Synthesis of Alloyed ZnSeTe Quantum Dots as Bright, Color-Pure Blue Emitters

Abstract

Considering a strict global environmental regulation, fluorescent quantum dots (QDs) as key visible emitters in the next-generation display field should be compositionally non-Cd. When compared to green and red emitters obtainable from size-controlled InP QDs, development of non-Cd blue QDs remains stagnant. Herein, we explore the synthesis of non-Cd, ZnSe-based QDs with binary and ternary compositions toward blue photoluminescence (PL). First, the size increment of binary ZnSe QDs is attempted by a multiply repeated growth until blue PL is attained. Although this approach offers a relevant blue color, excessively large-sized ZnSe QDs inevitably entail a low PL quantum yield. As an alternative strategy to the above size enlargement, the alloying of high-band gap ZnSe with lower-band gap ZnTe in QD synthesis is carried out. These alloyed ternary ZnSeTe QDs after ZnS shelling exhibit a systematically tunable PL of 422–500 nm as a function of Te/Se ratio. Analogous to the state-of-the-art heterostructure of InP QDs with a double-shelling scheme, an inner shell of ZnSe is newly inserted with different thicknesses prior to an outer shell of ZnS, where the effects of the thickness of ZnSe inner shell on PL properties are examined. Double-shelled ZnSeTe/ZnSe/ZnS QDs with an optimal thickness of the ZnSe inner shell are then employed for all-solution-processed fabrication of a blue QD light-emitting diode (QLED). The present blue QLED as the first ZnSeTe QD-based device yields a peak luminance of 1195 cd/m2, a current efficiency of 2.4 cd/A, and an external quantum efficiency of 4.2%, corresponding to the record values reported from non-Cd blue devices.

Blue quantum dot-based electroluminescent light-emitting diodes

“…This work will pave the way for the realization of next-generation non-Cd QD-LED displays in the future. 102…”

“…(c) Spectral comparison of the PL of a dilute ZnSeTe/ZnSe/ZnS QD dispersion with the EL collected at 7 V. (d) Current efficiency and Z EQE as a function of current density for QD-LEDs with an ITO/PEDOT:PSS/PVK/ZnSeTe/ZnSe/ZnS QDs/ ZnMgO/Al structure. Reproduced with permission 102. Copyright 2019, American Chemical Society.…”

How Will Quantum Dots Enable Next‐Gen Display Technologies?

“…Other approaches have been proposed, such as a partial chemical substitution of selenium by tellurium to produce an alloy ZnSe(Te) 12 . However, this also creates difficulty in controlling the precise alloy composition and would result in a wider‐light emission spectrum that would reduce the display's available color gamut.…”

58‐3: Distinguished Paper: High‐Efficient Quantum‐Dot Light‐Emitting Diodes with Blue Cadmium‐free Quantum Dots

“…However this also comes with degradation of the crystal quality and generation of non-radiative defects. One solution proposed is to add Tellurium (Te) to ZnSe QDs as reported in [11]. This creates difficulty in controlling a precise alloy composition resulting in wider emission linewidth.…”

“…the light emission properties of the most efficient blue emitting QD-LEDs reported to date[9,10,11]. Blue QD-LEDs reported in the literature…”