High-Performance White Light-Emitting Diodes over 150 lm/W Using Near-Unity-Emitting Quantum Dots in a Liquid Matrix

Abstract

In the next decade, we will witness the replacement of a majority of conventional light sources with light-emitting diodes (LEDs). Efficient LEDs other than phosphors can enhance their functionality and meet different lighting needs. Quantum dots (QDs) have high potential for future LED technology due to their sensitive band-gap tuning via the quantum confinement effect and compositional control, high photoluminescence quantum yield (PLQY), and mass-production capacity. Herein, we demonstrate white LEDs using QDs that reach over 150 lumens per electrical Watt. For that we synthesized green- and red-emitting ZnCdSe/ZnSe core/shell QDs by low-temperature nucleation, high-temperature shell formation, and postsynthetic trap-state removal. Their cadmium concentration is lower than 100 ppm, satisfying the current EU RoHS regulations, and their PLQY reaches a high level of 94%. The PLQY of QDs is maintained within the device on blue LED via liquid injection, and their integration at optimized optical densities leads to 129.6 and 170.4 lm/W for red-green-blue (RGB)- and green-blue (GB)-based white LEDs, respectively. Our simulations further showed that an efficiency level of over 230 lm/W is achievable using ultraefficient blue LED pumps. The simple fabrication and high performance of white LEDs using QD liquids show high promise for next-generation lighting devices.

Indium arsenide quantum dots: an alternative to lead-based infrared emitting nanomaterials

“…Electroluminescence (EL) has been one of the prime applications of colloidal QDs. While QD LEDs emitting in the visible spectral region are well-established, 2,164,[191][192][193] NIR QD LED are still not fully developed. InAs QDs represent one of the most appealing QDs for the fabrication of NIR LEDs, since they are fully RoHS-complaint and capable of fully covering the NIR spectrum.…”

Quantum Dot to Nanorod Transition for Efficient White-Light-Emitting Diodes with Suppressed Absorption Losses

“…Second, the device architecture may retain the optical features of the nanomaterials such as emission bandwidth and quantum efficiency without any shift and efficiency loss caused by the host-material effect. Thus, the liquid-state devices can achieve high efficiencies that are comparable with or even above the solid-state devices using nanocrystals . Third, the host material does not require any curing process with heat or light, which may photobleach the fluorophores.…”

“…For the green spectral range, we synthesized ZnCdSe/ZnSe core/shell QDs with the PLQY of 90% in the solution state based on our recently published study. 40 Although CdSe/CdS QDs show near-unity photoluminescence due to the effective passivation and small lattice mismatch between CdSe and CdS (3.9%), 41,42 their photoluminescence tunability is limited to the red spectral region due to its quasi-type II band alignment. Alternatively, we selected ternary ZnCdSe QDs that allow for precisely tuning the photoluminescence spectrum in the green spectral range by adjusting the Cd:Zn molar ratios.…”

“…Thus, the liquid-state devices can achieve high efficiencies that are comparable with or even above the solid-state devices using nanocrystals. 40 Third, the host material does not require any curing process with heat or light, which may photobleach the fluorophores. Due to these advantageous properties, we chose to work with liquid-state devices.…”

“…The ZnSe shelling procedure to achieve ZnCdSe/ZnSe QDs was performed based on the method of the recent study in our group. 40 A syringe pump was used to inject the Se-SUS precursor (0.6 mmol) into the reaction flask, which contains ZnCdSe core QDs, at a rate of 12 mL•h −1 while the reaction flask was heated to 310 °C. The procedure for shell formation was finished by maintaining the temperature at 310 °C for 30 min after the injection was finished.…”