The poor stability of CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) has severely impeded their practical applications. Although there are some successful examples on encapsulating multiple CsPbX3 NCs ...into an oxide or polymer matrix, it has remained a serious challenge for the surface modification/encapsulation using oxides or polymers at a single particle level. In this work, monodisperse CsPbX3/SiO2 and CsPbBr3/Ta2O5 Janus nanoparticles were successfully prepared by combining a water-triggered transformation process and a sol–gel method. The CsPbBr3/SiO2 NCs exhibited a photoluminescence quantum yield of 80% and a lifetime of 19.8 ns. The product showed dramatically improved stability against destruction by air, water, and light irradiation. Upon continuous irradiation by intense UV light for 10 h, a film of the CsPbBr3/SiO2 Janus NCs showed only a slight drop (2%) in the PL intensity, while a control sample of unmodified CsPbBr3 NCs displayed a 35% drop. We further highlighted the advantageous features of the CsPbBr3/SiO2 NCs in practical applications by using them as the green light source for the fabrication of a prototype white light emitting diode, and demonstrated a wide color gamut covering up to 138% of the National Television System Committee standard. This work not only provides a novel approach for the surface modification of individual CsPbX3 NCs but also helps to address the challenging stability issue; therefore, it has an important implication toward their practical applications.
All‐inorganic perovskite light‐emitting diodes (LEDs) reveal efficient luminescence with high color purity, but their modest brightness and poor stability are still critical drawbacks. Here, the ...luminescent efficiency and the stability of perovskite LEDs (PeLEDs) are boosted by antisolvent vapor treatment of CsPbBr3 embedded in a dielectric polymer matrix of polyethylene oxide (PEO). A unique method is developed to obtain high quality CsPbBr3 emitting layers with low defects by controlling their grain sizes. CsPbBr3 in PEO matrix is post‐treated with antisolvent of chloroform (CF), leading to microcrystals with a size of ≈5 µm along the in‐plane direction with active emitting composite of 90%. A device based on CF post‐treatment (CsPbBr3‐PEO‐CF) film displays a brightness of up to 51890 cd m−2 with an external quantum efficiency of 4.76%. CsPbBr3‐PEO‐CF PeLED still maintains 82% of its initial efficiency after 80 h continuous operation in ambient air, which indicates relatively good device stability. This work highlights that film quality is not only key to promoting fluorescence in CsPbBr3, but also to achieving higher performance PeLEDs.
Antisolvent vapor treatment of CsPbBr3 films embedded in a dielectric polymer matrix film is proposed, resulting in microcrystal size of ≈5 µm with low defect density. A light‐emitting diode based on composite CsPbBr3 films with this antisolvent vapor treatment displays a brightness of 51890 cd m−2 and an external quantum efficiency of 4.76%.
Organometal halide perovskites (OHP) are promising materials for low-cost, high-efficiency light-emitting diodes. In films with a distribution of two-dimensional OHP nanosheets and small ...three-dimensional nanocrystals, an energy funnel can be realized that concentrates the excitations in highly efficient radiative recombination centers. However, this energy funnel is likely to contain inefficient pathways as the size distribution of nanocrystals, the phase separation between the OHP and the organic phase. Here, we demonstrate that the OHP crystallite distribution and phase separation can be precisely controlled by adding a molecule that suppresses crystallization of the organic phase. We use these improved material properties to achieve OHP light-emitting diodes with an external quantum efficiency of 15.5%. Our results demonstrate that through the addition of judiciously selected molecular additives, sufficient carrier confinement with first-order recombination characteristics, and efficient suppression of non-radiative recombination can be achieved while retaining efficient charge transport characteristics.
Fabricating CsPbX3-based heterostructures has proven to be a feasible way to tune their photophysical properties. Here, we report the successful fabrication of Janus CsPbX3/ZrO2 heterostructure ...nanocrystals (NCs), in which each CsPbX3 NC is partially covered by ZrO2. According to the band alignment, CsPbBr3/ZrO2 and CsPbI3/ZrO2 can be indexed as type I and type II composites, respectively. The type I composites display great enhancement in photoluminescence quantum yield (from 63 to 90%) and photoluminescence lifetime (from 12.9 to 66.1 ns) because of the charge carrier confinement and passivation effect provided by ZrO2. In contrast, the type II composites can be used in photocatalytic reduction of CO2 because electrons and holes are effectively separated and accumulated in ZrO2 and CsPbI3, respectively, under irradiation. Janus CsPbBr3/ZrO2 NCs showed a stability much higher than that of pristine CsPbBr3 against polar solvent treatment. A stable and highly efficient light-emitting device with luminous efficiency up to 55 lm W–1 is fabricated by using CsPbBr3/ZrO2 NCs as the green light source. This work may not only enrich the family of surface-passivated perovskite materials but also provide a good example for the rational design of specific composites in the metal halide perovskite field.
We demonstrate that monodispersed triangular gold nanoplates with high morphological yield (>90%) can be synthesized through a rapid one-pot seedless growth process. The edge length of triangular Au ...nanoplates can be readily tuned between 40 and 120 nm by varying the reaction parameters. Systematic studies reveal that distinct from previous hypothesis that the formation of nanoplates is mainly determined by the selective binding of iodide ions, our results show that iodide ions could have dual functions: it can selectively bind to the Au {111} facets and also selectively remove other less stable shape impurities through oxidative etching by forming tri-iodide ions (I3 –), thus facilitating the formation of nuclei with dominant planar structure. This new synthetic route will not only help to better understand the growth mechanism of triangular gold nanoplates but also promote the research in anisotropic noble metal nanostructures.
We report a novel CsX-stripping mechanism that enables the efficient chemical transformation of nonluminescent Cs4PbX6 (X = Cl, Br, I) nanocrystals (NCs) to highly luminescent CsPbX3 NCs. During the ...transformation, Cs4PbX6 NCs dispersed in a nonpolar solvent are converted into CsPbX3 NCs by stripping CsX through an interfacial reaction with water in a different phase. This process takes advantage of the high solubility of CsX in water as well as the ionic nature and high ion diffusion property of Cs4PbX6 NCs, and produces monodisperse and air-stable CsPbX3 NCs with controllable halide composition, tunable emission wavelength covering the full visible range, narrow emission width, and high photoluminescent quantum yield (up to 75%). An additional advantage is that this is a clean synthesis as Cs4PbX6 NCs are converted into CsPbX3 NCs in the nonpolar phase while the byproduct of CsX is formed in water that could be easily separated from the organic phase. The as-prepared CsPbX3 NCs show enhanced stability against moisture because of the passivated surface. Our finding not only provides a new pathway for the preparation of highly luminescent CsPbX3 NCs but also adds insights into the chemical transformation behavior and stabilization mechanism of these emerging perovskite nanocrystals.
A new generation of photothermal theranostic agents is developed based on PEGylated WS2 nanosheets. Bimodal in vivo CT/photoacoustic imaging reveals strong tumor contrast after either intratumoral or ...intravenous injection of WS2‐PEG. In vivo photothermal treatment is then conducted in a mouse tumor model, achieving excellent therapeutic efficacy with complete ablation of tumors. This work promises further exploration of transition‐metal dichalcogenides for biomedical applications, such as cancer imaging and therapy.
Recently, all‐inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals have drawn much attention because of their outstanding photophysical properties and potential applications. ...In this work, a simple and efficient solvothermal approach to prepare CsPbX3 nanocrystals with tunable and bright photoluminescent (PL) properties, controllable composition, and morphology is presented. CsPbX3 nanocubes are successfully prepared with bright emission high PL quantum yield up to 80% covering the full visible range and narrow emission line widths (from 12 to 36 nm). More importantly, ultrathin CsPbX3 (X = Cl/Br, Br, and Br/I) nanowires (with diameter as small as ≈2.6 nm) can be prepared in a very high morphological yield (almost 100%). A strong quantum confinement effect is observed in the ultrathin nanowires, in which both the absorption and emission peaks shift to shorter wavelength range compared to their bulk bandgap. The reaction parameters, such as temperature and precursors, are varied to investigate the growth process. A white light‐emitting device prototype device with wide color gamut covering up to 120% of the National Television System Committee standard has been demonstrated by using CsPbBr3 nanocrystals as the green light source. The method in this study provides a simple and efficient way to prepare high‐quality CsPbX3 nanocrystals.
A solvothermal method is developed to prepare high‐quality all‐inorganic cesium lead halide (CsPbX3) nanocrystals. Monodisperse CsPbX3 nanocubes and ultrathin CsPbX3 nanowires are prepared. By using the prepared CsPbBr3 nanocrystals as the green light source, a white light‐emitting prototype device with wide color gamut covering up to 120% of the National Television System Committee standard is fabricated.
Photovoltaic (PV) technology offers an economic and sustainable solution to the challenge of increasing energy demand in times of global warming. The world PV market is currently dominated by the ...homo-junction crystalline silicon (c-Si) PV technology based on high temperature diffused p-n junctions, featuring a low power conversion efficiency (PCE). Recent years have seen the successful development of Si heterojunction technologies, boosting the PCE of c-Si solar cells over 26%. This article reviews the development status of high-efficiency c-Si heterojunction solar cells, from the materials to devices, mainly including hydrogenated amorphous silicon (a-Si:H) based silicon heterojunction technology, polycrystalline silicon (poly-Si) based carrier selective passivating contact technology, metal compounds and organic materials based dopant-free passivating contact technology. The application of silicon heterojunction solar cells for ultra-high efficiency perovskite/c-Si and III-V/c-Si tandem devices is also reviewed. In the last, the perspective, challenge and potential solutions of silicon heterojunction solar cells, as well as the tandem solar cells are discussed.
Abstract
Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. ...However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.
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