Tetragonal CsPbBr nanosheets were obtained by an oriented attachment of orthorhombic CsPbBr nanocubes, involving a lateral shape evolution from octagonal to square. Meanwhile, the experimental results, together with DFT simulation results, indicated that the tetragonal CsPbBr is an indirect bandgap semiconductor that is PL-inactive with a bandgap of 2.979 eV.

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 ...

We report a novel orthogonal lithography fabrication of patterned inorganic perovskite CsPbX 3 (X= Cl, Br, I) quantum dot (QD) arrays which cannot be patterned with traditional approaches. This approach involves a combination of fluorinated polymer and solvent to resolve issues of polar-non-polar solvent constraints thus enabling the fabrication of complex patterns with high optical gain and bright and multicolor emission. We utilized this approach to fabricate high-resolution large-area arrays of microdisk lasers and milticolor (binary-and ternary-emission) pixels. The optical cavity modes of CsPbBr 3 QD microdisk lasers were readily controlled by tuning the disk size, where the mode spacing decreases while the number of modes increases with increasing disk diameter. Finally, we demonstrated the versatility of our approach for the integration of environmentally-sensitive QDs with different emission signatures and composition on the same chip, while achieving high density, highresolution large-area QD arrays with multicolor pixels.

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A derivative-phase CsPb2Br5 is introduced into inorganic perovskite solar cells, which will effectively eliminate interface defects, lower the energy barrier of electron transport layer and suppress the recombination at the interface of hole transport layer in the devices.

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.

Inorganic perovskite materials have demonstrated outstanding performance in the field of photovoltaic devices due to their superior charge carrier transport properties and excellent thermal stability. In particular, the inorganic perovskite derivative phases show special properties in terms of phase stability and optoelectronic application, especially in the phase transition investigation. However, their commercial applications still face challenges due to the large recombination at the interface, resulting in poor efficiency and metastable phases such as iodide perovskite existing in the film. Herein, an all-bromide inorganic perovskite solar cell has been developed by introducing the derivative phases (CsPb 2 Br 5 and Cs 4 PbBr 6 ) to construct gradient bandgap architecture. This graded heterojunction device is realized with a controllable sequential vapor deposition procedure. The valance band maximum elevates gradually with the presence of derivative phases and effectively blocks electrons and boosts the hole extraction efficiency at the counter electrode, which promotes charge separation and reduces the interface recombination. Ultimately, an impressive power conversion efficiency of 10.17% is achieved through a CsPbBr 3 /CsPbBr 3 -CsPb 2 Br 5 /CsPbBr 3 -Cs 4 PbBr 6 architecture strategy with excellent stability above 3000 h (85% of initial performance) in a humid environment (@RH %45%) and 700 h (83% of initial efficiency) under thermal conditions (@ 100 C).

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