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.
Highlights
Solid-state lighting in the form of light emitting diodes (LEDs) is expected to reduce global energy consumption in the lighting industry [1,2]
Due to the complete ban of these elements in the future, recent efforts have shifted toward fabricating heavy-metal-free quantum dot light emitting diode (QLED)
Xu and co-workers reported a pale-orange-emitting QLED in which colloidal quantum dots (QDs) consisting of CuInS2-ZnS-alloyed (ZCIS) cores and ZnSe/ZnS double shells work as an active layer [12]
Summary
Solid-state lighting in the form of light emitting diodes (LEDs) is expected to reduce global energy consumption in the lighting industry [1,2]. The best values of external quantum efficiencies (EQEs) of red-emitting quantum dot light emitting diodes (QLEDs) with conventional and inverted structures are currently 20.5% and 18.0%, respectively [9,10] These magnitudes are close to an energy conversion efficiency of a mercury lamp which works as a benchmark for the industry. The enhancement is postulated to arise from an increase in the radiative recombination rate [19], a dramatic reduction of the nonradiative channels [20,23], or a bandgap modulation from indirect to direct transitions [24] Such high values of the PLQY are suitable as active layers for the QLED. The Si-QLED exhibits the EL spectrum peaking at 620 nm, which is included in the pale-orange emission wavelength range
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