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. 2019 May 11;10(5):318.
doi: 10.3390/mi10050318.

Silicon Quantum Dot Light Emitting Diode at 620 Nm

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Free PMC article

Silicon Quantum Dot Light Emitting Diode at 620 Nm

Hiroyuki Yamada et al. Micromachines (Basel). .
Free PMC article

Abstract

Here we report a quantum dot light emitting diode (QLED), in which a layer of colloidal silicon quantum dots (SiQDs) works as the optically active component, exhibiting a strong electroluminescence (EL) spectrum peaking at 620 nm. We could not see any fluctuation of the EL spectral peak, even in air, when the operation voltage varied in the range from 4 to 5 V because of the possible advantage of the inverted device structure. The pale-orange EL spectrum was as narrow as 95 nm. Interestingly, the EL spectrum was narrower than the corresponding photoluminescence (PL) spectrum. The EL emission was strong enough to be seen by the naked eye. The currently obtained brightness (∼4200 cd/m2), the 0.033% external quantum efficiency (EQE), and a turn-on voltage as low as 2.8 V show a sufficiently high performance when compared to other orange-light-emitting Si-QLEDs in the literature. We also observed a parasitic emission from the neighboring compositional layer (i.e., the zinc oxide layer), and its intensity increased with the driving voltage of the device.

Keywords: light emitting diode; quantum dot; silicon nanocrystals.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Photoluminescence (PL) and plots of F[R] vs. wavelength for the powder form of the decane-terminated silicon quantum dot (SiQD-De) specimen. F[R] of the powder form is the Kubelka−Munk function, with F[R] = (1 − R)2/2R.
Figure 2
Figure 2
Schematic representation and flat energy band diagram of the pale-orange-light-emitting silicon quantum dot light emitting diode (Si-QLED) with an inverted device structure.
Figure 3
Figure 3
(a) Device I−V characteristics (black line) and photodiode I−V characteristics (red line), (b) luminance−current density characteristics, and (c) a typical electroluminescence (EL) spectrum at the operation voltage of 5 V (PL spectrum of the corresponding SiQD-De dispersed in chloroform). A photograph demonstrates a representative pale-orange-light-emitting quantum dot light emitting diode (QLED).
Figure 4
Figure 4
EL spectra at three different bias voltages.
Figure 5
Figure 5
External quantum efficiency (EQE) versus device current density.

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