Abstract
Colloidal semiconductor nanocrystals (NCs) attract significant interest in recent years due to their narrow and tunable emission wavelength in the visible range, as well as high photoluminescence quantum yield (PLQY), which are highly desired in display technologies. The high-quality NCs have been recognized as vital luminescent materials in realizing next-generation display devices. With further development, NCs with near-unity PLQY have been successfully synthesized through engineering of the core/shell heterostructure. However, as the external quantum efficiency (EQE) of the nanocrystal light-emitting diodes (LEDs) approaches the theoretical limit of about 20%, the low out-coupling factor proposes a challenge of enhancing the performance of a device when using the spherical QDs. Hence, the anisotropic NCs like nanoplatelets (NPLs) are proposed as promising solutions to improve the performance of nanocrystal LEDs. In this review, we will summarize the synthetic strategies of two-dimensional (2D) NPLs at first. Then, we will introduce fundamental concepts of LEDs, the main approaches to realize LEDs based on nanoplatelets, and the recent progress. Finally, the challenges and opportunities of LEDs based on anisotropic NCs are also presented.
Highlights
In the past few decades, colloidal nanocrystals (NCs) have drawn considerable attention due to their solution-processable and low-cost synthesis, high photoluminescence quantum yield (PLQY), and high color purity, as well as tunable emission wavelengths [1,2,3,4]
To improve the charge injection and transport, the long ligands of the as-synthesized NPLs were exchanged to shorter ones (i.e., 3-mercaptopropionic acid), leading to about 2-fold increase in external quantum efficiency (EQE) of 0.63% and a maximum luminance of 4499 cd m−2, the PLQY decreased by 40% after the ligand exchange (Figure 5(d))
The exciton quenching at the interface of charge transport layer/NPLs has been greatly suppressed, and the potential energy barrier has been reduced via modifying the interface of NCs films or hole transport layer (HTL)
Summary
In the past few decades, colloidal nanocrystals (NCs) have drawn considerable attention due to their solution-processable and low-cost synthesis, high photoluminescence quantum yield (PLQY), and high color purity, as well as tunable emission wavelengths [1,2,3,4] All these superior properties render NCs to offer great potential for light-emitting diodes (LEDs) [5,6,7]. The Auger recombination of charged excitons in NPLs is suppressed by their anisotropic geometry [31,32,33] All of these advantages make aNCs promising for next-generation LEDs. Significant progress has been made for LEDs based on aNCs during the past few years. We will overview the challenges and perspectives of NPL-LEDs
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