CsPbBr3 Perovskite Nanocrystals Research Articles

Elucidating the photophysics behind the stimulated emission processes in CsPbBr3 nanocrystals films

Thanks to their excellent photoluminescence quantum yields, their facile and low-cost production, and their processing versatility, CsPbBr3 perovskite nanocrystals (NCs) stand out as excellent candidates to implement light-emitting devices. Elucidating their stimulated emission mechanisms is fundamental to achieve much more efficient and versatile perovskite lasers. In particular, two questions remain open: why the Amplified Spontaneous Emission (ASE) band is significantly shifted from the fluorescence one, and why the former seems to suddenly emerge from, and coexist with, the latter. These characteristic features have led to a debate, which is not settled yet, on which is the mechanism behind the ASE band shift. In this communication, we try to settle this debate and address these questions through experimental ASE measurements combined with numerical simulations. We show that the ASE behaviour in CsPbBr3 NCs thin films stems from a combination of reabsorption, excited state absorption, excitation of differently polarized waveguide modes, and the coexistence of short- and long-lived localized single excitons. The results in this work help understanding the stimulated emission mechanisms in perovskites and provide insightful information on research avenues to increase the efficiency of the light-emitting devices based on these materials.

Modulation of Auger recombination via facet engineering in CsPbBr3 perovskite nanocrystals

We demonstrate the modulation of Auger recombination via facet engineering in CsPbBr3 perovskite nanocrystals, where the static dielectric screening effect is revealed to prevail over the dynamic polaronic screening effect.

CsZnPbBr3/ZnS core/shell perovskite nanocrystals for stable and efficient white light-emitting diodes.

The widespread applicability of perovskite nanocrystals (PeNCs) is impeded by their intrinsic instability. A promising solution is utilizing robust chalcogenides as a protective shell to shield the sensitive luminescent cores from the external environment. However, the inferior structural stability and surface lability of PeNCs usually lead to perovskite phase transition during shell growth. Herein, we introduced smaller Zn ions to partially replace Pb ions in perovskites, which reduces the Pb-X bond length and enhances the Pb-X bond energy for inner lattice stabilization. Simultaneously, extra oleylammonium bromide (OAmBr) was added to protect the labile surface of PeNCs by compensating for the detachment of ligands and the loss of surface Br ions. As a result, the dual strategies enable the epitaxial growth of a ZnS shell and significantly enhance the chemical stability of CsZnPbBr3/ZnS core/shell PeNCs. After three thermal cycles ranging from 300 to 450 K, the core/shell PeNCs retained 70% of their initial photoluminescence (PL) intensity. In stark contrast, the pristine CsPbBr3 PeNCs exhibit complete PL quenching after just the first temperature cycle. For practical applications, the green core/shell PeNCs were integrated with commercially available red-emitting phosphors on a blue-emitting InGaN chip to fabricate a white light-emitting diode (WLED), which demonstrates a high luminous efficacy (LE) of 61.3 lm W-1 and nearly constant Commission Internationale de l'Eclairage (CIE) coordinates under varying operating currents.

Long live(d) CsPbBr3 superlattices: colloidal atomic layer deposition for structural stability.

Superlattice formation afforded by metal halide perovskite nanocrystals has been a phenomenon of interest due to the high structural order induced in these self-assemblies, an order that is influenced by the surface chemistry and particle morphology of the starting building block material. In this work, we report on the formation of superlattices from aluminum oxide shelled CsPbBr3 perovskite nanocrystals where the oxide shell is grown by colloidal atomic layer deposition. We demonstrate that the structural stability of these superlattices is preserved over 25 days in an inert atmosphere and that colloidal atomic layer deposition on colloidal perovskite nanocrystals yields structural protection and an enhancement in photoluminescence quantum yields and radiative lifetimes as opposed to gas phase atomic layer deposition on pre-assembled superlattices or excess capping group addition. Structural analyses found that shelling resulted in smaller nanocrystals that form uniform supercrystals. These effects are in addition to the increasingly static capping group chemistry initiated where oleic acid is installed as a capping ligand directly on aluminum oxide. Together, these factors lead to fundamental observations that may influence future superlattice assembly design.

The more the merrier: optimizing monomer concentration for supersaturation controlled synthesis of stable ultra-small CsPbBr3 nanocrystals for blue emission.

Synthesis of strongly quantum confined and emissive CsPbBr3 perovskite nanocrystals with sizes <4 nm has proven challenging owing to fast nucleation and rapid growth. In this work, ultra-small blue-emitting (∼461 nm) CsPbBr3 nanocrystals with an average particle size of 3.2 nm are synthesized via a high-temperature (170 °C) colloidal approach by controlling the supersaturation reaction conditions. Our approach yielded stable nanocrystals with uniform size, shape, and excellent color purity, making them promising for blue light emitting diode (LED) applications.

Chiral defect-induced blue photoluminescence and circularly polarized luminescence of zero-dimensional Cs4PbBr6 perovskite nanocrystals

Chiral-defect-induced strategy is employed to synthesize zero-dimensional chiral Cs4PbBr6 perovskite nanocrystals (NCs) with blue photoluminescence and CPL response via a phase transition process.

Mechanistic Insights into the Photoluminescence Enhancement in Surface Ligand Modified CsPbBr3 Perovskite Nanocrystals.

We report a mechanistic study of the photoluminescence (PL) enhancement in CsPbBr3 perovskite nanocrystals (PNCs) induced by organic/inorganic hybrid ligand engineering. Compared to the as-synthesized oleic acid-oleylamine modified PNCs, the tributylphosphine oxide-CaBr2 modified PNCs can achieve a better passivation effect due to strong P═O-Pb coordination and Br-vacancy remedy, resulting in enhanced PL efficiency. We employ steady-state/time-resolved/temperature-dependent PL and fluence/polarization-dependent ultrafast transient absorption spectroscopy to obtain a mechanistic understanding of such an enhancement effect from both nonradiative and radiative perspectives. As for the dominating nonradiative recombination suppression, we quantitatively evaluate the contributions from channels of exciton dissociation and exciton trapping, which are connected to exciton binding energy and activation energy of exciton trapping to surface defect-induced trap states, respectively. We also look into the radiative recombination enhancement, which is likely due to the increase in electron-hole overlap of photogenerated excitons induced by slight Ca-doping. These mechanistic insights would be of guiding value for perovskite-based light-emitting applications.

Insight into the growth kinetics of CsPbBr3 perovskite nanocrystals using an oil-water droplet fluidic synthesis route

All-inorganic lead halide perovskite nanocrystals (PNCs) have attracted extensive attention in the optoelectronic fields owning to their exceptional photoluminescence characteristics. However, the ultra-fast growth rate of PNCs leads to challenges in controlling their size and optical properties. Here, we report a water–oil droplet fluidic synthesis method that successfully slow down the growth rate of CsPbBr3 PNCs by segregating the cation and anion precursors in the respective phases. Reaction mechanism study revealed a fast nucleation via a nanoplate-intermediate pathway upon HBr diffusion and subsequent slow growth through ripening, leading to a wide range of spectral tunability of the PNCs from 445 nm to 520 nm. The theoretical investigation into growth kinetics showed the combined effect of the ligands and temperature on the growth of the PNCs. This method provides an efficient means for producing high-performance PNCs with tunable size and wavelength while also eliminating the requirement for a Pb-rich reaction environment.

Ultrastable Dual-Matrix meditated CsPbBr3 composites with enhanced photoluminescence quantum yield and robust circular polarization luminescence

Metal halide perovskite materials have emerged as a focal point of research in the field of circularly polarized luminescence (CPL). However, striking a delicate balance between several crucial parameters, including large luminescence dissymmetry factors (glum), high photoluminescence quantum yields (PLQY), and long-term stability, has proven to be a challenging endeavor. Here, this study presented a pioneering strategy for crafting robust CPL-active inorganic nanomaterial composites utilizing dual-matrix of chiral nematic mesoporous silica (CNMS) and inorganic passivation Cs4PbBr6 layer. The use of free-standing CNMS hard templates provided a confined growth environment for all-inorganic CsPbBr3 perovskite nanocrystals, enabling the conversion of unpolarized light emission into CPL. Through further advancements in the form of effective passivation with inorganic Cs4PbBr6 layer, superior optical performance and stability were achieved in the system. The figure of merit (FM) value for the resultant CsPbBr3/Cs4PbBr6@CNMS composite film reached −7.8 × 10−2, surpassing the performance of current advanced systems. Moreover, the surface passivation, along with the protection offered by the dual-matrix encapsulation, enhanced the resilience of composite film to harsh environments with robust performance. The successful integration of the CPL materials into a circularly polarized light-emitting diode device confirmed their applicability in CPL displays and luminescence applications. This work establishes a reliable and efficient method for the development of high-performance CPL materials and applications.

Monodentate binding of zwitterionic ligands for boosting photocatalytic H2 production of perovskite nanocrystals

Perovskite nanocrystals (PNCs) have recently emerged as promising materials for photocatalytic applications. However, weakly bound and long-chain surface ligands on PNCs reduce the colloidal stability, hinder efficient charge transfer, and lower the photocatalytic activity. Herein, we report zwitterionic sulfobetaine (ZSB) ligand-capped CsPbBr3perovskite nanocrystals (PNCs) for visible-light-driven photocatalytic H2 production. In this system, the ZSB ligands passivate PNC surface defects, thus improving the photoluminescence stability and quantum yield. In particular, the positively charged R4N+groups of the ZSB ligands preferentially bind to the Br-rich CsPbBr3PNC surface, leaving unpaired negative SO3− groups in the outermost ligand layer. This unbalanced binding of the ZSB ligands changes the surface potential of the PNCs from positive to negative, inducing a kinetically favorable band alignment at the heterojunction between the PNC and co-catalyst (Pt-deposited TiO2). The heterojunction and electronic structures are stable, even in harsh aqueous environments, resulting in significantly enhanced electron transfer and H2 production rates and greatly improved operational stability. We believe that the use of ZSB ligands for band engineering is highly promising for PNC-based photocatalysis and solar energy conversion systems.

Evolution of the Luminescence Properties of Single CsPbBr&lt;sub&gt;3&lt;/sub&gt; Perovskite Nanocrystals During Photodegradation

The evolution of the luminescence blinking of single CsPbBr3perovskite nanocrystals with a characteristic size of ~25 nm during photodegradation has been experimentally investigated. It has been demonstrated that the blue shift of the luminescence peak and a decrease in the average luminescence intensity are accompanied by the increasing role of nonradiative Auger processes underlying the charging mechanism of blinking. A method based on the analysis of photon antibunchingg2(0) and exciton and biexciton recombination rates is used to determine the blinking mechanism. The data obtained have made it possible to reveal a transition from the trapping to charging blinking mechanism with a change in the sizes of a CsPbBr3single nanocrystal.

A Strategy for Tuning Electron-Phonon Coupling and Carrier Cooling in Lead Halide Perovskite Nanocrystals.

Perovskites have been recognized as a class of promising materials for optoelectronic devices. We intentionally include excessive Cs+ cations in precursors in the synthesis of perovskite CsPbBr3 nanocrystals and investigate how the Cs+ cations influence the lattice strain in these perovskite nanocrystals. Upon light illumination, the lattice strain due to the addition of alkali metal Cs+ cations can be compensated by light-induced lattice expansion. When the Cs+ cation in precursors is about 10% excessive, the electron-phonon coupling strength can be reduced by about 70%, and the carrier cooling can be slowed down about 3.5 times in lead halide perovskite CsPbBr3 nanocrystals. This work reveals a new understanding of the role of Cs+ cations, which take the A-site in ABX3 perovskite and provide a new way to improve the performance of perovskites and their practical devices further.

Enhancing Multiexcitonic Emission in Metal-Halide Perovskites by Quantum Confinement.

Semiconductor metal halide perovskite nanocrystals have been under intense investigation for their promise in a variety of optoelectronic applications, which arises from their remarkable properties of defect tolerance and efficient light emission. Recently, quantum dot versions of perovskite nanocrystals have been available, enabling investigation of how quantum size effects control optical function and performance in these quantum dots (QD), past their well-known covalent II-VI analogues. We perform time-resolved photoluminescence (t-PL) experiments on CsPbBr3 perovskite nanocrystals spanning in diameter from 5.8 nm strongly confined quantum dots to 18 nm weakly confined quantum dots. Experiments are performed with sufficient time resolution of 3 ps to observe the interaction energies and recombination kinetics from excitons to multiexcitons. Comparing the same sized QD reveals that perovskite QD have a larger radiative rate constant for emission from X than CdSe QD due to a larger oscillator strength. The multiexciton (MX) regime reveals that perovskite QD emit brightly and with more focused bandwidth than equivalent sized CdSe QD enabling more spectrally pure brightness. The MX kinetics reveals that the perovskite QD maintain efficient radiative decay, effectively competing with Auger recombination. These experiments reveal that the strongly confined QD of perovskites can be efficient multiexcitonic emitters, such as in high brightness light emitting diodes, especially in the blue.

Boosting the Performance of Photomultiplication-Type Organic Photodiodes by Embedding CsPbBr3 Perovskite Nanocrystals.

In this study, it is demonstrated that CsPbBr3 perovskite nanocrystals (NCs) can enhance the overall performances of photomultiplication-type organic photodiodes (PM-OPDs). The proposed approach enables the ionic-polarizable CsPbBr3 NCs to be evenly distributed throughout the depletion region of Schottky junction interface, allowing the entire trapped electrons within the depletion region to be stabilized, in contrast to previously reported interface-limited strategies. The optimized CsPbBr3 -NC-embedded poly(3-hexylthiophene-diyl)-based PM-OPDs exhibit exceptionally high external quantum efficiency, specific detectivity, and gain-bandwidth product of 2,840,000%, 3.97×1015 Jones, and 2.14×107 Hz, respectively. 2D grazing-incidence X-ray diffraction analyses and drift-diffusion simulations combined with temperature-dependent J-V characteristic analyses are conducted to investigate the physics behind the success of CsPbBr3 -NC-embedded PM-OPDs. The results show that the electrostatic interactions generated by the ionic polarization of NCs effectively stabilize the trapped electrons throughout the entire volume of the photoactive layer, thereby successfully increasing the effective energy depth of the trap states and allowing efficient PM mechanisms. This study demonstrates how a hybrid-photoactive-layer approach can further enhance PM-OPD when the functionality of inorganic inclusions meets the requirements of the target device.

Persistent Charging of CsPbBr3 Perovskite Nanocrystals Confined in Glass Matrix.

Manipulation of persistent charges in semiconductor nanostructure is the key point to obtain quantum bits towards the application of quantum memory and information devices. However, realizing persistent charge storage in semiconductor nano-systems is still very challenge due to the disturbance from crystal defects and environment conditions. Herein, the two-photon persistent charging induced long-lasting afterglow and charged exciton formation are observed in CsPbBr3 perovskite nanocrystals (NCs) confined in glass host with effective lifetime surpassing one second, where the glass inclosure provides effective protection. A method combining the femtosecond and second time-resolved transient absorption spectroscopy is explored to determine the persistent charging possibility of perovskite NCs unambiguously. Meanwhile, with temperature-dependent spectroscopy, the underlying mechanism of this persistent charging is elucidated. A two-channel carrier transfer model is proposed involving athermal quantum tunneling and slower thermal-assisted channel. On this basis, two different information storage devices are demonstrated with the memory time exceeding two hours under low-temperature condition. These results provide a new strategy to realize persistent charging in perovskite NCs and deepen the understanding of the underlying carrier kinetics, which may pave an alternative way towards novel information memory and optical data storage applications.

Photocatalytic CO2 Reduction Coupled with Oxidation of Benzyl Alcohol over CsPbBr3@PANI Nanocomposites.

Herein, we successfully prepare conductive polyaniline (PANI)-encapsulated CsPbBr3 perovskite nanocrystals (PNCs) that demonstrate much improved photocatalytic performance and stability toward the CO2 reduction reaction (CRR) coupled with oxidation of benzyl alcohol (BA) to benzaldehyde. Due to the acid-base interaction between CO2 and PANI, CO2 molecules are selectively adsorbed on PANI in the form of carbamate. As a result, the rate of production of CO (rCO) reaches 26.1 μmol g-1 h-1 with a selectivity of 98.1%, which is in good agreement with the rate of oxidation (∼27.0 μmol g-1 h-1) of BA. Such a high reduction/oxidation rate is enabled by the fast electron transfer (∼2.2 ps) from PNCs to PANI, as revealed by femtosecond transient absorption spectroscopy. Moreover, because of the benefit of the encapsulation of PANI, no significant decrease in rCO is observed in a 10 h CRR test. This work offers insight into how to simultaneously achieve improved photocatalytic performance and stability of CsPbX3 PNCs.

Optical Properties of Composites based on CsPbBr3 Perovskite Nanocrystals and Polymer Matrices as Promising Components of Next-generation Scintillation Detectors

Optical Properties of Composites based on CsPbBr3 Perovskite Nanocrystals and Polymer Matrices as Promising Components of Next-generation Scintillation Detectors

Controlled Modification of the Optical Properties of CsPbBr3 Perovskite Nanocrystals by Chemical Treatment of Their Surface

Controlled Modification of the Optical Properties of CsPbBr3 Perovskite Nanocrystals by Chemical Treatment of Their Surface

Synthesis of a water-stable CsPbBr3 perovskite for selective detection of mercury ion in water.

By using the method of low-temperature crystallization, CsPbBr3 perovskite nanocrystals (PNCs) coated with trifluoroacetyl lysine (Tfa-Lys) and oleamine (Olam) were synthesized in aqueous solution. The structure of the CsPbBr3 PNCs was characterized by many methods, such as ultraviolet (UV)-visible absorption spectrophotometer, fluorescence spectrophotometer, transmission electron microscopy (TEM), and X-ray diffraction (XRD) pattern. The fluorescence emission of the CsPbBr3 PNCs is stable in water for about 1 day at room temperature. It was also found that the fluorescence of the PNCs could be obviously and selectively quenched after the addition of mercury ion (Hg2+ ), allowing a visual detection of Hg2+ by the naked eye under UV light illumination. The fluorescence quenching rate (I0 /I) has a good linear relationship with the addition of Hg2+ in the concentration range 0.075 to 1.5 mg/L, with a correlation coefficient (R2 ) of 0.997, and limit of detection of 0.046 mg/L. The fluorescence quenching mechanism of the PNCs was determined by the fluorescence lifetime and X-ray photoelectron spectroscopy (XPS) of the PNCs. Overall, the synthesis method for CsPbBr3 PNCs is simple and rapid, and the as-prepared PNCs are stable in water that could be conveniently used for selective detection of Hg2+ in the water environment.

Tertiary amine oxides as perovskite nanocrystal ligands and components of polymeric nanocomposites

AbstractAs a class of semiconductor nanocrystals that exhibit high photoluminescence quantum yield (PLQY) at tunable wavelengths, perovskite nanocrystals (PNCs) are attractive candidates for optoelectronic and light‐emitting devices. However, attempts to optimize PNC integration into such applications suffer from PNC instability and loss of PL over time. Here, we describe the impact of organic and polymeric N‐oxides when used in conjunction with PNCs, whereby a significant increase in PNC quantum yield is observed in solution, and stable PL emission is obtained in polymeric nanocomposites. Specifically, when using aliphatic N‐oxides in ligand exchange with CsPbBr3 PNCs in solution, a substantial boost in PNC brightness is observed (~40% or more PLQY increase), followed by an alteration of the perovskite chemistry. When N‐oxide substituents are positioned pendent to a poly(n‐butyl methacrylate) backbone, the optically clear flexible nanocomposite films obtained have bright PL emission and maintain optical clarity for months. X‐ray diffraction is useful for characterizing the PNC crystalline structure following exposure to aliphatic N‐oxides, while electron microscopy (EM) and small‐angle X‐ray scattering (SAXS) measurements of the PNC‐polymer nanocomposites show this polymeric N‐oxide platform to cleanly disperse PNCs in flexible polymer films.