Highly Efficient Cadmium-Free Quantum Dot Light-Emitting Diodes Enabled by the Direct Formation of Excitons within InP@ZnSeS Quantum Dots

Abstract

We demonstrate bright, efficient, and environmentally benign InP quantum dot (QD)-based light-emitting diodes (QLEDs) through the direct charge carrier injection into QDs and the efficient radiative exciton recombination within QDs. The direct exciton formation within QDs is facilitated by an adoption of a solution-processed, thin conjugated polyelectrolyte layer, which reduces the electron injection barrier between cathode and QDs via vacuum level shift and promotes the charge carrier balance within QDs. The efficient radiative recombination of these excitons is enabled in structurally engineered InP@ZnSeS heterostructured QDs, in which excitons in the InP domain are effectively passivated by thick ZnSeS composition-gradient shells. The resulting QLEDs record 3.46% of external quantum efficiency and 3900 cd m(-2) of maximum brightness, which represent 10-fold increase in device efficiency and 5-fold increase in brightness compared with previous reports. We believe that such a comprehensive scheme in designing device architecture and the structural formulation of QDs provides a reasonable guideline for practical realization of environmentally benign, high-performance QLEDs in the future.

Origin of Work Function Modification by Ionic and Amine‐Based Interface Layers

“…[13][14][15][16][17]28 ] Increasing, [ 15 ] constant, [ 13,16 ] and decreasing [ 17 ] work function shifts have all been reported. Part of these works comprises the characterization of complete devices, which complicates the interpretation as charge transport is involved as well.…”

“…Characterization of the open-circuit voltage circumvents this issue, although also the open-circuit voltage depends on many factors. Characterization of WMLs by inherently current-less techniques like SKPM [ 13,15,28 ] excludes these problems, but still one must ensure that the substrate is completely covered. Incomplete coverage will result in intermediate results.…”

Tuning the Lattice Parameter of InxZnyP for Highly Luminescent Lattice-Matched Core/Shell Quantum Dots

“…InP-based QDs are among the most investigated nontoxic Cd-free systems, owing to their comparable emission range. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] However, in terms of PL QY and PL stability they cannot yet compete with Cd-based QDs.…”

“…Although the addition of Zn to the synthesis of InP nanocrystals has become common practice in the last years, [11][12][13][14][15][16][17][21][22][23][24][25] very little has been reported on the actual role of the Zn. The few reports on this topic have focused on the effect on the optical properties, but structural aspects were not investigated.…”

Interfacial engineering of core/shell heterostructured nanocrystal quantum dots for light-emitting applications

“…In the last two decades, the structures of NQDs evolved into sophisticated heterostructures, boosting their optical performances and photophysical stabilities [19][20][21][22][23][24][25][26][27]. As a result of the multilateral efforts, core/shell heterostructured NQDs displaying almost 100% efficiency upon the excitation of both optical [24] or electrical pumping have been successfully realized.…”