journal article·2020-12Open access

Optimization of the electron transport layer in quantum dot light-emitting devices

Gary Zaiats, Shingo Ikeda, Prashant V. Kamat

NPG Asia Materials· Volume 12· Issue 1

Abstract

Abstract Quantum dot light-emitting devices have emerged as an important technology for display applications. Their emission is a result of recombination between positive and negative charge carriers that are transported through the hole and electron conductive layers, respectively. The selection of electron or hole transport materials in these devices not only demands the alignment of energy levels between the layers but also balances the flow of electrons and holes toward the recombination sites. In this work, we examine a method for device optimization through control of the charge carrier kinetics. We employ impedance spectroscopy to examine the mobility of charge carriers through each of the layers. The derived mobility values provide a path to estimate the transition time of each charge carrier toward the emitting layer. We suggest that an optimal device structure can be obtained when the transition times of both charge carriers toward the active layer are similar. Finally, we examine our hypothesis by focusing on thickness optimization of the electron transport layer.
Source: crossref · Quality: baseline

Research context

OpenAlex topics: Quantum Dots Synthesis And Properties · Chalcogenide Semiconductor Thin Films · Molecular Junctions and Nanostructures

SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.

References (52)

Show source-provided references
1. Zaiats, G., Ikeda, S., Kinge, S. & Kamat, P. V. Quantum dot light-emitting devices: beyond alignment of energy levels. ACS Appl. Mater. Interfaces 9, 30741–30745 (2017).10.1021/acsami.7b07893 ↗
2. Kim, H. et al. Characteristics of CuInS2/ZnS quantum dots and its application on LED. J. Cryst. Growth 326, 90–93 (2011).10.1016/j.jcrysgro.2011.01.059 ↗
3. Kim, J.-H. & Yang, H. All-solution-processed, multilayered CuInS2/ZnS colloidal quantum-dot-based electroluminescent device. Opt. Lett. 39, 5002–5005 (2014).10.1364/OL.39.005002 ↗
4. Qian, L., Zheng, Y., Xue, J. & Holloway, P. H. Stable and efficient quantum-dot light-emitting diodes based on solution-processed multilayer structures. Nat. Photonics 5, 543–548 (2011).10.1038/nphoton.2011.171 ↗
5. Coe, S., Woo, W. K., Bawendi, M. & Bulovic, V. Electroluminescence from single monolayers of nanocrystals in molecular organic devices. Nature 420, 800–803 (2002).10.1038/nature01217 ↗
6. Chuang, C.-H. M., Brown, P. R., Bulović, V. & Bawendi, M. G. Improved performance and stability in quantum dot solar cells through band alignment engineering. Nat. Mater. 13, 796–801 (2014).10.1038/nmat3984 ↗
7. Mashford, B. S. et al. High-efficiency quantum-dot light-emitting devices with enhanced charge injection. Nat. Photonics 7, 407–412 (2013).10.1038/nphoton.2013.70 ↗
8. Chen, H. et al. All-solution-processed quantum dot light emitting diodes based on double hole transport layers by hot spin-coating with highly efficient and low turn-on voltage. ACS Appl. Mater. Interfaces 10, 29076–29082 (2018).10.1021/acsami.8b06917 ↗
9. Shirasaki, Y., Supran, G. J., Bawendi, M. G., Bulovic, V. & Bulović, V. Emergence of colloidal quantum-dot light-emitting technologies. Nat. Photonics 7, 13–23 (2013).10.1038/nphoton.2012.328 ↗
10. Zhang, Y. et al. Employing heavy metal-free colloidal quantum dots in solution-processed white light-emitting diodes. Nano Lett. 11, 329–332 (2011).10.1021/nl1021442 ↗
11. Marin, R. et al. Mercaptosilane-passivated CuInS2 quantum dots for luminescence thermometry and luminescent labels. ACS Appl. Nano Mater. 2, 2426–2436 (2019).10.1021/acsanm.9b00317 ↗
12. Li, L. et al. Highly luminescent CuInS2/ZnS core/shell nanocrystals: cadmium-free quantum dots for in vivo imaging. Chem. Mater. 21, 2422–2429 (2009).10.1021/cm900103b ↗
13. Yoon, S.-Y. et al. Systematic and extensive emission tuning of highly efficient Cu–In–S-based quantum dots from visible to near infrared. Chem. Mater. 31, 2627–2634 (2019).10.1021/acs.chemmater.9b00550 ↗
14. Steckel, J. S. et al. Color-saturated green-emitting QD-LEDs. Angew. Chem. Int. Ed. Engl. 45, 5796–5799 (2006).10.1002/anie.200600317 ↗
15. Anikeeva, P. O., Halpert, J. E., Bawendi, M. G. & Bulović, V. Quantum dot light-emitting devices with electroluminescence tunable over the entire visible spectrum. Nano Lett. 9, 2532–2536 (2009).10.1021/nl9002969 ↗
16. Lee, K.-H. et al. Highly efficient, color-pure, color-stable blue quantum dot light-emitting devices. ACS Nano 7, 7295–7302 (2013).10.1021/nn402870e ↗
17. Park, J.-S. et al. Alternative patterning process for realization of large-area, full-color, active quantum dot display. Nano Lett. 16, 6946–6953 (2016).10.1021/acs.nanolett.6b03007 ↗
18. Dai, X. et al. Solution-processed, high-performance light-emitting diodes based on quantum dots. Nature 515, 96–99 (2014).10.1038/nature13829 ↗
19. Zaiats, G., Kinge, S., Kamat, P. V. Origin of dual photoluminescence states in ZnS-CuInS2 alloy nanostructures. J. Phys. Chem. 120 19461–19469 (2016).10.1021/acs.jpcc.6b01905 ↗
20. Jara, D. H., Yoon, S. J., Stamplecoskie, K. G. & Kamat, P. V. Size-dependent photovoltaic performance of CuInS2 quantum dot-sensitized solar cells. Chem. Mater. 26, 7221–7228 (2014).10.1021/cm5040886 ↗
21. Aldakov, D., Lefrancois, A. & Reiss, P. Ternary and quaternary metal chalcogenide nanocrystals: synthesis, properties and applications. J. Mater. Chem. C. 1, 3756–3776 (2013).10.1039/c3tc30273c ↗
22. Li, J. et al. Alloyed CuInS2 –ZnS nanorods: synthesis, structure and optical properties. CrystEngComm 17, 5634–5643 (2015).10.1039/C5CE00380F ↗
23. Zaiats, G., Kinge, S. & Kamat, P. V. Origin of dual photoluminescence states in ZnS-CuInS2 alloy nanostructures. J. Phys. Chem. C. 120, 10641–10646 (2016).10.1021/acs.jpcc.6b01905 ↗
24. Torimoto, T. et al. Facile synthesis of ZnS−AgInS2 solid solution nanoparticles for a color-adjustable luminophore. J. Am. Chem. Soc. 129, 12388–12389 (2007).10.1021/ja0750470 ↗
25. Dai, M. et al. Tunable photoluminescence from the visible to near-infrared wavelength region of non-stoichiometric AgInS2 nanoparticles. J. Mater. Chem. 22, 12851 (2012).10.1039/c2jm31463k ↗
26. Stroyuk, O. et al., A. Origin and dynamics of highly efficient broadband photoluminescence of aqueous glutathione-capped size-selected Ag–In–S quantum dots. J. Phys. Chem. C 25, 13648–13658 (2018).10.1021/acs.jpcc.8b00106 ↗
27. Hoffman, J. B., Choi, H. & Kamat, P. V. Size-dependent energy transfer pathways in cdse quantum dot–squaraine light-harvesting assemblies: förster versus dexter. J. Phys. Chem. C. 118, 18453–18461 (2014).10.1021/jp506757a ↗
28. Luther, J. M. et al. Structural, optical, and electrical properties of self-assembled films of pbse nanocrystals treated with 1,2-ethanedithiol. ACS Nano 2, 271–280 (2008).10.1021/nn7003348 ↗
29. Hughes, B. K. et al. Control of PbSe quantum dot surface chemistry and photophysics using an alkylselenide ligand. ACS Nano 6, 5498–5506 (2012).10.1021/nn301405j ↗
30. Bai, Z. et al. Hydroxyl-terminated CuInS2-based quantum dots: toward efficient and bright light emitting diodes. Chem. Mater. 28, 1085–1091 (2016).10.1021/acs.chemmater.5b04480 ↗
31. Lee, K. H. et al. Highly efficient, color-reproducible full-color electroluminescent devices based on red/green/blue quantum dot-mixed multilayer. ACS Nano 9, 10941–10949 (2015).10.1021/acsnano.5b05513 ↗
32. Trizio, L. D. E. et al. Strongly fluorescent quaternary Cu–In–Zn–S nanocrystals prepared from Cu1-x InS2 nanocrystals by partial cation exchange. Chem. Mater. 24, 2400–2406 (2012).10.1021/cm301211e ↗
33. Akkerman, Q. A. et al. From binary Cu2S to ternary Cu–In–S and quaternary Cu–In–Zn–S nanocrystals with tunable composition via partial cation exchange. ACS Nano 9, 521–531 (2015).10.1021/nn505786d ↗
34. Nelson, H. D. & Gamelin, D. R. Valence-band electronic structures of Cu + -doped ZnS, alloyed Cu–In–Zn–S, and ternary CuInS2 nanocrystals: a unified description of photoluminescence across compositions. J. Phys. Chem. C. 122, 18124–18133 (2018).10.1021/acs.jpcc.8b05286 ↗
35. Pan, J. et al. Size tunable ZnO nanoparticles to enhance electron injection in solution processed QLEDs. ACS Photonics 3, 215–222 (2016).10.1021/acsphotonics.5b00267 ↗
36. Fong, H. H., Lun, K. C. & So, S. K. Hole transports in molecularly doped triphenylamine derivative. Chem. Phys. Lett. 353, 407–413 (2002).10.1016/S0009-2614(02)00053-2 ↗
37. Chen, B. et al. Template synthesis of CuInS2 nanocrystals from In2S3 nanoplates and their application as counter electrodes in dye-sensitized solar cells. Chem. Mater. 27, 5949–5956 (2015).10.1021/acs.chemmater.5b01971 ↗
38. Coe-Sullivan, S., Woo, W.-K., Steckel, J. S., Bawendi, M. & Bulović, V. Tuning the performance of hybrid organic/inorganic quantum dot light-emitting devices. Org. Electron. 4, 123–130 (2003).10.1016/j.orgel.2003.08.016 ↗
39. Kern, R., Sastrawan, R., Ferber, J., Stangl, R. & Luther, J. Modeling and interpretation of electrical impedance spectra of dye solar cells operated under open-circuit conditions. Electrochim. Acta 47, 4213–4225 (2002).10.1016/S0013-4686(02)00444-9 ↗
40. Mora-Seró, I. et al. Recombination rates in heterojunction silicon solar cells analyzed by impedance spectroscopy at forward bias and under illumination. Sol. Energy Mater. Sol. Cells 92, 505–509 (2008).10.1016/j.solmat.2007.11.005 ↗
41. Mora-Seró, I. et al. Implications of the negative capacitance observed at forward bias in nanocomposite and polycrystalline solar cells. Nano Lett. 6, 640–650 (2006).10.1021/nl052295q ↗
42. Rath, A. K., Lasanta, T., Bernechea, M., Diedenhofen, S. L. & Konstantatos, G. Determination of carrier lifetime and mobility in colloidal quantum dot films via impedance spectroscopy. Appl. Phys. Lett. 104, 63504 (2014).10.1063/1.4865089 ↗
43. Das, M. et al. Equivalent circuit analysis of Al/rGO-TiO2 metal-semiconductor interface via impedance spectroscopy: graphene induced improvement in carrier mobility and lifetime. Mater. Sci. Semicond. Process. 82, 104–111 (2018).10.1016/j.mssp.2018.03.039 ↗
44. Scher, H. Time scale invariance in transport and relaxation. AIP Conf. Proc. 256, 485–494 (1992).10.1063/1.42416 ↗
45. Long, Q., Dinca, S. A., Schiff, E. A., Yu, M. & Theil, J. Electron and hole drift mobility measurements on thin film CdTe solar cells. Appl. Phys. Lett. 105, 42106 (2014).10.1063/1.4891846 ↗
46. Maynard, B. et al. Electron and hole drift mobility measurements on methylammonium lead iodide perovskite solar cells. Appl. Phys. Lett. 108, 173505 (2016).10.1063/1.4948344 ↗
47. Yun, H. J. et al. Charge-transport mechanisms in CuInSexS2–x quantum-dot films. ACS Nano 12, 12587–12596 (2018).10.1021/acsnano.8b07179 ↗
48. Draguta, S., McDaniel, H. & Klimov, V. I. Tuning carrier mobilities and polarity of charge transport in films of CuInSexS2-x quantum dots. Adv. Mater. 27, 1701–1705 (2015).10.1002/adma.201404878 ↗
49. Gong, X. et al. Highly efficient quantum dot near-infrared light-emitting diodes. Nat. Photonics 10, 253 (2016).10.1038/nphoton.2016.11 ↗
50. Kim, J.-H. et al. White electroluminescent lighting device based on a single quantum dot emitter. Adv. Mater. 28, 5093–5098 (2016).10.1002/adma.201600815 ↗
51. Heun, S. & Borsenberger, P. M. A comparative study of hole transport in vapor-deposited molecular glasses of N,N′,N″,N‴-tetrakis(4-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine. Chem. Phys. 200, 245–255 (1995).10.1016/0301-0104(95)00192-Q ↗
52. Rutledge, S. A. & Helmy, A. S. Carrier mobility enhancement in poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) having undergone rapid thermal annealing. J. Appl. Phys. 114, 133708 (2013).10.1063/1.4824104 ↗