Core/Shell Perovskite Nanocrystals: Synthesis of Highly Efficient and Environmentally Stable FAPbBr3/CsPbBr3 for LED Applications

Lead halide perovskite nanocrystals (PeNCs) are promising materials for applications in optoelectronics. However, their environmental instability remains to be addressed to enable their advancement into industry. Here the development of a novel synthesis method is reported for monodispersed PeNCs coated with all inorganic shell of cesium lead bromide (CsPbBr₃) grown epitaxially on the surface of formamidinium lead bromide (FAPbBr₃) NCs. The formed FAPbBr₃/CsPbBr₃ NCs have photoluminescence in the visible range 460–560 nm with narrow emission linewidth (20 nm) and high optical quantum yield, photoluminescence quantum yield (PLQY) up to 93%. The core/shell perovskites have enhanced optical stability under ambient conditions (70 d) and under ultraviolet radiation (50 h). The enhanced properties are attributed to overgrowth of FAPbBr₃ with all‐inorganic CsPbBr₃ shell, which acts as a protective layer and enables effective passivation of the surface defects. The use of these green‐emitting core/shell FAPbBr₃/CsPbBr₃ NCs is demonstrated in light‐emitting diodes (LEDs) and significant enhancement of their performance is achieved compared to core only FAPbBr₃‐LEDs. The maximum current efficiency observed in core/shell NC LED is 19.75 cd A^‐1 and the external quantum efficiency of 8.1%, which are approximately four times and approximately eight times higher, respectively, compared to core‐only devices.     

2D Ruddlesden–Popper Perovskite Nanoplate Based Deep‐Blue Light‐Emitting Diodes for Light Communication

Ruddlesden–Popper perovskite, (PEA)₂PbBr₄ (PEA = C₈H₉NH₃), is a steady and inexpensive material with a broad bandgap and a narrow‐band emission. These features make it a potential candidate for deep‐blue light‐emitting diodes (LEDs). However, due to the weak exciton binding energy, LEDs based on the perovskite thin films usually possess a very low external quantum efficiency (EQE) of <0.03%. Here, for the first time, the construction of high‐performance deep‐blue LEDs based on 2D (PEA)₂PbBr₄ nanoplates (NPs) is demonstrated. The as‐fabricated (PEA)₂PbBr₄ NPs film shows a deep‐blue emission at 410 nm with excellent stability under ambient conditions. Impressively, LEDs based on the (PEA)₂PbBr₄ NPs film deliver a bright deep‐blue emission with a maximum luminance of 147.6 cd m^?2 and a high EQE up to 0.31%, which represents the most efficient and brightest perovskite LEDs operating at deep‐blue wavelengths. Furthermore, the LEDs retain over 80% of their efficiencies for over 1350 min under ≈60% relative humidity. The steady and bright deep‐blue LEDs can be used as an excitation light source to realize white light emission, which shows the potential for light communication. The work provides scope for developing perovskite into efficient and deep‐blue LEDs for low‐cost light source and light communication.     

Hierarchical Self‐Assembly of a Dandelion‐Like Supramolecular Polymer into Nanotubes for use as Highly Efficient Aqueous Light‐Harvesting Systems

A dandelion‐like supramolecular polymer (DSP) with a “sphere‐star‐parachute” topological structure consisting of a spherical hyperbranched core and many parachute‐like arms is constructed by the non‐covalent host–guest coupling between a cyclodextrin‐endcapped hyperbranched multi‐arm copolymer (host) and many functionalized adamantanes with each having three alkyl chain arms (guests). The obtained DSPs can further self‐assemble into nanotubes in water in a hierarchical way from vesicles to nanotubes through sequential vesicle aggregation and fusion steps. The nanotubes have a bilayer structure consisting of multiple “hydrophobic‐hyperbranched‐hydrophilic” layers. Such a structure is very useful for constructing a chlorosome‐like artificial aqueous light‐harvesting system, as demonstrated here, via the incorporation of hydrophobic 4‐(2‐hydroxyethylamino)‐7‐nitro‐2,1,3‐benzoxadiazole as donors inside the hyperbranched cores of the nanotubes and the hydrophilic Rhodamine B as the acceptors immobilized on the nanotube surfaces. This as‐prepared nanotube light harvesting system demonstrates unexpectedly high energy transfer efficiency (above 90%) in water. This extends supramolecular polymers with more complex topological structure, special self‐assembly behavior, and new functionality.