All-Inorganic Perovskite Nanocrystals with a Stellar Set of Stabilities and Their Use in White Light-Emitting Diodes

Abstract

We report a simple, robust, and inexpensive strategy to enable all-inorganic CsPbX₃ perovskite nanocrystals (NCs) with a set of markedly improved stabilities, that is, water stability, compositional stability, phase stability, and phase segregation stability via impregnating them in solid organic salt matrices (i.e., metal stearate; MSt). In addition to acting as matrices, MSt also functions as the ligand bound to the surface of CsPbX₃ NCs, thereby eliminating the potential damage of NCs commonly encountered during purification as in copious past work. Quite intriguingly, the resulting CsPbX₃-MSt nanocomposites display an outstanding suite of stabilities. First, they retain high emission in the presence of water because of the insolubility of MSt in water, signifying their excellent water stability. Second, anion exchange between CsPbBr₃-MSt and CsPbI₃-MSt nanocomposites is greatly suppressed. This can be ascribed to the efficient coating of MSt, thus effectively isolating the contact between CsPbBr₃ and CsPbI₃ NCs, reflecting notable compositional stability. Third, remarkably, after being impregnated by MSt, the resulting CsPbI₃-MSt nanocomposites sustain the cubic phase of CsPbI₃ and high emission, manifesting the strikingly improved phase stability. Finally, phase segregation of CsPbBr_1.5I_1.5 NCs is arrested via the MSt encapsulation (i.e., no formation of the respective CsPbBr₃ and CsPbI₃), thus rendering pure and stable photoluminescence (i.e., demonstration of phase segregation stability). Notably, when assembled into typical white light-emitting diode architecture, CsPbBr_1.5I_1.5-MSt nanocomposites exhibit appealing performance, including a high color rendering index ( R_a) and a low color temperature ( T_c). As such, the judicious encapsulation of perovskite NCs into organic salts represents a facile and robust strategy for creating high-quality solid-state luminophores for use in optoelectronic devices.