Doping and ion substitution in colloidal metal halide perovskite nanocrystals and their implication on compositions, properties, and applications.

ganic CsPbX 3 QDs possess narrow full width at half maximum (FWHM) of emission (as small as 12 nm) and excellent quantum yield (QY: 50-90%). [1,8] They have a Bohr diameter up to 12 nm, [1] exhibiting a size-tunable bandgap in the visible region. It is also notable that the exchange of halide ions (Cl − , Br − , and I − ) in as-synthesized perovskite QDs is highly effective, rendering easy and rapid access to a wide range of perovskite QDs with tunable absorption and photoluminescence (PL) spectra. [1] In spite of significant advances in perovskite research noted above, a key to the success of perovskite-based materials and devices is the stability of perovskites as they are susceptible to decomposition due to their ionic crystal nature. [7,9] Recently, several methods including coating with alumina by atomic layer deposition, [10] partial coating with SiO 2 via sol-gel process, [11] physical mixing with hydrophobic polymers, [12] and encapsulation within mesoporous silica [7] or polymer beads [13] have proven to be effective in improving stability in polar and ambient environments. However, nearly all approaches described above for stability enhancement result in nanocomposites with multiple perovskite QDs encapsulated in microscopic protective matrices. These microscale nanocomposites may be disadvantageous for biomedical applications where cellular uptake is more feasible for smaller nanoscopic particles, [14] or LEDs where the processing of nanoscopic luminescent particles often leads to low scattering loss, higher loading and packing density, and thus film uniformity. [11] Clearly, the ability to deliberately and reliably improve the stability of perovskite QDs (e.g., against humidity and polar solvents) while retaining their individual nanometer size represents a critical step that underpins future advances in optoelectronic and biological applications.Herein, we report a general and robust strategy by capitalizing on judiciously designed amphiphilic star-like diblock copolymers with well-controlled molecular weight and low polydispersity of each block as molecularly engineered nanoreactors to craft uniform perovskite QDs. Remarkably, these QDs simultaneously possess precisely tunable dimensions Instability of perovskite quantum dots (QDs) toward humidity remains one of the major obstacles for their long-term use in optoelectronic devices. Herein, a general amphiphilic star-like block copolymer nanoreactor strategy for in situ crafting a set of hairy perovskite QDs with precisely tunable size and exceptionally high water and colloidal stabilities is presented. The selective partition of precursors within the compartment occupied by inner hydrophilic blocks of star-like diblock copolymers imparts in situ formation of robust hairy perovskite QDs permanently ligated by outer hydrophobic blocks via coprecipitation in nonpolar solvent. These size-and compositiontunable perovskite QDs reveal impressive water and colloidal stabilities as the surface of QDs is intimately and permanently ligated by a layer of outer ...

The past few years have witnessed rapid advances in the synthesis of high-quality perovskite nanocrystals (PNCs). However, despite the impressive developments, the stability of PNCs remains a substantial challenge. The ability to reliably improve stability of PNCs while retaining their individual nanometer size represents a critical step that underpins future advances in optoelectronic applications. Here, we report an unconventional strategy for crafting dual-shelled PNCs (i.e., polymer-ligated perovskite/SiO2 core/shell NCs) with exquisite control over dimensions, surface chemistry, and stabilities. In stark contrast to conventional methods, our strategy relies on capitalizing on judiciously designed star-like copolymers as nanoreactors to render the growth of core/shell NCs with controlled yet tunable perovskite core diameter, SiO2 shell thickness, and surface chemistry. Consequently, the resulting polymer-tethered perovskite/SiO2 core/shell NCs display concurrently a stellar set of substantially improved stabilities (i.e., colloidal stability, chemical composition stability, photostability, water stability), while having appealing solution processability, which are unattainable by conventional methods.

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 CsPbBr1.5I1.5 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, CsPbBr1.5I1.5–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.

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