J. Semicond. > 2018, Volume 39 > Issue 6 > 061008, doi: 10.1088/1674-4926/39/6/061008
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SPECIAL ISSUE ON Si-BASED MATERIALS AND DEVICES

Light-emitting diodes based on colloidal silicon quantum dots

Shuangyi Zhao, Xiangkai Liu, Xiaodong Pi and Deren Yang

+ Author Affiliations

 Corresponding author: Xiaodong Pi, Email: xdpi@zju.edu.cn

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Abstract: Colloidal silicon quantum dots (Si QDs) hold great promise for the development of printed Si electronics. Given their novel electronic and optical properties, colloidal Si QDs have been intensively investigated for optoelectronic applications. Among all kinds of optoelectronic devices based on colloidal Si QDs, QD light-emitting diodes (LEDs) play an important role. It is encouraging that the performance of LEDs based on colloidal Si QDs has been significantly increasing in the past decade. In this review, we discuss the effects of the QD size, QD surface and device structure on the performance of colloidal Si-QD LEDs. The outlook on the further optimization of the device performance is presented at the end.

Key words: quantum dots, optoelectronic devices, light-emitting diode



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Fig. 1.  (Color online) Schematic of the typical process of hydrosilylation for Si QDs.

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Fig. 2.  (Color online) Gas-phase hydrosilylation of Si QDs using styrene and acetylene.

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Fig. 3.  (Color online) (a) Dependence of the PL energy (bandgap) on the size of dodecene-hydrosilylated Si QDs. (b) PL QY of a series of dodecene-hydrosilylated Si QDs with different sizes. (c) Dependence of the PL lifetime on the bandgap for dodecene-hydrosilylated Si QDs.

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Fig. 4.  (Color online) Photograph of 3–4 nm Si QDs functionalized with various surface groups dispersed in toluene under UV illumination. From left to right: blue, dodecylamine; blue-green, acetal; green, diphenylamine; yellow, TOPO; orange, dodecyl (air); red, dodecyl (inert).

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Fig. 5.  (Color online) (a) Scheme of the PL from Si QDs with nitrogen-containing ligands at the surface. (b) Scheme of the PL from conventional Si quantum dots.

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Fig. 6.  (Color online) (a) Schematic of the Si QDs hydrosilylation with 1-octene and allylbenzene. (b) The PL decay curves of octyl-Si QDs and PhPr-Si QDs. (c) Optical power density (P) versus voltage (V) for an octyl-Si QD LED and a PhPr-Si QD LED. (d) EQE versus voltage (V) for an octyl-Si QD LED and a PhPr-Si QD LED.

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Fig. 7.  (Color online) Size-separated Si QDs and their corresponding PL spectra. (a) Si QDs dispersed in toluene showing intense luminescence from the deep red to the yellow spectral region. (b) PL spectra of the three samples used for Si-QD LEDs fabrication. Excitation: (a) 365 nm LED and (b) 355 nm Nd:YAG laser. (c) High-resolution cross-section TEM image of a real device (scale bar: 50 nm).

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Fig. 8.  (Color online) (a) External quantum efficiency (EQE) of devices containing different-sized Si QDs as emitters. (b) EL intensity of size-separated and non-size-separated Si QDs over time at constant current of 1.6 mA/cm2.

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Fig. 9.  (a) Current–voltage characteristics for hybrid Si-QD LEDs having emissive layers spun-cast from solutions with varying Si QDs concentration. (b) EL spectra for the devices (a) at an applied current density of 10 mA/cm2. The arrow denotes the direction of increasing Si-QD concentration. (c) EQE for a hybrid Si-QD LEDs with an emissive layer spun-cast from a Si-QD solution with the concentration of 20 mg/mL.

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Fig. 10.  Luminance and current density versus voltage plots of devices with PVK and PEDOT:PSS as HTL, respectively. The insets were the proposed energy level diagrams of the devices at zero field.

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Fig. 11.  Impact of the electron-transporting materials. (a) Proposed energy level diagram under zero applied bias for devices containing Si QDs with a diameter of 5 nm, and an ETL consisting of either Alq3, TCTA, or CBP. (b) EQE versus current density for devices containing either Alq3 (solid line), TCTA (broken line), or CBP (dotted line). (c) Current density voltage and optical power density voltage characteristics for the devices in (b).

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Fig. 12.  (Color online) (a) Schematic of the structure of a Si-QD LED. (b) Work function of ITO (WA) modified by HAT-CN/MoO3 with varying film thickness.

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Fig. 13.  (Color online) EQE versus current density characteristics for Si-QD LEDs without and with (a) HAT-CN and (b) MoO3 interlayers.

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Fig. 14.  (Color online) Stability data for Si-QD LEDs without any interlayer, with ~5 nm thick HAT-CN, and with ~3 nm thick MoO3 at the operating voltage of 8 V.

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Fig. 15.  (Color online) (a) Schematic of the structure of an all-inorganic Si-QD LED. (b) Flat-band energy-level diagram. (c) Power density versus voltage for all-inorganic Si-QD LEDs without and with Al2O3. (d) EQE versus current density for all inorganic Si-QD LEDs without and with Al2O3.

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Fig. 16.  (Color online) (a) PL spectra and (b) PL decay curves of Si QDs on NiO and Al2O3/NiO. The thickness of Al2O3 changed from 1.6 to 9.0 nm.

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Fig. 17.  (Color online) (a) Current density and power density versus voltage for flexible Si-QD LEDs without and with 5.7 nm thick Al2O3. (b) EQE versus current density for flexible Si-QD LEDs without and with 5.7 nm thick Al2O3. (c) Operation lifetime and (d) storage lifetime for Si-QD LEDs with 5.7 nm Al2O3. The driving voltage was 8 V.

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Fig. 18.  (Color online) (a) A schematic structure diagram for the modified Si-QD LEDs with the structure of glass/ITO/PEI/ZnO NPs/SiQDs/TAPC/MoO3/Al. (b) The UPS spectra of pristine ITO and PEI modified ITO.

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Fig. 19.  (Color online) (a) External quantum efficiency versus current density, (b) optical power density versus voltage characteristics for the modified Si QD-LEDs (red circles) and the reference Si QD-LEDs (blue rectangles).

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    Received: 07 November 2017 Revised: 25 December 2017 Online: Accepted Manuscript: 15 March 2018Published: 01 June 2018

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      Article Navigation >  Journal of Semiconductors  > 2018  >  39(6): 061008
      Shuangyi Zhao, Xiangkai Liu, Xiaodong Pi, Deren Yang. Light-emitting diodes based on colloidal silicon quantum dots[J]. Journal of Semiconductors, 2018, 39(6): 061008. doi: 10.1088/1674-4926/39/6/061008 S Y Zhao, X K Liu, X D Pi, D R Yang. Light-emitting diodes based on colloidal silicon quantum dots[J]. J. Semicond., 2018, 39(6): 061008. doi: 10.1088/1674-4926/39/6/061008.Export: BibTex EndNote
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      Shuangyi Zhao, Xiangkai Liu, Xiaodong Pi, Deren Yang. Light-emitting diodes based on colloidal silicon quantum dots[J]. Journal of Semiconductors, 2018, 39(6): 061008. doi: 10.1088/1674-4926/39/6/061008

      S Y Zhao, X K Liu, X D Pi, D R Yang. Light-emitting diodes based on colloidal silicon quantum dots[J]. J. Semicond., 2018, 39(6): 061008. doi: 10.1088/1674-4926/39/6/061008.
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      Light-emitting diodes based on colloidal silicon quantum dots

      doi: 10.1088/1674-4926/39/6/061008

      • State Key Laboratory of Silicon Materials and School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China

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      • Corresponding author: Email: xdpi@zju.edu.cn
      • Received Date: 2017-11-07
      • Revised Date: 2017-12-25
      • Published Date: 2018-06-01

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