Conventional organic light‐emitting devices without an encapsulation layer are susceptible to degradation when exposed to air, so realization of air‐stable intrinsically‐stretchable display is a great challenge because the protection of the devices against penetration of moisture and oxygen is even more difficult under stretching. An air‐stable intrinsically‐stretchable display that is composed of an intrinsically‐stretchable electroluminescent device (SELD) integrated with a stretchable color‐conversion layer (SCCL) that contains perovskite nanocrystals (PeNCs) is proposed. PeNCs normally decay when exposed to air, but they become resistant to this decay when dispersed in a stretchable elastomer matrix; this change is a result of a compatibility between capping ligands and the elastomer matrix. Counterintuitively, the moisture can efficiently passivate surface defects of PeNCs, to yield significant increases in both photoluminescence intensity and lifetime. A display that can be stretched up to 180% is demonstrated; it is composed of an air‐stable SCCL that down‐converts the SELD’s blue emission and reemits it as green. The work elucidates the basis of moisture‐assisted surface passivation of PeNCs and provides a promising strategy to improve the quantum efficiency of PeNCs with the aid of moisture, which allows PeNCs to be applied for air‐stable stretchable displays.
Metal halide perovskites (MHPs) are promising light emitters because they have high color purity, high charge‐carrier mobility, comparable energy levels with organic semiconductors, and the possibility of diverse crystal forms and various crystal formation methods. Since the first report of MHP light‐emitting diodes (PeLEDs) in 2014, many researchers have devoted efforts to increase the luminescence efficiencies of MHPs in various crystal forms, and achieved dramatically improved photoluminescence quantum efficiency of >90% in MHP emitters and external quantum efficiency of ≈14.36% in PeLEDs. Here, the recent progress regarding PeLEDs is reviewed by categorizing MHPs into three types: polycrystalline bulk films, colloidal nanocrystals, and single crystals. The main focus is on photophysical properties, crystallization methods, and mechanisms of various crystal formation, and applications to PeLEDs. Future research directions are also suggested and an outlook for MHP emitters and PeLEDs is given.
Existing gels are mostly polar, whose nature limits their role in soft devices. The intermolecular interactions of nonpolar polymer-liquid system are typically weak, which makes the gel brittle. Here we report highly soft and transparent nonpolar organogels. Even though their elements are only carbon and hydrogen, their elastic modulus, transparency, and stretchability are comparable to common soft hydrogels. A key strategy is introducing aromatic interaction into the polymer-solvent system, resulting in a high swelling ratio that enables efficient plasticization of the polymer networks. As a proof of applicability, soft perovskite nanocomposites are synthesized, where the nonpolar environment of organogels enables stable formation and preservation of highly concentrated perovskite nanocrystals, showing high photoluminescence efficiency (~99.8%) after water-exposure and environmental stabilities against air, water, acid, base, heat, light, and mechanical deformation. Their superb properties enable the demonstration of soft electroluminescent devices that stably emit bright and pure green light under diverse deformations.
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