- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Enhanced stability and optical absorption in the perovskite‐based compounds MA$_{1‐x}$Cs$_x$PbI$_{3‐y}$Br$_y$
摘要： Organometal halide perovskites have been outstanding from enormous amount of functional materials thanks to their highly cost-effective processability and prominent light harvesting capacity. Unfortunately, poor long-term stability seriously hinders their further development. The recent experimental observations suggest that Cesium is a promising candidate to enhance the stability of MAPbI3. To explore the inherent mechanism, a first-principles investigation based on density functional theory, including hybrid functional, has been performed to analyze the electronic and optical properties of perovskite series MA0.75Cs0.25PbI3-yBry. The results indicate that perovskite compound MA0.75Cs0.25PbI2Br is significantly superior to the other doped series in terms of optical absorption within the visible-light range. In the meanwhile, both Bader charge analysis and charge density distribution show that the compound of MA0.75Cs0.25PbI2Br is the most stable among all the doped perovskite series. Moreover, it is clearly manifested that the impact of cesium is mainly embodied in the enhancement of the stability rather than in the improvement of optical absorption. Our study sheds a new light on screening new-type light harvesting materials, and provides theoretical insight into the rationale design of highly efficient and stable photovoltaic devices based on these functional materials.
关键词： optical absorption,stability,first-principles calculations,perovskite compounds
更新于2025-09-23 15:23:52
-
Disentangling topographic contributions to near-field scanning microwave microscopy images
摘要： We develop empirical models to predict the contribution of topographic variations in a sample to near-field scanning probe microwave microscopy (NSMM) images. In particular, we focus on |S11| images of a thin Perovskite photovoltaic material and a GaN nanowire. The difference between the measured NSMM image and this prediction is our estimate of the contribution of material property variations to the measured image. Prediction model parameters are determined from either a reference sample that is nearly free of material property variations or directly from the sample of interest. The parameters of the prediction model are determined by robust linear regression so as to minimize the effect of material property variations on results. For the case where the parameters are determined from the reference sample, the prediction is adjusted to account for instrument drift effects. Our statistical approach is fully empirical and thus complementary to current approaches based on physical models that are often overly simplistic.
关键词： Near-field scanning probe microwave microscopy,Signal extraction,GaN nanowire,Statistical methods,Perovskite materials,Atomic force microscopy
更新于2025-09-23 15:23:52
-
Blue Electrogenerated Chemiluminescence from Halide Perovskite Nanocrystals
摘要： Electrogenerated chemiluminescence (ECL) has been extensively used in ultrasensitive electroanalysis because it can be generated electrochemically without using expensive optics and light sources. Visible ECL emission can be obtained with a reasonable quantum yield and stability. Blue ECL is rare and often suffers from stability and poor quantum efficiency. Blue ECL emission at 473 nm from organometallic halide perovskite nanocrystals (PNCs), CH3NH3PbCl1.08Br1.92, is reported here for the first time using tripropylamine (TPrA) as co-reactant. The blue ECL emission peak resembles its photoluminescence peak position. In addition to this blue emission peak, the ECL spectra of CH3NH3PbCl1.08Br1.92 PNCs also showed a broad ECL peak at 745 nm. Generation of the second ECL peak at 745 nm from CH3NH3PbCl1.08Br1.92 PNCs was can be explained by the existence of surface trap states on as-synthesized PNC due to incomplete surface passivation. Halide anion tunability of ECL emission from CH3NH3PbX3 (X: Cl, Br, I) PNCs is also demonstrated. The fluorescence microscopy image of single PNC and stability of selected single PNCs are presented in this with simultaneous acquisition of fluorescence spectra using 405-nm laser excitation. The photoluminescence (PL) decay was described by PL lifetime (τ) of 1.2 ns. The effect of the addition of surfactants (oleic acid and n-octylamine) on the fluorescence intensity and stability of CH3NH3PbCl1.08Br1.92 PNCs is also discussed.
关键词： Surfactants,Blue light emission,ECL (electrogenerated chemiluminescence),Photoluminescence (PL),Perovskite nanocrystals (PNCs),Photoluminescence quantum yield (PLQY)
更新于2025-09-23 15:23:52
-
Artifacts in Transient Absorption Measurements of Perovskite Films Induced by Transient Reflection from Morphological Microstructures
摘要： Organolead halide perovskites MAPbX3 (MA = CH3NH3+; X = Cl?, Br?, I?) have attracted broad tremendous interest in the past 10 years for applications in solar cells and light-emitting devices. In evaluating the quality of the perovskite materials, spectroscopic characterizations such as static and time-resolved absorption and photoluminescence measurements are essential to examine their photophysical properties. A recent report found that the correct measurement of static absorption spectra of MAPbX3 films is indeed difficult due to the strong light scattering caused by their poor surface coverage or complex microstructures. These morphological complexities seem to be inevitable in thin-film fabrication and should not only affect the steady-state spectroscopic measurements but also can significantly impact the time-resolved spectroscopic characterizations, whose results are crucial for understanding photoinduced carrier dynamics in the examined materials. Photoexcited states in semiconductor materials induce changes in the real and imaginary parts of the dielectric function. This leads to changes in absorption (imaginary part) and reflectivity (real part), which can be substantial for materials with significant values of refractive index such as lead halide perovskites. Transient absorption (TA) spectroscopy is a typical technique that has been broadly used to probe photoexcited state dynamics in perovskites and other semiconductor materials. In TA measurements, a pump laser pulse is used to excite the perovskite films, and the induced absorption changes (ΔA) are recorded as a function of both wavelength and time. With the transmitted light as the probe (Figure 1a), the TA signal (ΔA) is mainly decided by the ratio of the intensity of transmitted probe light with and without pump excitation (see eq S1 in the SI), assuming that the loss of transmitted probe light completely results from the sample absorption. On the basis of the same experimental setup, transient reflection (TR) measurements can also be carried out by using the reflected probe light as detection signal (Figure 1b). The TR signal (ΔR/R) can also be determined by the ratio of the intensity of reflected probe light with and without pump excitation (see eq S4 in the SI). Unlike the TA measurements that mainly probe the bulk property of samples, the TR signal mainly detects the photoinduced reflection variations due to the refractive index change at the sample surface. Therefore, the TR spectrum and kinetics can be significantly different from those of TA even in the same sample. For example, previous TA and TR measurements have found dramatically faster carrier recombination kinetics on the surface than in the bulk of MAPbX3 perovskite films or single crystals because of the presence of more surface defects. There is an abnormal case in the regular TA measurements particularly when performed on the films with large and heterogeneous microstructures (e.g., films with poor coverage, large grains, and pinholes) because the loss of transmitted probe light in their TA measurements likely results not only from the sample absorption but also from the reflection of the film surface or the boundary of microstructures in samples. In this case, the measured transient spectrum, though collected in the transmittance mode as in TA, can contain contributions from both TA and TR signals (see Figure 1c and eq S6 in the SI). This could lead to distorted TA spectra and thus inaccurate analysis of photoinduced kinetics. A solution-processed organic or inorganic halide perovskite thin film is a typical material whose morphological microstructures were found to have significant impact on device performance. Although the photoinduced carrier dynamics in perovskite films has been extensively studied using TA spectroscopy, the possible artifacts in TA results induced by TR signal originating from the photoinduced reflectivity variation of film surfaces and microstructures have been overlooked. Herein, in order to clarify the influence of TR signal in the regular TA measurements, we performed a careful transient spectroscopic analysis on a series of MAPbBr3 perovskite films with different microstructure morphology. Meanwhile, TR measurements on MAPbBr3 single crystals (SCs) were carried out for comparison. We confirmed that the TA spectra measured in MAPbBr3 perovskite films with large and heterogeneous microstructures do comprise non-negligible TR signals from the photoinduced reflection of microstructures, with the weight of contribution increased from ～20 to ～100% as the size of the microstructure increased from <200 nm to 1?2 μm. The presence of TR signal leads to an “artifact” feature in the TA spectra and faster observed kinetics owing to the faster surface carrier recombination, which will thus mislead the analysis of bulk carrier dynamics. We also provided a method to reduce the TR signal in actual TA measurements by adding solvent with its refractive index close to the samples, by which the TR distortion can be suppressed to some extent.
关键词： artifacts,transient reflection,transient absorption,carrier dynamics,perovskite films,microstructures
更新于2025-09-23 15:23:52
-
Perovskite photocatalyst CsPbBr3-xIx with a bandgap funnel structure for H2 evolution under visible light
摘要： A simple and efficient light-assisted method is employed to prepare powder samples of all-inorganic mixed-perovskite CsPbBr3-xIx from CsPbBr3 by ion exchange in aqueous HBr/KI solution such that the concentration of I in a sample particle decreases on going from the surface to the interior. CsPbBr3-xIx/Pt, namely, CsPbBr3-xIx samples loaded with Pt nanoparticles, shows a high performance for the hydrogen evolution under visible-light irradiation in aqueous HBr solution saturated with CsPbBr3. The H2 evolution rate of the CsPbBr3-xIx/Pt powders (200 mg) is determined to be 224 μmol h-1, under 120 mW cm-2 visible-light (λ ≥ 420 nm) illumination. The CsPbBr3-xIx samples have a high stability, with no apparent decrease in the catalytic activity after 50 h of repeated H2 evolution experiments. The apparent quantum efficiency of CsPbBr3-xIx/Pt is determined to be 2.15% under the irradiation of 450 nm light.
关键词： photocatalysis,hydrogen evolution,bandgap funnel,all-inorganic perovskite,halide gradient
更新于2025-09-23 15:23:52
-
Alternative Type 2D-3D Lead Halide Perovskite with Inorganic Sodium Ions as Spacer for High Performance Light Emitting Diodes
摘要： Two-dimensional (2D) lead halide perovskites with long-chain ammonium halides display high photoluminescence quantum yield (PLQY), due to their size and dielectric confinement, which promise a high efficiency and low-cost light emitting diode (LED). However, the presence of insulating organic long-chain spacer cation (L) dramatically deteriorates the charge transport properties along the out-of-plane nanoplatelet direction or adjacent nanocrystals, which would limit the LED device performance. In order to overcome this issue, we successfully incorporate small alkaline ions such as sodium (Na+) to replace long organic molecule. Grazing incident X-ray diffraction (GIXRD) measurements verify the 2D layered formation with preferential crystallite orientation. In addition, the incorporated sodium salt also generates amorphous sodium lead bromide (NaPbBr3) in perovskite as spacers to form nanocrystal-like halide perovskite film. PLQY is dramatically improved in the sodium incorporated film associating with enhanced PL lifetime. With incorporating small concentration of an organic additive, this 2D-3D perovskite can achieve a compact and uniform film. Therefore, a 2D-3D perovskite achieves a high external quantum efficiency (EQE) of 15.9% with good operational stability. Our work develops a type of 2D-3D halide perovskite with various inorganic ions as spacers for high performance of promising optoelectronic devices.
关键词： two-dimensional,alkaline halide,perovskite,dielectric confinement,light-emitting diode
更新于2025-09-23 15:23:52
-
Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking
摘要： Direct exposure to ultraviolet (UV) light is closely related to various harmful effects [1-3], ranging from skin injures to cancer originated from DNA damage. Recent years, some studies reported that blue light are also detrimental to humans [4,5], for example, the blue light could cause photochemical lesions to human retinal within the intensity range of the natural light [6]. Furthermore, blue light is responsible for the solar retinitis and may play a role in age-related macular degeneration. Importantly, the harmful effects of blue lights generated from the electronic display devices should also be careful [7]. Thus, the development of new UV and blue light shielding materials has been received much attention [8]. In the past few years, there has been an increased awareness of the importance to develop UV shielding materials. A variety of materials have been used to prevent UV lesions. Organic molecules like avobenzone or oxybenzone have been used as a UV absorber for many years, but the self-degradation limits their usage time. Inorganic materials such as zinc oxide (ZnO) and titanium oxide (TiO2) have been used intensively for UV shielding [9-12]. However, photocatalytic properties and self-degradations of the ZnO and TiO2 based absorbers also hindered their applications [13,14]. Other materials, e.g., graphene oxide-poly(vinyl alcohol) composite film and lanthanide complex functionalized cellulose nanopaper were also reported for UV shielding [15,16]. Whereas, the excellent UV-filtering capability of these films was obtained by sacrificing the visible light transmittance. Therefore, fabricating UV and blue light blocking materials with good photostability and high transparency to the rest of visible light still remains a challenge and is urgently needed to be developed. Recently, because of the outstanding performance in photovoltaic applications, lead halide perovskite APbX3 (where A = CH3NH3+, (NH2)2CH+ and Cs+, X = Cl?, Br? and I?) has become the most noticeable materials [17-22]. These perovskite nanocrystals exhibit intriguing features [23], such as easy tunable band gap, sharp optical absorption edges and high quantum efficiency with narrow emission spectra. These nanocrystals have been studied extensively for various optical applications, especially light emitting diodes and lasers [24-27]. Post modification of perovskite nanocrystals by anion exchange enables the absorbance band gap tuned from ultraviolet to near infrared spectra [28,29]. In addition, the perovskite nanocrystals show large absorption range, which offers the great potential for UV and blue light shielding applications. Although the tunable absorption-band edge of perovskite nanocrystals has already been realized, there have not been reports on developing UV and blue light blocking material with tunable absorption-band edge. Herein, we aim to the development of a simple and easy way to fabricate UV and blue light blocking material by mixing pervoskite nanocrystals and ethyl cellulose (EC). In this study, EC was used as a host material for the CsPb(Cl/Br)3 pervoskite nanocrystals. By tuning the ratio of Br to Cl, the blocked wavelength range could be easily controlled. Using the sharp absorption edges, the material possesses excellent light blocking ability in the range of 200-460 nm and maintains high transparency (95%) to visible light in the range beyond blue light.
关键词： UV blocking,Cesium lead halide nanocrystals,Blue light blocking,Tunable adsorption edge,Perovskite nanocrystals
更新于2025-09-23 15:23:52
-
Structure variation and luminescence enhancement of BaLaMg(Sb, Nb)O6:Eu3+ double perovskite red phosphors based on composition modulation
摘要： A series of BaLaMgSb1-xNbxO6:Eu3+ double perovskite red phosphors was successfully obtained. X-ray diffraction and Rietveld refinement analyses were conducted to determine the phase information and the detailed structure parameters. The coordinate variations of both La3+/Eu3+ and Sb5+/Nb5+ were discussed to elucidate the influence of B-site ion doping on the lattice variation. Luminescence properties, excitation and emission spectra, were presented to show the advantages of doping with Nb5+ ion. Ultraviolet-vis diffuse reflectance spectra were performed to reveal the reason for the decreased emission intensity under the charge transfer band excitation. Moreover, band gap energy was estimated to clarify the relationship between the increased intensity (λex = 395 and 465 nm) and Nb5+ concentration. Intensity ratios of I(615)/I(590) were performed to show the symmetry variation of the lattice. Thermal quenching property was also investigated and the quenching mechanism was discussed in detail based on the ionization process.
关键词： White LED,Structure variation,Thermal quenching mechanism,Double perovskite
更新于2025-09-23 15:23:52
-
Morphological regulation of all-inorganic perovskites for multilevel resistive switching
摘要： Enormous attention has been paid to all-inorganic cesium lead halide perovskites in various photoelectronic fields for their remarkable performances. However, comparing to their analogue organic-inorganic hybrid perovskites, the film morphology of such all-inorganic lead halide perovskites is difficult to control due to the low solubility of cesium salt. Here, we propose a new fabrication routine to control the film morphology of CsPbBr3. A series of CsPbBr3 thin films with big grains (≈800 nm) were successfully prepared. The memristors based on such CsPbBr3 thin films take on typical bipolar resistive switching behavior and remarkable characteristics such as high Ron/Roff ratio (≈105), very low working voltage (≈ ± 1 V), and long data retention (≥104 s). Furthermore, through modulating the film morphology, memristors with multilevel resistive switching behavior can be easily prepared. These advantages demonstrate that the all-inorganic cesium lead halide memristors possess great potential for future application.
关键词： Memristor,Morphological regulation,Multilevel resistive switching,All-inorganic perovskite
更新于2025-09-23 15:23:52
-
Electronic and optical properties of double perovskite oxide Pb2ScMO6 (M = Ta, Sb) using a first principles approach
摘要： In this study, the electronic and optical properties of the double perovskite (DP) oxides Pb2ScMO6 (M = Sb, Ta) were systematically investigated using the full-potential linearized augmented plane wave model. Calculations were performed using both the generalized gradient approximation and modified Becke–Johnson potentials. The results showed that the O-atom is responsible for the maxima in the density of states (DOS) in the valence band, whereas the Sc-atom contributes to the maximum DOS in the conduction band. The dielectric constants, absorption coefficients, and reflectivity were also calculated for these systems. The results indicated the presence of wide band gaps in both of these DPs, thereby indicating their insulating semiconducting nature.
关键词： photon energy,energy,dielectric,double perovskite,density of states,band gap
更新于2025-09-23 15:23:52