Cesium Lead Bromide Nanocrystals Research Articles

Photoluminescence and photovoltaic properties of cesium lead bromide nanocrystals with linoleic acid ligand

Cesium lead bromide (CsPbBr3) nanocrystals (NCs) were synthesized using the ligand-assisted reprecipitation (LARP) method, with linoleic acid (LA) and oleylamine (OlAm) as ligands. The crystal structures of the samples depend on the ligand used in the synthesis. Sample-1, with LA-OlAm as the ligand, showed an orthorhombic crystal structure, whereas Sample-2, with OlAm only, showed a tetragonal crystal structure. These samples exhibited slightly different photoluminescence (PL) characteristics, where the PL peak of Sample-1 appeared at 521.4 nm, whereas the PL peak of Sample-2 appeared at 524.1 nm. Sample-1 showed brighter PL than that of Sample-2. These differences are strongly related to their crystal structures and degree of crystallization, which is also evident from the differences in the chemical states of the Br and Pb ions on the NCs surface, as depicted by the X-Ray Photoelectron Spectroscopy (XPS) spectra. In addition, despite exhibiting PL characteristics, these CsPbBr3 NCs also exhibit photovoltaic properties.

Short-branched alkyl sulfobetaine-passivated CsPbBr3 nanocrystals for efficient green light emitting diodes.

Inorganic cesium lead bromide nanocrystals (CsPbBr3 NCs) hold promising prospects for high performance green light-emitting diodes (LEDs) due to their exceptional color purity and high luminescence efficiency. However, the common ligands employed for passivating these indispensable NCs, such as long-chain organic ligands like oleic acid and oleylamine (OA/OAm), display highly dynamic binding and electronic insulating issues, thereby resulting in a low efficiency of the as-fabricated LEDs. Herein, we report a new zwitterionic short-branched alkyl sulfobetaine ligand, namely trioctyl(propyl-3-sulfonate) ammonium betaine (TOAB), to in situ passivate CsPbBr3 NCs via a feasible one-step solution synthesis, enabling efficiency improvement of CsPbBr3 NC-based LEDs. The zwitterionic TOAB ligand not only strengthened the surface passivation of CsPbBr3 NCs with a high photoluminescence quantum yield (PLQY) of 97%, but also enhanced the carrier transport in the fabricated CsPbBr3 NC thin films due to the short-branched alkyl design. Consequently, CsPbBr3 NCs passivated with TOAB achieved a green LED with an external quantum efficiency (EQE) of 7.3% and a maximum luminance of 5716 cd m-2, surpassing those of LEDs based on insulating long-chain ligand-passivated NCs. Our work provides an effective surface passivation ligand design to enhance the performance of CsPbBr3 NC-based LEDs.

Effects of Perfluorodecanoic Acid on the Photostability and Self-Recovery of Cesium Lead Bromide Nanocrystals

Photoinduced desorption of surface ligands causes photodegradation of nanophosphors due to enhanced non-radiative relaxation, which is attributed to generated surface defects. We previously reported the self-recovery of photodegraded CsPbBr3 nanocrystals (NCs) and revealed that its mechanism can be attributed to readsorption of the desorbed surface ligands. Thus, using different surface ligands would change the photodegradation and subsequent self-recovery behaviors. Accordingly, in the present work, perfluorodecanoic acid (PFDA) was added to pre-synthesized CsPbBr3 NCs modified with oleic acid and oleylamine to evaluate its effects on photodegradation and subsequent self-recovery. The as-prepared NCs (OA-NCs) and PFDA-modified NCs (PFDA-NCs) were dispersed in nanocomposite ethylene-vinyl acetate resin films to suppress concentration quenching. OA-NCs showed monotonical photoluminescence (PL) decrease under blue excitation light and self-recovery during subsequent dark storage. In contrast, the PFDA-NCs exhibited temporary PL enhancement under excitation irradiation. The photo-activation is attributed to optimization of the adsorption states of the surface ligands in the early stage, while the influence of photodegradation due to ligand desorption becomes dominant later. However, increased PFDA modification prevented self-recovery, indicating that desorbed PFDA may be resistant to readsorption on the NC surface.

Photoinduced electron transfer across the polymer-capped CsPbBr3 interface in a polar medium.

In-situ polymer capping of cesium lead bromide (CsPbBr3) nanocrystals with polymethyl acrylate is an effective approach to improve the colloidal stability in the polar medium and thus extends their use in photocatalysis. The photoinduced electron transfer properties of polymethyl acrylate (PMA)-capped CsPbBr3 nanocrystals have been probed using surface-bound viologen molecules with different alkyl chains as electron acceptors. The apparent association constant (Kapp) obtained for the binding of viologen molecules with PMA-capped CsPbBr3 was 2.3 × 107 M-1, which is an order of magnitude greater than that obtained with oleic acid/oleylamine-capped CsPbBr3. Although the length of the alkyl chain of the viologen molecule did not show any impact on the electron transfer rate constant, it influenced the charge separation efficiency and net electron transfer quantum yield. Viologen moieties with a shorter alkyl chain length exhibited a charge separation efficiency of 72% compared with 50% for the longer chain alkyl chain length viologens. Implications of polymer-capped CsPbBr3 perovskite nanocrystals for carrying out photocatalytic reduction in the polar medium are discussed.

Elastic Phonon Scattering Dominates Dephasing in Weakly Confined Cesium Lead Bromide Nanocrystals at Cryogenic Temperatures.

Cesium lead halide perovskite nanocrystals (PNCs) have emerged as a potential next-generation single quantum emitter (QE) material for quantum optics and quantum information science. Optical dephasing processes at cryogenic temperatures are critical to the quality of a QE, making a mechanistic understanding of coherence losses of fundamental interest. We use photon-correlation Fourier spectroscopy (PCFS) to obtain a lower bound to the optical coherence times of single PNCs as a function of temperature. We find that 20 nm CsPbBr3 PNCs emit nearly exclusively into a narrow zero-phonon line from 4 to 13 K. Remarkably, no spectral diffusion is observed at time scales of 10 μs to 5 ms. Our results suggest that exciton dephasing in this temperature range is dominated by elastic scattering from phonon modes with characteristic frequencies of 1-3 meV, while inelastic scattering is minimal due to weak exciton-phonon coupling.

Optical and photoelectrical properties of low-concentration-Mn-doped CsPbBr3 nanocrystals

Doping of cesium lead bromide (CsPbBr3) perovskite nanocrystals offers effective control of their optical and optoelectrical properties, leading to possibilities of several new applications. Herein, cesium lead bromide perovskite nanocrystals are synthesized with doping of a low concentration of manganese (Mn) into the perovskite lattice using manganese (II) chloride (MnCl2) as a precursor. The shift in X-ray diffraction peaks toward higher angles indicates that manganese as a dopant is present inside the cesium lead bromide lattice. A change in the manganese (II) chloride precursor concentration from 5 to 10 mmol results in an increment in the atomic percentage of manganese from 0.3 to 0.5% in the cesium lead bromide crystal. Doping of a low concentration of manganese (0.3 at.%) into cesium lead bromide results in enhancement of green emission, while doping with a higher concentration of manganese (0.5 at.%) results in blue emission. The band gap of cesium lead bromide nanocrystals increases from 2.31 to 2.53 eV with an increase in the concentration of manganese. The dark and photoelectrical conductivity of cesium lead bromide nanocrystals is improved in the case of doping with a low concentration (0.3 at.%) of manganese. The ratio of photocurrent against dark current is found to be ∼182 in manganese-doped cesium lead bromide crystal film as compared with ∼101 for undoped cesium lead bromide crystal film. Doping with a low concentration of manganese improves the overall electrical and photoelectrical conductivity of cesium lead bromide perovskite nanocrystals.

Engineering Water Stable Perovskite and Plasmonic‐Perovskite Nanocomposites: A Step toward Unleashing the True Potential of Perovskite Catalysis

AbstractDespite garnering so much research interest, the potential technological developments of perovskites are limited due to the instability of perovskites in polar solvents. Here, it is discovered that upon exposure to ethanol, the initial cubic cesium lead bromide nanocrystals (CsPbBr3 NCs) undergo a phase transformation from the cubic phase to the orthorhombic phase. Further exposure of the orthorhombic phase to water leads to the formation of CsPbBr3 perovskite nanoaggregates, which shows higher stability in water compared to pristine CsPbBr3 NCs. A systematic investigation of the interfaces using various spectroscopic techniques demonstrating the self‐assembly process and phase transformation is presented. The increased stability of ethanol‐treated CsPbBr3 NCs is attributed to the ethoxide ions adsorption on the CsPbBr3 interface, owing to strong affinity of alkoxide ions to Pb2+. Effective surface passivation leads to enhanced charge‐carrier separation, a prerequisite to an effective photocatalyst. Ethoxide‐stabilized CsPbBr3 in water is utilized to reduce Au3+ to Au0 to synthesize water‐stable Au‐CsPbBr3 nanocomposites. The formation of hybrid plasmonic metal‐perovskites nanocomposite influences the perovskite's excited state charge carrier dynamics. This opens the possibilities of utilizing the synergistic effects of the light‐harvesting properties of plasmonic nanomaterials with the catalytic attributes of perovskite materials and controlling the interface properties by tuning plasmon–exciton coupling.

Cesium Lead Bromide Nanocrystals: Synthesis, Modification, and Application to O2 Sensing.

The fluorescence intensity of inorganic CsPbBr3 (CPB) perovskite nanocrystals (NCs) decreases in the presence of O2. In this study, we synthesized CPB NCs with various shapes and sizes for use as optical gas sensing materials. We fabricated O2 gas sensors from the various CPB NCs on several porous and nonporous substrates and examined the effects of the NC shapes and aggregate sizes and the substrate pore size on the device response. Our sensor fabricated from CPB nanocrystals on a porous substrate exhibited the highest response; the porous substrate allowed the rapid diffusion of O2 such that the NC surface was exposed effectively to the gas. Thus, the interfacial interaction between NC surfaces and substrates is a critical factor for consideration when preparing gas sensors with a high response.

The Fabrication of Cesium Lead Bromide-Coated Cellulose Nanocomposites and Their Effect on the Detection of Nitrogen Gas.

In this work, we fabricate cesium lead bromide nanofibers (CsPbBr3 NFs) via the attachment of cesium lead bromide nanocrystals (CsPbBr3 NCs) on the surface of electrospun cellulose nanofibers (CNFs) and employ them in a sensor to effectively detect gaseous nitrogen. The CsPbBr3 NFs are produced initially by producing CsPbBr3 NCs through hot injection and dispersing on hexane, followed by dipping CNFs and ultrasonicate for 1 h. Morphological characterization through visual, SEM and TEM image, and crystalline structure analysis by XRD and FT-IR analysis of CsPbBr3 NFs and NCs show similar spectra except for PL due to unavoidable damage during the ultrasonication. Gaseous nitrogen is subsequently detected using the photoluminescence (PL) property of CsPbBr3 NFs, in which the PL intensity dramatically decreases under various flow rate. Therefore, we believe that the proposed CsPbBr3 NFs show significant promise for use in detection sensors in various industrial field and decrease the potential of fatal damage to workers due to suffocation.

PVDF-directed synthesis, stability and anion exchange of cesium lead bromide nanocrystals

Photoluminescent perovskite nanocrystals are mostly used along with base materials such as polymers for material processing and large-scale production purpose. However, the role of polymer in crystal structure engineering and thereby dictating the emission properties of lead halide perovskite nanocrystals has been poorly understood. First, we have developed a polymer-directed antisolvent method for synthesis of halide perovskite crystals at room temperature and observed that the thermodynamic stabilities of crystals drive the formation of perovskite composite crystal of orthorhombic Cs4PbBr6 and monoclinic CsPbBr3. Surprisingly, hydrophobic polyvinylidene fluoride (PVDF) can reduce the size of perovskite crystals to nano dimensions even at room temperature. On the other hand, perovskite nanocrystals, CsPbBr3 synthesized by modified hot-injection method undergo rapid encapsulation in PVDF matrices. The size of the encapsulated nanocrystal in PVDF matrices ranges in 88 ± 32 nm. We have illustrated that there are three types of radiative recombination predominantly operative in nanocrystals-doped polymer- (i) surface defect caused radiative recombination (0.6–3 ns), (ii) exciton recombination (3–15 ns), and (iii) shallow trap assisted recombination (10–50 ns). The interface created at nanocrystal and polymer plays a decisive role in populating the shallow trap states in perovskite-polymer nanocomposite. These nanocomposites undergo fast halide exchange in aqueous hydroiodic acid solution and possess remarkable enhancement of water-/photo-stability. This research would pave way for their greater use in hydrogen production and light-emitting devices.

Generation of Free Carriers in MoSe2 Monolayers Via Energy Transfer from CsPbBr3 Nanocrystals

AbstractTransition metal dichalcogenide (TMDCs) monolayers make an excellent component in optoelectronic devices such as photodetectors and phototransistors. Selenide‐based TMDCs, specifically molybdenum diselenide (MoSe2) monolayers with low defect densities, show much faster photoresponses compared to their sulfide counterpart. However, the typically low absorption of the atomically thin MoSe2 monolayer and high exciton binding energy limit the photogeneration of charge carriers. Yet, integration of light‐harvesting materials with TMDCs can produce increased photocurrents via energy transfer. In this article, it is demonstrated that the interaction of cesium lead bromide (CsPbBr3) nanocrystals with MoSe2 monolayers results into an energy transfer efficiency of over 86%, as ascertained from the quenching and decay dynamics of the CsPbBr3 nanocrystals emission. Notably, the increase in the MoSe2 monolayer emission in the heterostructure accounts only for 33% of the transferred energy. It is found that part of the excess energy generates directly free carriers in the MoSe2 monolayer, as a result of the transfer of energy into the exciton continuum. The efficiency of the heterostructure via enhanced photocurrents with respect to the single material unit is proven. These results demonstrate a viable route to overcome the high exciton binding energy typical for TMDCs, as such having an impact on optoelectronic processes that rely on efficient exciton dissociation.

Laser-Induced Morphological and Structural Changes of Cesium Lead Bromide Nanocrystals.

Metal halide perovskite nanocrystals, an emerging class of materials for advanced photonic and optoelectronic applications, are mainly fabricated with colloidal chemistry routes. On the quest for new properties according to application needs, new perovskite systems of various morphologies and levels of doping and alloying have been developed, often also involving post-synthesis reactions. Recently, laser irradiation in liquids has been utilized as a fast method to synthesize or transform materials and interesting laser-induced transformations on nanocrystals were induced. These studies in general have been limited to small nanocrystals (~15 nm). In the case of halide perovskites, fragmentation or anion exchange have been observed in such laser-based processes, but no crystal structure transformations were actually observed or deliberately studied. Nanocrystals are more sensitive to light exposure compared to the corresponding bulk crystals. Additional factors, such as size, morphology, the presence of impurities, and others, can intricately affect the photon absorption and heat dissipation in nanocrystal suspensions during laser irradiation. All these factors can play an important role in the final morphologies and in the time required for these transformations to unfold. In the present work, we have employed a 513 nm femtosecond (fs) laser to induce different transformations in large nanocrystals, in which two phases coexist in the same particle (Cs4PbBr6/CsPbBr3 nanohexagons of ~100 nm), dispersed in dichlorobenzene. These transformations include: (i) the exfoliation of the primary nanohexagons and partial anion exchange; (ii) fragmentation in smaller nanocubes and partial anion exchange; (iii) side-by-side-oriented attachment, fusion, and formation of nanoplatelets and complete anion exchange; (iv) side-by-side attachment, fusion, and formation of nanosheets. Partial or complete Br-Cl anion exchange in the above transformations was triggered by the partial degradation of dichlorobenzene. In addition to the detailed analysis of the various nanocrystal morphologies observed in the various transformations, the structure–photoluminescence relationships for the different samples were analyzed and discussed.

Impact of Zn-doping on the composition, stability, luminescence properties of silica coated all-inorganic cesium lead bromide nanocrystals and their biocompatibility

Cesium lead halide (CsPbX3: X = I, Br, Cl) nanocrystals (NCs) are believed to be potential candidates for bioimaging applications. However, their low structural stability against polar solvents remains as a major limitation. To improve the NCs stability and maintain high emission intensity, we synthesized silica coated Zn-doped core@shell perovskite NCs via modified ligand assisted reprecipitation (LARP) synthetic method under relatively high humid condition. We systemically varied the composition inside the perovskite structure and then studied their photophysical properties and stability. Interestingly, the Zn-doping amount controls the ratio of CsPbBr3 to Cs4PbBr6 perovskites inside the core and also facilitates the growth of (OA)2PbBr4 shell, enables overall increase in NCs emission intensity and stability. We observed green color emission from these NCs in the spectral range of 494-506 nm with a maximum photoluminescence quantum yield (PLQY) up to 88%. The optimized Zn-doped NCs exhibited nearly four times better water stability compared to the bare NCs and retain emission properties for several months even in highly polar solvents. Finally, we performed biocompatibility test of the NCs generated on biological samples and hydroponics test in a gardenia leaf for their potential bioimaging applications.

Water‐Durable Cesium Lead Halide Perovskite Nanocrystals Passivated with a Cationic Gemini Surfactant

AbstractChemical states of perovskite nanocrystal surfaces are vital to withdraw their intrinsic optoelectronic nature and maintain the colloidal stability. This study reports that the cationic gemini surfactant alkanediyl‐α,ω‐bis(dodecyldimethylammonium bromide) “12‐n‐12” dramatically improved the luminescence properties and chemical stability of cesium lead bromide nanocrystals (CsPbBr3 NCs). Dispersion stability of CsPbBr3 NCs passivated with 12‐n‐12 (n = 3−7) is enhanced with the methylene spacer length, their dynamic light scattering studies ensure that the gemini ligands with more than the pentyl methylene spacer exhibit mono dispersion of NCs. Nuclear magnetic resonance and X‐ray photoemission spectroscopy studies reveal that 12‐n‐12 is bound to the surfaces of CsPbBr3 NCs with a density of 0.74−1.06 nm−2 which is less than half the didodecyldimethylammonium bromide (DDAB) ligand density. Nevertheless, CsPbBr3 NCs with the 12‐n‐12 shell exhibit a high photoluminescence quantum yield equal to that of DDAB. Furthermore, the 12‐n‐12 shell demonstrates remarkably excellent luminescence stability when the NC solution is exposed to water. Hence, 12‐n‐12 is a promising candidate to substitute the conventional ligands.

Cesium Lead Bromide Nanocrystals: Synthesis, Modification, and Application to O2 Sensing

Cesium Lead Bromide Nanocrystals: Synthesis, Modification, and Application to O2 Sensing

Synthesis of highly stable double-coated Zn-doped cesium lead bromide nanocrystals for indium ion detection in water

Double-coated CsPbBr3@SiO2@PVP perovskite NCs exhibit higher luminous intensity and better structural stability than those without PVP, enabling indium ion detection in water.

Visual colorimetric detection of ammonia under gaseous and aqueous state: Approach on cesium lead bromide perovskite-loaded porous electrospun nanofibers

In this work, we fabricate porous cesium lead bromide nanofibers (CsPbBr3 NFs) via electrospinning and employ them in a sensor to effectively detect both gaseous and aqueous ammonia. The CsPbBr3 NFs are produced by first mixing cesium lead bromide nanocrystals (CsPbBr3 NCs) with polystyrene (PS), followed by solidifying the mixture into NFs using electrospinning. Porous NFs are modified using the volatile solvent toluene, which is volatilized during the electrospinning process. The applicability of the proposed CsPbBr3 NFs for use under various environmental conditions is verified by analyzing their stability in response to changes in temperature, moisture level and pH, which are critical drawbacks of CsPbBr3 NCs. Gaseous ammonia (9mgL−1) in an N2 carrier is subsequently detected using the photoluminescence (PL) properties of the CsPbBr3 NFs. In addition, an ammonia concentration of 100.0mgL−1 in an aqueous solution can be detected using the PL intensity. Therefore, we believe that the proposed CsPbBr3 NFs show significant promise for use in detection sensors to assess the extent of food decay, allowing customers to purchase fresh agricultural products more safely.

Detection of Halomethanes Using Cesium Lead Halide Perovskite Nanocrystals.

The extensive use of halomethanes (CH3X, X = F, Cl, Br, I) as refrigerants, propellants, and pesticides has drawn serious concern due to their adverse biological and atmospheric impact. However, there are currently no portable rapid and accurate monitoring systems for their detection. This work introduces an approach for the selective and sensitive detection of halomethanes using photoluminescence spectral shifts in cesium lead halide perovskite nanocrystals. Focusing on iodomethane (CH3I) as a model system, it is shown that cesium lead bromide (CsPbBr3) nanocrystals can undergo rapid (<5 s) halide exchange, but only after exposure to oleylamine to induce nucleophilic substitution of the CH3I and release the iodide species. The extent of the halide exchange is directly dependent on the CH3I concentration, with the photoluminescence emission of the CsPbBr3 nanocrystals exhibiting a redshift of more than 150 nm upon the addition of 10 ppmv of CH3I. This represents the widest detection range and the highest sensitivity to the detection of halomethanes using a low-cost and portable approach reported to date. Furthermore, inherent selectivity for halomethanes compared to other organohalide analogues is achieved through the dramatic differences in their alkylation reactivity.

The impact of cation and anion pairing in ionic salts on surface defect passivation in cesium lead bromide nanocrystals

Binding strength between cation and anion in a ligand has a major impact on their charge trap passivation efficacy.

Irreversibility in Anion Exchange Between Cesium Lead Bromide and Iodide Nanocrystals Imaged by Single-Particle Fluorescence

Anion exchange is a powerful method to tune the emission wavelength of perovskite CsPbX3 (X = Cl, Br, or I) nanocrystals across the visible spectrum. CsPbX3 nanocrystals can possess a number of cry...