Abstract
Graphene quantum dots (GQDs) with an average diameter of 3.5 nm were prepared via pulsed laser ablation. The synthesized GQDs can improve the optical and electrical properties of InGaN/InAlGaN UV light emitting diodes (LEDs) remarkably. An enhancement of electroluminescence and a decrease of series resistance of LEDs were observed after incorporation of GQDs on the LED surface. As the GQD concentration is increased, the emitted light (series resistance) in the LED increases (decreases) accordingly. The light output power achieved a maximum increase as high as 71% after introducing GQDs with the concentration of 0.9 mg/ml. The improved performance of LEDs after the introduction of GQDs is explained by the photon recycling through the light extraction from the waveguide mode and the carrier transfer from GQDs to the active layer.
Highlights
Phosphors in white light emitting diodes (WLEDs). The former has been implemented by mixing of methylene blue functionalized Graphene quantum dots (GQDs) (MB-GQDs) and poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), which leads to a decrease of the turn-on voltage by 33% compared to the OLED with pure MEH-PPV15
We study the influence of the LED performance in InGaN/InAlGaN UV LEDs after introduction of GQDs
The GQDs shows relatively strong absorption in the UV region, which is advantageous for the photon recycling effect in the InGaN/InAlGaN UV LEDs
Summary
Phosphors in white light emitting diodes (WLEDs). The former has been implemented by mixing of methylene blue functionalized GQDs (MB-GQDs) and poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), which leads to a decrease of the turn-on voltage by 33% compared to the OLED with pure MEH-PPV15. Photon recycling effect is usually unapparent in the quantum-well (QW) based LEDs because of low optical absorption in the thin QW layer[18]. This effect could be enhanced through an interaction between a high-absorption material and an evanescent field from optical cavity modes. GQDs provide high optical absorption in the UV region and they can be a candidate for improving the photon recycling in UV GaN-based devices. The improvement of electrical and optical properties in the GQD-LED composite is explained by photon recycling from the waveguide modes
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