural, optical, and electrical properties of PbSe nanocrystal solids treated thermally or with simple amines. J. Am. Chem. Soc. 130, 5974–5985 (2008).

    CAS  Article  Google Scholar 

  27. Greenham, N. C., Friend, R. H. & Bradley, D. D. C. Angular dependence of the emission from a conjugated polymer light-emitting diode: implications for efficiency calculations. Adv. Mater. 6, 491–494 (1994).

    CAS  Article  Google Scholar 

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This material is based on work supported by the National Science Foundation (NSF, grant no. EEC-0646547) and by the New York State Foundation for Science, Technology and Innovation (NYSTAR). J.J.C. and D.S. acknowledge support from the Cornell Center for Materials Research with funding from IGERT: a Graduate Traineeship in Nanoscale Control of Surfaces and Interfaces (DGE-0654193) of the NSF. This publication is based on work supported in part by an award (no. KUS-C1-018-02) made by King Abdullah University of Science and Technology (KAUST). GISAXS measurements were conducted at Cornell High Energy Synchrotron Source (CHESS) and the authors thank D.-M. Smilgies for calibration of the beam line set-up.

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L.S. and J.J.C. conceived and designed the experiments. L.S. and D.S. performed device characterization and optical measurements. J.J.C. synthesized the materials, fabricated the devices, and performed GISAXS and optical measurements. A.C.B. calculated the energy levels of the quantum dots. L.S. and F.W.W. co-wrote the paper. F.W.W., T.H. and G.G.M. (now at Ecole Nationale Supérieure des Mines, France) supervised the project. All authors discussed the work, commented on the manuscript and contributed to revision of the manuscript.

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Correspondence to Liangfeng Sun or Frank W. Wise.

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The authors declare no competing financial interests.

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Sun, L., Choi, J., Stachnik, D. et al. Bright infrared quantum-dot light-emitting diodes through inter-dot spacing control. Nature Nanotech 7, 369–373 (2012).

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