Liquid QDs for high efficiency LEDs
Their approach described in the paper “Quantum dot white LEDs with high luminous efficiency” published in the Optica journal consists in capping a blue LED with a transparent PDMS polymeric lens which they then injected with a liquid mix of colloidal quantum dots for colour conversion, yielding a white light.
green spheres represent red- and green-emitting
QDs in a liquid, respectively. The combination of
red and green emission by QDs and blue emission
by a blue LED die generates white light.
The polymer lens was mechanically stable and conformable enough to recover its surface against the needle holes after the injection, preventing any leaks.
By using high quantum yield (QY) and tuneable QDs directly from the synthesis batch in their liquid state, the researchers were able to suppress the host material effect and reabsorption attributed to conventional QD host matrices when the devices are realized in the solid state.
The integration of as-synthesized liquid QDs without any chemical or interfacial modification enables to preserve their high quantum yield, leading to the most efficient QD-based white LED reported to date, explain the authors.
The paper reports an RGB white LED with a luminous efficiency of 64 lm/W and 105 lm/W for a green-blue (GB)-based white light generation, identifying the liquid-state integration as reason behind a two-fold and six-fold enhancement of efficiency compared to the incorporation of QDs in polydimethylsiloxane film and close-packed formation, respectively.
The researchers also predicted theoretically that the luminous efficiency of liquid QD-LEDs could reach over 200 lm/W when combining state-of-the-art blue LED die with an EQE of 85% and red- and green-emitting QDs with a QY of unity.
Koç University – www.ku.edu.tr/en
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