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.

A trade‐off between open‐circuit voltage (V OC) and high short‐circuit (J SC) becomes one of the most vital problems limiting further improvement in polymer solar cells' (PSCs) efficiency. In this work, two asymmetric polymer donors PBDT‐F‐2TC and PBDT‐SF‐2TC are designed and synthesized. When blended with a state‐of‐the‐art acceptor IT‐4F with low lowest‐unoccupied molecular orbital level, simultaneously high V OC (up to 0.94 V) and J SC (up to 20.73 mA cm−2) are obtained for both copolymers. Note that the V OC value of 0.94 V is the highest value of PSCs based on IT‐4F reported so far. The simultaneously improved V OC and J SC in resulting devices are discovered from the deep highest‐occupied molecular orbital levels (−5.5 to −5.7 eV) and the hyperchromic effect of the polymers, the small driving force, and the small energy loss during the charge transfer, due to the synergistic effect of asymmetric carboxylate unit and fluorine/sulfur atoms. More importantly, thanks to the asymmetric 2TC, both PBDT‐F‐2TC‐ and PBDT‐SF‐2TC‐based PSCs can be successfully processed by non‐halogenated solvent 1,2,4‐trimethylbenzene (TMB) to yield device efficiencies of 10.29% and 10.39%, respectively, which are the maximum values for non‐fullerene PSCs fabricated using the eco‐friendly solvent TMB.

Formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) have been demonstrated to exhibit ideal ultrapure green luminescence at 530 nm and to hold great potential in light-emitting diodes, by potentially overcoming the difficulties facing cesium lead bromide (CsPbBr3) NCs. However, compared to all-inorganic lead halide perovskite NCs, organic–inorganic hybrid FAPbBr3 NCs are sensitive to moisture, oxygen, and heat due to their intrinsic instability caused by the organic cations (FA+). Herein, we present an epitaxial growth method for the overgrowth of a large-band-gap cesium lead halide (Cs4PbBr6) shell on the surface of FAPbBr3 NCs. The resulting core/shell NCs show a near-unity photoluminescence quantum yield (PLQY) of 97.1%, the emission with full width at half-maxima of 88 meV, and long-term environmental stability. The introduction of Cs+ into FAPbBr3 NCs can inhibit the migration of FA+ and suppress the phase transformation from cubic phase to tetragonal phase at 60 °C. Furthermore, the existence of shell can provide stronger exciton confinement and improve the thermal stability of FAPbBr3 NCs. The core/shell perovskite NCs developed in this study have the advantages of high PLQY and good stability and may contribute to the field of light-emitting diodes (LEDs).

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