CsPbBr3 Nanocrystal Film Research Articles

In Situ Growth Method for Large-Area Flexible Perovskite Nanocrystal Films.

Metal halide perovskites have shown unique advantages compared with traditional optoelectronic materials. Currently, perovskite films are commonly produced by either multi-step spin coating or vapor deposition techniques. However, both methods face challenges regarding large-scale production. Herein, we propose a straightforward in situ growth method for the fabrication of CsPbBr3 nanocrystal films. The films cover an area over 5.5 cm × 5.5 cm, with precise thickness control of a few microns and decent uniformity. Moreover, we demonstrate that the incorporation of magnesium ions into the perovskite enhances crystallization and effectively passivates surface defects, thereby further enhancing luminous efficiency. By integrating this approach with a silicon photodiode detector, we observe an increase in responsivity from 1.68 × 10-2 A/W to 3.72 × 10-2 A/W at a 365 nm ultraviolet wavelength.

Enhancement of nonlinear optical effects of pure and Mn-doped CsPbBr3 perovskite films by external voltage

CsPbBr3 and Mn:CsPbBr3 nanocrystal (NC) films were prepared on indium tin oxide (ITO) glass by a slow solvent evaporation method. The ITO layer was applied a voltage to enhance the nonlinear optical (NLO) properties of CsPbBr3 and Mn:CsPbBr3 nanocrystal (NC) films. When the voltage is zero, the Z-scan results show that the nonlinear absorption (NLA) coefficients β of CsPbBr3 and Mn:CsPbBr3 NC films are 1.60 × 103 cm/GW and 1.54 × 104 cm/GW, respectively. The nonlinear refraction (NLR) coefficients γ of CsPbBr3 and Mn:CsPbBr3 NC films are 2.07 × 10−5 cm2/W and 2.48 × 10−5 cm2/W, respectively. Subsequently, the voltages of 5.03–13.42 V were applied to the ITO layer. Finally, when the voltage is 13.42 V, the β values of CsPbBr3 (1.75 × 104 cm/GW) and Mn:CsPbBr3 (3.98 × 104 cm/GW) NC films are 10.9 and 2.6 times higher than those without the applied voltage, respectively. The γ values of CsPbBr3 and Mn:CsPbBr3 NC films are 3.73 × 10−5 cm2/W and 3.88 × 10−5 cm2/W, respectively. This research proposes an effective method to improve the third-order NLO performances of CsPbBr3 and Mn:CsPbBr3 NC films by applying voltage.

Aging Effects on the Exciton Relaxation and Diffusion Processes in CsPbBr3 Nanocrystals

AbstractFully inorganic perovskite nanocrystals (NCs) have been widely investigated due to their potential as very interesting active materials for several types of photonic and optoelectronic devices. Despite several experiments designed to investigate the basic emission properties of these NCs, a clear and complete understanding of their photophysics is still missing. In this work, temperature‐dependent steady state and time‐resolved photoluminescence (PL) measurements are used to investigate the nature of the emitting states, the origin of the excitation relaxation dynamics and the effects of aging upon long exposure to wet air for thin films of CsPbBr3 NCs prepared by coprecipitation. It is demonstrated that both free excitons and localized excitons contribute to the NC emission and that electron traps within the conduction band, ≈14 meV and ≈80 meV above the band edge, determine thermal emission quenching. Moreover, it is shown that the non‐exponential PL relaxation dynamics are due to short‐range energy migration within a disordered distribution of localized states between 10 and 100 K, with activation of a second, long‐range diffusion process at higher temperatures. It is also demonstrated that aging determines the variations in defect levels, exciton‐phonon coupling and exciton relaxation dynamics. The results substantially improve the current understanding of the basic photophysics of CsPbBr3 NC films and of the aging effects and are expected to provide a useful guide for future characterization of other similar materials.

Solution-Processed Synaptic Memristors Based on Halide Perovskite Nanocrystals.

Exploring new materials and structures to construct synaptic devices represents a promising route to fundamentally approach novel forms of computing. Nanocrystals (NCs) of halide perovskites possess unique charge transport characteristics, i.e., ionic-electronic coupling, holding considerable promise for energy-efficient and reconfigurable artificial synapses. Herein, we report solution-processed thin-film memristors from all-inorganic CsPbBr3 perovskite NCs, functioning as an electrically programmable analog memory with good stability. The devices are demonstrated to successfully emulate a number of essential synaptic functions with low power consumption, including reversible potentiation and depression, short-term plasticity (STP), paired-pulse facilitation (PPF), and long-term plasticity (LTP), such as spike-number-dependent plasticity (SNDP), spike-rate-dependent plasticity (SRDP), spike-timing-dependent plasticity (STDP), and spike-voltage-dependent plasticity (SVDP). It is proposed that a coupled capacitive and inductive phenomenon originating from charge trapping and ion migration in CsPbBr3 NC films, controlled by the amplitude and timing of the programming pulses, defines the degree of synaptic plasticity. A transition emerges from the fast trap-related capacitive regime to a slow ionic inductive regime, which enables continuous change of the film resistance and the magnitude of the electronic current, analogous to the synaptic weight modulation in biological synapses.

Achieving direct electrophoretically deposited highly stable polymer induced CsPbBr3 colloidal nanocrystal films for high-performance optoelectronics

Synthesizing colloidal nanocrystals (NCs) with long-term stable under ambient conditions via appropriate ligands capping is highly challenging. Herein, the rapid synthesis of CsPbBr3 colloidal NCs at room temperature using polyvinylpyrrolidone as the primary ligand is demonstrated. The addition of ethylene glycol stabilizes the colloidal NCs and enhance their photoluminescence by ∼ 5-fold. Colloidal NCs have a net negative surface charge, which enables the direct electrophoretic deposition of a polymer-induced all-inorganic CsPbBr3 NC film with ultra-high stability under ambient conditions at relative humidity of 55% for 240 days. As an example of the application of the CsPbBr3 NC film in an optoelectronic device, a hybrid MoS2/CsPbBr3 field-effect phototransistor is fabricated, which exhibits a detectivity of 9 × 1012 Jones and an ultra-high responsivity of 1.2 × 107 A W−1 under the illumination of 450-nm laser at 4.4 pW. The noble and practical methods applied in our CsPbBr3 NC films could be extended to produce various types of uniform NC films over a large geometrical area with outstanding long-term environmental stability, holding significant promise for use in a broad range of advanced optoelectronic devices.

Electrical and Optical Characteristics of CsPbI-=SUB=-3-=/SUB=- and CsPbBr-=SUB=-3-=/SUB=- Lead Halide Perovskite Nanocrystal Films Deposited on c-Si Solar Cells for Photovoltaic Applications

The deposition of an additional layer of nanoparticles is a widely used method for improving the optical and electrical characteristics of semiconductor solar cells (SCs). In this work, films of nanocrystals (NC) of inorganic perovskites of lead halides CsPbI3 and CsPbBr3 are deposited on the surface of a solar cell based on crystalline silicon (c-Si). It is shown that the optical properties of such NC films are in good agreement with the optical properties of c-Si. It has been found that the absorption coefficient of solar cells with NC layers of inorganic perovskites is much higher in the visible region of the spectrum, which increases the photocurrent generation in the SC in the range of 370-900 nm. A significant effect of surface roughness on the photoelectric properties of solar cells has been found. CsPbI3 NC films have a textured surface and higher photocurrent than CsPbBr3 NC films, which are rougher. Enhanced photovoltaic properties of photoelectric structures with a CsPbI3 NC layer compared to CsPbBr3 NC films due to their lower degree of roughness were observed. Keywords: perovskite nanocrystals, silicon solar cells, reflection spectra, photoluminescence, electrical conductivity.

Электрические и оптические характеристики пленок нанокристаллов перовскитов галогенида свинца CsPbI-=SUB=-3-=/SUB=- и CsPbBr-=SUB=-3-=/SUB=-, нанесенных на c-Si солнечные элементы для фотовольтаических приложений

The deposition of an additional layer of nanoparticles is a widely used method for improving the optical and electrical characteristics of semiconductor solar cells (SCs). In this work, films of nanocrystals (NC) of inorganic perovskites of lead halides CsPbI3 and CsPbBr3 are deposited on the surface of a solar cell based on crystalline silicon (c-Si). It is shown that the optical properties of such NC films are in good agreement with the optical properties of c-Si. It has been found that the absorption coefficient of solar cells with NC layers of inorganic perovskites is much higher in the visible region of the spectrum, which increases the photocurrent generation in the SC in the range of 370–900 nm. A significant effect of surface roughness on the photoelectric properties of solar cells has been found. CsPbI3 NC films have a textured surface and higher photocurrent than CsPbBr3 NC films, which are rougher. Enhanced photovoltaic properties of FE structures with a CsPbI3 NC layer compared to CsPbBr3 NC films due to their lower degree of roughness were observed.

Switchable All Inorganic Halide Perovskite Nanocrystalline Photoelectrodes for Solar‐Driven Organic Transformations

All inorganic halide perovskite nanocrystals (NCs) are considered as fascinating materials for a wide range of optoelectronic applications encompassing photovoltaics, lasing, sensing, and photocatalysis due to their outstanding optoelectronic properties. Herein, it is demonstrated that the photoelectrochemical behavior of CsPbBr3 NC films can be tailored through engineering the selective contacts and accepting species in the electrolyte. This concept has been successfully applied to the photoelectrochemical oxidation of benzyl alcohol (BzOH) to benzyl aldehyde (BzCHO) and the reverse photoelectrochemical reduction of BzCHO to BzOH, demonstrating that CsPbBr3 NCs activate both reactions with photocurrents up to 40 μA cm−2 toward BzCHO production and 5 μA cm−2 for the reverse reaction at 0.15 V versus normal hydrogen electrode. The obtained results highlight the huge potential and versatility of halide perovskite NCs for photoelectrocatalytic applications, validating the implementation of these materials for a wide range of solar‐driven complex organic transformations, and emphasizing the urgent need for stabilization strategies to move beyond the proof‐of‐concept stage to relevant technological developments.

Effect of alkali metal nitrate treatment on the optical properties of CsPbBr3 nanocrystal films

Colloidal cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs) are fabricated as densely packed thin films using doctor blade method through a layer-by-layer assembly approach. It is found that the optical properties of the CsPbBr3 NC films are significantly improved after a ligand exchange of oleic acid (OA) and oleylamine (OAm) by sodium and potassium nitrate in ethyl acetate. Ligand-induced surface defects are passivated by the sodium and potassium cations and nitrate, which leads to the improvement in photoluminescence (PL) and life-time properties. Compared with pristine OAm-OA capped CsPbBr3 NC film, Alkali-metal nitrate salts treated films are showing higher PL intensity and longer carrier-lifetime, evidencing their potential use to achieve defect-free inorganic perovskite NC films.

Water-driven CsPbBr3 nanocrystals and poly(methyl methacrylate)-CsPbBr3 nanocrystal films with bending-endurable photoluminescence

Perovskite nanocrystals are regarded as next-generation functional materials for display applications, especially for flexible liquid crystal displays (LCDs). As a potential component of flexible LCD backlights, perovskite nanocrystal films are facing a challenge issue of deformation-induced shift of photoluminescence, leading to an image distortion. To date, most synthesis methods have involved the use of organic solvent in precursor solutions, such as N,N-dimethylformamide and dimethyl sulfoxide, which poses a potential threat to the environment, health and security. In this work, we demonstrate the feasibility to produce microsized CsPbBr3 crystals with deionized water as the precursor solvent via an environmental-friendly and cost-efficient approach and CsPbBr3 nanocrystals with green (~522 nm) and blue (~493 nm) emissions from the microsized CsPbBr3 crystals in toluene under sonication. The blue-emitting nanocrystals exhibit a photoluminescence (PL) quantum yield of 80%, much larger than 61.4% of the CsPbBr3 nanocrystals made by an anti-solvent method; the green-emitting nanocrystals exhibit better stability than those made by the antisolvent method over 9 days. Using the green-emitting CsPbBr3 nanocrystals, we prepare a bilayer structure with a poly(methyl methacrylate)-CsPbBr3 nanocrystal film on a polyethylene terephthalate plate. The films exhibit bending-endurable photoluminescence, i.e. the wavelength of the PL peak remains unchanged, for local radius of curvature of the bilayer up to 10.07 mm under bending. This study opens a new avenue to potentially produce microsized perovskite crystals without harmful organic solvents and bending-endurable backlight films for the applications in flexible display.

Local Morphology Effects on the Photoluminescence Properties of Thin CsPbBr3 Nanocrystal Films.

Lead halide perovskites are emerging as extremely interesting active materials for a wide variety of optoelectronic and photonic devices. A deep understanding of their photophysics is thus fundamental in order to properly understand the origins of the materials active properties and to provide strategies for improving them. In this work, we exploit the local morphological variations in a drop-cast thin CsPbBr nanocrystal film to show that the aggregation of NCs has strong effects on the peak wavelengths of PL spectra, the linewidth, and the intensity of dependence on temperature. An analysis based on models that are frequently used in the literature led to completely different conclusions about the intrinsic NC emission properties extracted from spectra measured in points with different contribution of the PL from the aggregates. Our results demonstrate that extreme care has to be used in order to correctly correlate the spectral PL features with the intrinsic emission properties of lead halide perovskite NC films.

Completely Amine-Free Open-Atmospheric Synthesis of High-Quality Cesium Lead Bromide (CsPbBr3 ) Perovskite Nanocrystals.

Cesium lead halide perovskite nanocrystals (NCs) CsPbX3 (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light-emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX3 synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine-free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri-n-octylphosphane as ligand under open-atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three-precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single-source precursor for Pb and Br (PbBr2 ). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr3 NCs with high PLQY were found. These completely amine-free CsPbBr3 perovskite NCs synthesized under bromine-rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open-atmosphere-stable CsPbBr3 NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.

Strong photocharging effect in CsPbBr3 nanocrystal films

In this study, a strong photocharging effect has been detected by a spectroscopic study of colloidal CsPbBr3 quantum dot film. Photocharging induces the formation of charged excitons, even with the application of a very low excitation laser power. Thus, it can introduce a drastic problem on the optical properties of quantum dots when the charges are involved. The charge exciton then can absorb another photon from the next laser pulse, leading to a trion state. The presence of the trion state was proven by studying its behavior against three effects, namely laser power, electric field (EF) and temperature (T) dependence. The trion area of the peak increases linearly with the increasing of the laser power, which we consider to be an indication of the influence of a strong photocharging effect, suggesting that long-lived charges can be kept trapped in quantum dots (QDs). It was also found the trion is affected by an external electric field, due to the weak Stark effect. It is more sensitive than the excitonic state to the electric field due to the presence of electron–electron repulsion forces. A red-shift behavior was observed when heating the sample above 180 K, which is a strong evidence of the presence of a trapping state.

Enhancement of the optical properties of CsPbBr3 perovskite nanocrystals using three different solvents.

Green-emitting CsPbBr3 perovskite nanocrystals were synthesized by the modified hot-injection method using three different solvents. The produced nanocrystals showed a narrow green emission band centered at 515-520 nm with full width at half-maximum (FWHM) values of approximately 18-20 nm. The highest photoluminescence quantum yield (PLQY) was obtained for the nanocrystal sample synthesized using a paraffin liquid solvent, with a value of 70.1% under excitation at 450 nm. The CsPbBr3 nanocrystals film light-emitting diodes (LED) chip module showed a luminous efficacy of 40.7lm/Wrad. The white LED (WLED) with green CsPbBr3 and red CsPbI3 nanocrystal films emitted bluish-white light with a high color rendering index of 89, and the luminous efficacy of the WLED reached 16.3lm/Wrad.

CsPbBr3 Nanocrystal Films: Deviations from Bulk Vibrational and Optoelectronic Properties

AbstractMetal‐halide perovskites (MHP) are highly promising semiconductors for light‐emitting and photovoltaic applications. The colloidal synthesis of nanocrystals (NCs) is an effective approach for obtaining nearly defect‐free MHP that can be processed into inks for low‐cost, high‐performance device fabrication. However, disentangling the effects of surface ligands, morphology, and boundaries on charge‐carrier transport in thin films fabricated with these high‐quality NCs is inherently difficult. To overcome this fundamental challenge, terahertz (THz) spectroscopy is employed to optically probe the photoconductivity of CsPbBr3 NC films. The vibrational and optoelectronic properties of the NCs are compared with those of the corresponding bulk polycrystalline perovskite and significant deviations are found. Charge‐carrier mobilities and recombination rates are demonstrated to vary significantly with the NC size. Such dependences derive from the localized nature of charge carriers within NCs, with local mobilities dominating over interparticle transport. It is further shown that the colloidally synthesized NCs have distinct vibrational properties with respect to the bulk perovskite, exhibiting blue‐shifted optical phonon modes with enhanced THz absorption strength that also manifest as strong modulations in the THz photoconductivity spectra. Such fundamental insights into NC versus bulk properties will guide the optimization of nanocrystalline perovskite thin films for optoelectronic applications.

Photo- and electroluminescence features of films and field effect transistors based on inorganic perovskite nanocrystals embedded in a polymer matrix

The optical and electrical properties of films and field-effect transistors (FETs) based on pure MEH-PPV, neat CsPbBr3 nanocrystals (NCs), and MEH-PPV:CsPbBr3 NCs composites with different contents of CsPbBr3 NCs are investigated. The films were characterized by absorbance, atomic-force microscope and current-voltage characteristics (I-Vs) techniques. Relative PL and EL intensities and PL spectra of the pure MEH-PPV, neat CsPbBr3 NCs and MEH-PPV:CsPbBr3 NCs films were measured at 300 K at various levels of optical and electrical excitation power; these dependencies of the PL and EL intensities turned out to be sublinear and superlinear respectively. FETs based on MEH-PPV:CsPbBr3 NCs (1:1) films exhibit I-Vs at 290 – 100 K a dominant hole transport mechanism. The mobility of charge carriers was determined at 290 K for neat CsPbBr3 NCs (for electrons: 2.7 10−2 cm2/Vs) and MEH-PPV:CsPbBr3 NCs (1:1) (for holes: 9 cm2/Vs). The temperature dependence of the hole mobility μFET(T) of FETs based on MEH-PPV:CsPbBr3 NCs (1:1) films characteristic of the hopping mode. It was found that the superlinearity of the dependence of EL of MEH-PPV:CsPbBr3 NCs LE-FETs at 290 K increases with increasing concentration of CsPbBr3 NCs due to efficient energy transfer between CsPbBr3 NCs and the MEH-PPV polymer matrix, and also because of the probability of electron tunneling through the potential barrier to electrode. It is expected that the obtained MEH-PPV:CsPbBr3 NCs nanocomposite films will be useful for efficient applications in nanotechnology LEDs, FETs and LE-FETs.

Amplified Spontaneous Emission Threshold Reduction and Operational Stability Improvement in CsPbBr3 Nanocrystals Films by Hydrophobic Functionalization of the Substrate

The use of lead halide perovskites in optoelectronic and photonic devices is mainly limited by insufficient long-term stability of these materials. This issue is receiving growing attention, mainly owing to the operational stability improvement of lead halide perosvkites solar cells. On the contrary, fewer efforts are devoted to the stability improvement of light amplification and lasing. In this report we demonstrate that a simple hydrophobic functionalization of the substrates with hexamethyldisilazane (HMDS) allows to strongly improve the Amplified Spontaneous Emission (ASE) properties of drop cast CsPbBr3 nanocrystal (NC) thin films. In particular we observe an ASE threshold decrease down to 45% of the value without treatment, an optical gain increase of up to 1.5 times and an ASE operational stability increase of up to 14 times. These results are ascribed to a closer NC packing in the films on HMDS treated substrate, allowing an improved energy transfer towards the larger NCs within the NC ensemble, and to the reduction of the film interaction with moisture. Our results propose hydrophobic functionalization of the substrates as an easy approach to lower the ASE and lasing thresholds, while simultaneously increasing the active material stability.

Ultraviolet light induced degradation of luminescence in CsPbBr3 perovskite nanocrystals

Perovskite nanocrystals (NCs) have been applied in light emitting diodes, but their stability is always the decisive factor to limit the practical application of devices. In this work, the influence of ultraviolet light illumination on the structural and luminescent properties of CsPbBr3 NC films with emissions of 495 and 520 nm was studied. It was demonstrated that the CsPbBr3 NC films exhibited significant degradation of photoluminescence (PL) under the illumination in air. The PbCO3 and PbO phases in CsPbBr3 NC films were observed after long illumination time with X-ray photoemission spectroscopy. The temperature-dependent PL spectra revealed that large amount of nonradiative traps were formed with increasing illumination time. The PL intensities, band energies, and bandwidths as well as PL lifetimes of the illuminated CsPbBr3 NC films were analyzed. The experimental results indicated that the PL degradation was attributed to the photo-oxidation of NCs under the illumination.

Colloidal CsPbBr3 perovskite nanocrystal films as electrochemiluminescence emitters in aqueous solutions

Perovskite nanocrystals (NCs), which have emerged as a new class of phosphors with superb luminescence properties and bandgaps that can be easily tuned using chemical methods, have generated tremendous interest for a wide variety of applications where colloidal quantum dots have been very successful as carrier sources. In this study, self-assembled films of CsPbBr3 NCs were produced via drop casting of colloidal NCs onto glassy carbon electrodes (GCEs) to form an NC film-modified electrode. The possible fabrication process of the CsPbBr3 NCs films was discussed. We further studied the anodic electrochemiluminescence (ECL) behavior of the perovskite CsPbBr3 NCs film using cyclic voltammetry with tripropylamine (TPA) as a coreactant, and a possible ECL mechanism was proposed. Briefly, TPA was oxidized to produce strongly reducing radical species, which can react with electrochemically oxidized CsPbBr3 NCs to generate excited CsPbBr3 NCs* capable of light emission. The relative stability of the ECL emission of the CsPbBr3 NC films under aqueous conditions was also investigated, and it was found that they showed operational stability over the first three hours, indicating suitable reliability for application as sensing materials. The results suggested that semiconducting perovskite NCs have great potential for application in the ECL field.

Enhancing the Performance and Stability of Perovskite Nanocrystal Light‐Emitting Diodes with a Polymer Matrix

All‐inorganic perovskite nanocrystal materials exhibit excellent light‐emitting properties in the visible range with narrow‐band emissions, relatively high stability levels, and high photoluminescence quantum efficiency. A uniform morphology of perovskite nanocrystal film is necessary to realize highly efficient light‐emitting devices, but the morphology of CsPbX3 nanocrystal films has not been intensively studied. Here, a novel method is presented to obtain uniform and stable CsPbBr3 nanocrystal film through a drop‐casting method with a poly(methyl methacrylate) (PMMA) matrix. The introduction of CsPbBr3 nanocrystal:PMMA composite film into a perovskite nanocrystal light‐emitting diode (PeNLED) brings enhanced device performance with good coverage of green electroluminescence (EL) emission. Moreover, the long‐term stability of the PeNLED is improved by the presence of the PMMA due to the resulting considerable water resistance and good thermal stability. Much less EL blinking is also observed from PeNLEDs with the CsPbBr3 nanocrystal:PMMA composite film as compared to the amount with perovskite bulk film under a continuous bias condition. Therefore, it is emphasized that the enhanced efficiency and stability of PeNLEDs by the CsPbBr3 nanocrystal:PMMA composite film can further promote their usage in displays and in lighting applications.