Electroluminescent Characteristics of CdSe Colloidal Quantum Dots

doi:10.3724/SP.J.1077.2012.12027

Abstract

Abstract: Electroluminescent (EL) devices with an ITO/ZnS/CdSe/ZnS/Al structure were fabricated using chemically synthesized colloidal CdSe quantum dots (QDs) as active layer. The size of the CdSe QDs is about 4.3 nm measured by a transmission electron microscope. Scanning electron microscope characterization shows smooth surfaces of ZnS layers and Al electrodes. CdSe (111) and ZnS (111) diffraction peaks are observed in the X-ray diffraction patterns, verifying the incorporation of CdSe QDs and ZnS insulator materials in the devices. Room temperature photoluminescence (PL) spectra reveal that the CdSe QDs’ emission peak is located at 614 nm. EL measurements at room temperature show a broad emission band ranging from 450 nm to 850 nm with a peak wavelength located at about 800 nm. Finally, the light emitting mechanism for the EL devices is proposed and the discrepancy between PL and EL spectra is interpreted.

Key words: CdSe, quantum dots, electroluminescence, photoluminescence

CLC Number:

O443

LOU Teng-Gang, HU Lian, WU Dong-Kai, DU Ling-Xiao, CAI Chun-Feng, SI Jian-Xiao, WU Hui-Zhen. Electroluminescent Characteristics of CdSe Colloidal Quantum Dots[J]. Journal of Inorganic Materials, 2012, 27(11): 1211-1215.

References

[1] Coe S, Woo W K, Bawendi M, et al. Electroluminescence from single monolayers of nanocrystals in molecular organic devices. Nature, 2002, 420(6917): 800–803.

[2] Leventis H C, King S P, Sudlow A, et al. Nanostructured hybrid polymer-inorganic solar cell active layers formed by controllable in situ growth of semiconducting sulfide networks. Nano Lett., 2010, 10(4): 1253–1258.

[3] Yoffe A D. Semiconductor quantum dots and related systems: electronic, optical, luminescence and related properties of low dimensional systems. Adv. Phys., 2001, 50(1): 1–208.

[4] Li F S, Cho S H, Son D I, et al. UV photovoltaic cells based on conjugated ZnO quantum dot/multiwalled carbon nanotube heterostructures. Appl. Phys. Lett., 2009, 94(11): 111906–1–3.

[5] Li Y Q, Rizzo A, Mazzeo M, et al. White organic light-emitting devices with CdSe/ZnS quantum dots as a red emitter. J. Appl. Phys., 2005, 97(11): 113501–1–4.

[6] Anikeeva P O, Halpert J E, Bawendi M G, et al. Quantum dot light-emitting devices with electroluminescence tunable over the entire visible spectrum. Nano Lett., 2009, 9(7): 2532–2536.

[7] Li F S, Guo T L, Kim T. Charge trapping in hybrid electroluminescence device containing CdSe/ZnS quantum dots embedded in a conducting poly(N-vinylcarbozole) layer. Appl. Phys. Lett., 2010, 97(6): 062104–1–3.

[8] Caruge J M, Halpert J E, Wood V, et al. Colloidal quantum-dot light-emitting diodes with metal-oxide charge transport layers. Nature Photonics, 2008, 2(4): 247–250.

[9] Arians R, Kummell T, Bacher G, et al. Room temperature emission from CdSe/ZnSSe/MgS single quantum dots. Appl. Phys. Lett., 2007, 90(10): 101114–1–3.

[10] Cheng G, Mazzeo M, Rizzo A, et al. White light-emitting devices based on the combined emission from red CdSe/ZnS quantum dots, green phosphorescent, and blue fluorescent organic molecules. Appl. Phys. Lett., 2009, 94(24): 243506–1–3.

[11] Wang X B, Li W W, Sun K. Stable efficient CdSe/CdS/ZnS core/multi-shell nanophosphors fabricated through a phosphine- free route for white light-emitting-diodes with high color rendering properties. J. Mater. Chem., 2011, 21(24): 8558–8565.

[12] Du L X, Hu L, Zhang B P, et al. Photoluminescence enhancement of colloidal quantum dots embedded in a microcavity. Acta Phys. Sin., 2011, 60(11): 117803–1–5.

[13] Hu L, Wu H Z, Du L X, et al. The effect of annealing and photoactivation on the optical transitions of band–band and surface trap states of colloidal quantum dots in PMMA. Nanotech., 2011, 22(12): 125202–1–6.

[14] Wu D G, Kordesch M E, Van Patten P G. A new class of capping ligands for CdSe nanocrystal synthesis. Chem. Mater., 2005, 17(25): 6436–6441.

[15] Benamar E, Rami M, Messaoudi C, et al. Structural, optical and electrical properties of indium tin oxide thin films prepared by spray pyrolysis. Solar Energy Materials & Solar Cells, 1999, 56(2): 125–139.

[16] Luan W L, Yang H W, Tu S T, et al. Open-to-air synthesis of monodisperse CdSe nanocrystals via microfluidic reaction and its kinetics. Nanotech., 2007, 18(17): 175603–1–6.

[17] Qadri S B, Skelton E F, Hsu D, et al. Size-induced transition-temperature reduction in nanoparticles of ZnS. Physical Review B, 1999, 60(13): 9191–9193.

[18] Tang A W, Teng F, Gao Y H, et al. White light emission from organic-inorganic hererostructure devices by using CdSe quantum dots as emitting layer. J. Lumin., 2007, 122: 649–651.

[19] Kobayashi S, Tani Y, Kawazoe H. Quantum dot activated all-inorganic electroluminescent device fabricated using solution-synthesized CdSe/ZnS nanocrystals. Japanese Journal of Applied Physics Part 2-Letters & Express Letters, 2007, 46(36-40): L966–L969.