CsPbI3 Quantum Dots Research Articles

Color adjustable CsPbX3 (X=Cl, Br, I) perovskite quantum dots germanate glass

CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) have attracted extensive attention due to their great application prospects in the photoelectronic field. However, the poor long-term stability still limits their practical use. In this work, a whole series of CsPbX3 QDs were precipitated in a germanate glass matrix by a melt quenching method. The emission wavelength can be tunable in the entire visible spectral region by adjusting of the halide ions and the thermal treatment process. The photoluminescence quantum yield of CsPbBrxI3-x QDs glass can reach up to 38.24%. The exciton binding energies of CsPbBrxCl3-x, CsPbBr3 and CsPbI3 QDs glass are about 67 meV, 160 meV and 290 meV, respectively. Additionally, the influence of the thermal treatment temperature on photoluminescence properties of CsPbBrxI3-x QDs glass was investigated in detail. These results will be of benefitting to their practical applications, such as display devices and WLEDs.

Ultrathin Dimethylammonium Iodide Matrix: Suppressing Octahedral Distortion and Reconstructing Surface Ligands for Efficient CsPbI3 Quantum Dot Photovoltaics

Inorganic CsPbI3 quantum dots (QDs) have received increasing attention for their application in new‐generation solar cells. However, their poor phase stability due to the small ionic radius of Cs and their inhomogeneous energy landscape on the QD surface during ligand exchange remain as bottlenecks for the practical application of CsPbI3 QD photovoltaics. Herein, the unfavorable octahedral distortion is effectively suppressed by riveting dimethylammonium hydroiodide (DMAI) into the lattice structure. Moreover, DMAI reconstructs the surface ligands to create an ultrathin matrix that encloses the QDs. The ultrathin DMAI matrix effectively passivates the vacancy defects and allows efficient coupling and charge transport in the QD films. As a result, the CsPbI3 QD solar cell yields an efficiency approaching 15%. In addition, the increase in the Goldschmidt tolerance factor enhances the stability of the octahedral structure, resulting in significantly improved device stability.

Synergistic passivation of high stability CsPb(Br/I)3 perovskite quantum dots with double ligands for WLEDs

The all-inorganic perovskite CsPbI3 quantum dots are difficult to achieve pure red stable luminescence due to their poor lattice thermodynamic stability and non-radiative recombination loss caused by surface halide vacancies. Therefore, the pure red perovskites are usually achieved by mixing the composition of halides (Br and I). In this work, CsPb(Br/I)3 quantum dots (QDs) were synthesized by the hot-injection method under the synergistic effect of homophthalic acid (HA), 2-bromoethanesulphonic acid sodium salt (SBES), and oleylamine (OAm). By adjusting the molar ratio of passivates, the synergistic effect of multiple ligands can not only passivate the unliganded Pb2+-related defects on the surface of NCs, but also increase the formation energy of halide vacancies. Meanwhile, due to the bidentate structure of HA, smaller size of perovskites nanocrystals were obtained. Eventually, synergistic boost in device performance is achieved for color-by-blue white light-emitting diodes (WLEDs) with CIE coordinates of (0.3319, 0.3297) and have an external quantum efficiency (EQE) of 10.13%. This strategy paves an efficient way for improving the efficiency and stability of CsPb(Br/I)3 NCs.

Controllable Black-to-Yellow Phase Transition by Tuning the Lattice Symmetry in Perovskite Quantum Dots.

The black-to-yellow phase transition in perovskite quantum dots (QDs) is more complex than in bulk perovskites, regarding the role of surface energy. Here, with the assistance of in situ grazing-incidence wide-angle and small-angle X-ray scattering (GIWAXS/GISAXS), distinct phase behaviors of cesium lead iodide(CsPbI3 ) QDfilms under two different temperature profiles-instant heating-up (IHU) and slow heating-up (SHU) is investigated. The IHU process can cause the phase transition from black phase to yellow phase, while under the SHU process, the majority remains in black phase. Detailed studies and structural refinement analysis reveal that the phase transition is triggered by the removal of surface ligands, which switches the energy landscape. The lattice symmetry determines the transition rate and the coexistence black-to-yellow phase ratio. The SHU process allows longer relaxation time for a more ordered QD packing, which helps sustain the lattice symmetry and stabilizes the black phase. Therefore, one can use the lattice symmetry as a general index to monitor the CsPbI3 QD phase transition and finetune the coexistence black-to-yellow phase ratio for niche applications.

Guanidium iodide treatment of size-controlled CsPbI3 quantum dots for stable crystal phase and highly efficient red LEDs

The optoelectronic properties of lead-halide perovskite quantum dots (QDs) can be tuned according to their halogen composition ratio and quantum size effect. However, the pure red emission of CsPbI3 QDs exhibits poor phase stability, thereby resulting in a phase transition to a nonphotoactive yellow phase at room temperature. These phase instabilities are accompanied by crystal strain and instability of the QD surface, which induce ion diffusion and desorption. Herein, we demonstrate the precise size control and postsynthetic guanidinium iodide (GAI) treatment to stabilize the crystal phase of CsPbI3 QDs. These synergistic effect results in higher ambient photoluminescence stability and photostability than those of pristine QDs. More importantly, the CsPbI3 QD light-emitting diodes achieve excellent external quantum efficiency of 22.5% and longer operational stability of over 10 h by the synergy effect of QD size control and GAI treatment.

In Situ Iodide Passivation Toward Efficient CsPbI3 Perovskite Quantum Dot Solar Cells

HighlightsThe introduction of hydroiodic acid (HI) manipulates the dynamic conversion of PbI2 into highly coordinated species to optimize the nucleation and growth kinetics.The addition of HI enables the fabrication of CsPbI3 perovskite quantum dots with reduced defect density, enhanced crystallinity, higher phase purity, and near-unity photoluminescence quantum yield.The efficiency of CsPbI3 perovskite quantum dot solar cells was enhanced from 14.07% to 15.72% together with enhanced storage stability.All-inorganic CsPbI3 quantum dots (QDs) have demonstrated promising potential in photovoltaic (PV) applications. However, these colloidal perovskites are vulnerable to the deterioration of surface trap states, leading to a degradation in efficiency and stability. To address these issues, a facile yet effective strategy of introducing hydroiodic acid (HI) into the synthesis procedure is established to achieve high-quality QDs and devices. Through an in-depth experimental analysis, the introduction of HI was found to convert PbI2 into highly coordinated [PbIm]2−m, enabling control of the nucleation numbers and growth kinetics. Combined optical and structural investigations illustrate that such a synthesis technique is beneficial for achieving enhanced crystallinity and a reduced density of crystallographic defects. Finally, the effect of HI is further reflected on the PV performance. The optimal device demonstrated a significantly improved power conversion efficiency of 15.72% along with enhanced storage stability. This technique illuminates a novel and simple methodology to regulate the formed species during synthesis, shedding light on further understanding solar cell performance, and aiding the design of future novel synthesis protocols for high-performance optoelectronic devices.

Atomically Unraveling the Structural Evolution of Surfaces and Interfaces in Metal Halide Perovskite Quantum Dots.

Revealing the local structural change of metal halide perovskites (MHPs) induced by external conditions is important to understand its performance and stability in optoelectronic applications. However, previous studies on the properties and structures of MHPs are usually limited by the spatial resolution of the probe, and it is still challenging to obtain its atomic structural information in real space. In this work, the integrated differential-phase-contrast scanning transmission electron microscopy is applied to the low-dose imaging of CsPbI3 quantum dots (QDs). In particular, the local structures in QDs, such as surfaces and interfaces, can be atomically resolved. Then, the structural evolution of CsPbI3 QDs under various external conditions can be unraveled during in situ heating or ex situ treatments, where it lose cubic shapes and fuse to larger particles. The changes in surfaces and interfaces with missing Cs ions and PbI6 octahedrons can be semi-quantitatively studied by profile analysis and bond-length measurement in images. Finally, density functional theory calculations are performed to illustrate the properties and stabilities of the different structures that are observed. These results provide atomic-scale insights into the structural evolution of QDs, which is of great importance to modify the performance of perovskite materials and devices.

Surface Vertical Multi-Emission Laser with Distributed Bragg Reflector Feedback from CsPbI3 Quantum Dots.

Quantum dots (QDs) laser has become an important way to solve micro-application problems in many fields. However, single wavelength distributed Bragg reflector (DBR) has many limitations in practical applications, such as signal transmission. How to realize multiwavelength DBR lasing output simply is a challenge. To achieve a stable multi-wavelength quantum dots laser in the near-infrared region, the perovskite CsPbI3 QDs laser with DBR structure is developed in this paper. A tetragonal crystal structure with complete bonding information and no defect is explained by X-ray diffractions (XRD) and Raman spectrum. The cross-section morphology of the DBR laser and the surface morphology of QDs is measured by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. An elliptical light propagation field and a double wavelength laser radiation are obtained from the finite-difference time-domain (FDTD) simulation. The output of the three wavelength lasers at 770 nm, 823 nm, and 873 nm is measured. The emission time of a DBR laser is about 2 h, and the average fluorescence quantum yield is 60%. The cavity length selection and energy level model are put in place to clearly see the working mechanism. All the results suggest that an effective and stable CsPbI3 quantum dots DBR laser is realized.

Spectrally Stable Pure Red CsPbI3 Quantum Dots Light‐Emitting Diodes via Effective Low Temperature Gradient Centrifugation Separation and Surface Modification

AbstractDevelopment of high‐performance and stable pure red perovskite light‐emitting devices (LEDs) promotes commercialization of perovskite. Benefiting from the quantum confinement effect, pure red CsPbI3 quantum dots (QDs) can avoid the color drift issue for mixed halide systems. Herein, a facile temperature‐dependent hot‐injection method combined with low temperature gradient centrifugation is employed to prepare 5.60 ± 0.05 nm pure red QDs. The QDs exhibit 642 nm photoluminescence (PL) with 37 nm full width at half maximum, and their Commission Internationale de l'Eclairage (CIE) coordinates located at (0.708, 0.292) match well with standard pure red for Rec. 2020. The PL half‐lifetime for pure red QDs solution is 210 days under ambient conditions, and both the X and Y coordinates of CIE only fluctuate within (0.002, 0.002). Finally, a simple NH4I post‐treatment to decrease ligand length further boosts the QDs conductivity, and the pure red LED exhibits 9.4% maximum external quantum efficiency. The electroluminescence spectra exhibits a sharp peak at 645 nm, and their CIE coordinates are located at (0.707, 0.290). Furthermore, the pure red LED exhibits both good working and color stability. Its half‐lifetime is 25.1 min and color drifts are only (0.002, 0.002) after 30.0 min of continuous working at 60 cd m−2 with a constant current density of 3.5 mA cm−2.

Whispering gallery mode micro-lasing in CsPbI3 quantum dots coated on TiO2 microspherical resonating cavities.

Whispering gallery mode (WGM) lasing in CsPbI3 quantum dots (QDs) coated on TiO2 spherical microcavities is demonstrated. The photoluminescence emission from a CsPbI3-QDs gain medium strongly couples with a TiO2 microspherical resonating optical cavity. Spontaneous emission in these microcavities switches to a stimulated emission above a distinct threshold point of 708.7 W/cm2. Lasing intensity increases three to four times as the power density increases by one order of magnitude beyond the threshold point when the microcavities are excited with a 632-nm laser. WGM microlasing with quality factors as high as Q∼1195 is demonstrated at room temperature. Quality factors are found to be higher for smaller TiO2 microcavities (∼2 µm). CsPbI3-QDs/TiO2 microcavities are also found to be photostable even after continuous laser excitation for 75 minutes. The CsPbI3-QDs/TiO2 microspheres are promising as WGM-based tunable microlasers.

Suppressing Ion Migration of Mixed‐Halide Perovskite Quantum Dots for High Efficiency Pure‐Red Light‐Emitting Diodes

AbstractPerovskite‐based light‐emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the “pure red” emission, i.e., in the 620–650 nm range, required for high‐definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI3‐xBrx quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI3 QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1‐dodecanethiol (1‐DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure‐red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m−2, and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half‐life of 70 min at an initial luminance of 150 cd m−2.

Origin of the bias instability in CsPbI3 light-emitting diodes

With the rapid development of all-inorganic CsPbX3 (X = I, Br, and Cl) perovskite light-emitting diodes (PeLEDs), their external quantum efficiency (EQE) has made great progress in the last few years. However, severe performance degradation at the operation condition impedes its large-scale industrial application. In this text, by using the advanced spherical aberration corrected transmission electron microscope (TEM), the degradation pathway of PeLEDs under bias loading was more systematically and comprehensively, especially from the viewpoint of its microstructural evolution pathway, which showed that iodine vacancy migration triggered the structural collapse was the primary inducement of performance decay. To solve this problem, inorganic termination ZnI2 was employed to passivate the surface halide vacancy defects and supplement the halide ion into the lattice, which significantly improves the photoluminescence (PL) lifetime and stability of CsPbI3 quantum dots (QDs). As expected, not only the EQE of PeLEDs has been greatly improved, but also the operating half-lifetime is enhanced by about 4 times as compared with the original one. Microstructural characterization and density functional (DFT) calculations confirm that the preferential segregation of Zn element on the surface of QDs was the principal cause to passivate the defect state of QDs, which exhibits lower formation energy and better operational stability.

Colored Daytime Radiative Cooling Textiles Supported by Semiconductor Quantum Dots

Radiative cooling, a zero-energy, eco-friendly cooling technology, has attracted tremendous attention recently for its potential of fighting global warming and climate changes. Radiative cooling fabrics with diffused solar reflections typically have reduced light pollution and can be mass-produced with currently available techniques. However, the monotonous white color has hindered its further applications and no colored radiative cooling textiles are available yet. In this work, we electrospun PMMA textiles containing CsPbBrxI3-x quantum dots as the colorant to achieve colored radiative cooling textiles. A theoretical model to predict the 3D color volume and cooling threshold was proposed for this system. As indicated by the model, a sufficiently high quantum yield (>0.9) will guarantee a wide color gamut and strong cooling ability. In the real experiments, all of the fabricated textiles show excellent color agreement with the theory. The green fabric containing CsPbBr3 quantum dots achieved a subambient temperature of ∼4.0 °C under direct sunlight with an average solar power density of 850 W/m2. The reddish fabric containing CsPbBrI2 quantum dots also managed to cool 1.5 °C compared to the ambient temperature. The fabric containing CsPbI3 quantum dots failed to achieve subambient cooling with a slightly increased temperature. Nevertheless, all of the fabricated colored fabrics outperformed the regular woven polyester fabric when placed on a human hand. We believed that the proposed colored textiles may widen the range of applications for radiative cooling fabrics and have the potential to become the next-generation colored fabrics with stronger cooling ability.

Photomultiplication‐Type Organic Photodetectors with High EQE‐Bandwidth Product by Introducing a Perovskite Quantum Dot Interlayer

AbstractA photomultiplication (PM)‐type organic photodetector (OPD) that exploits the ionic motion in CsPbI3 perovskite quantum dots (QDs) is demonstrated. The device uses a QD monolayer as a PM‐inducing interlayer and a donor–acceptor bulk heterojunction (BHJ) layer as a photoactive layer. When the device is illuminated, negative ions in the CsPbI3 QD migrate and accumulate near the interface between the QDs and the electrode; these processes induce hole injection from the electrode and yield the PM phenomenon with an external quantum efficiency (EQE) >2000% at a 3 V applied bias. It is confirmed that the ionic motion of the CsPbI3 QDs can induce a shift in the work function of the QD/electrode interface and that the dynamics of ionic motion determines the response speed of the device. The PM OPD showed a large EQE‐bandwidth product >106 Hz with a −3 dB frequency of 125 kHz at 3 V, which is one of the highest response speeds reported for a PM OPD. The PM‐inducing strategy that exploits ionic motion of the interlayer is a potential approach to achieving high‐efficiency PM OPDs.

Interfacial passivation of CsPbI3 quantum dots improves the performance of hole-transport-layer-free perovskite photodetectors

Photodetectors (PDs) suffer from dark current due to defects in the perovskite photosensitive layer. Contact between the photosensitive layer and carbon electrodes could result in recombination of carriers at the interface. In this work, CsPbI3 quantum dots (QDs) were added between the photosensitive layer and the carbon electrode as the interfacial layer to passivate the surface defects of perovskite layer and improve the energy level matching at the interface. The effect of QDs concentrations on the passivation of the perovskite layer was investigated. It was found that the photoluminescence intensity of perovskite films was the strongest and the decay lifetime was the longest when the QDs concentration was 3 mg/mL. Owing to QDs passivation, the dark current of perovskite PD decreased by 94% from 2.04; times ;10^{ - 9} to 1.17; times ;10^{ - 10} A. The responsivity (R) at 605 nm improved by 27% from 0.29 to 0.37 A/W at 0 V bias voltage. The specific detectivity (D*) increased by 420% from 8.9; times ;10^{11} to 4.7; times ;10^{12} Jones.

Revealing Atomic‐Level Surface Passivation of PbI2‐Reconditioned Red Perovskite Quantum Dots

AbstractCsPbI3 perovskite quantum dots (QDs) are promising materials for high‐efficiency and low‐cost red fluorophores in advanced display and light‐sensing applications. However, structural and spectral stabilities of CsPbI3 QDs by traditional preparation are seriously broken in water or light environment. Here, a compositional engineering strategy with an additional PbI2‐recondition process to synthesize highly‐stable CsPbBr1.2I1.8 @ SiO2 QDs is demonstrated. Time‐ and temperature‐dependent photoluminescence and Raman measurements prove that spectral stability and exciton binding energy of QDs are greatly improved within this strategy. Notably, high‐resolution structure characterizations, point‐to‐point diffraction patterns and line‐scanning of element distributions provide strong and direct evidence at atomic‐level to reveal that PbI2‐recondition can repair defects well, which helps to construct perfect lattices and homogeneous SiO2 passivation layers to prevent the surface bonding of molecules. Moreover, our red perovskite QDs are further designed to prepare various anti‐counterfeiting labels as multi‐scale complex patterns to store and protect information. The proposed recondition strategy explores a new avenue to prepare stable and high‐quality red perovskite QDs for new‐generation lighting and light‐sensing devices.

SERS-active plasmonic metal NP-CsPbX3 films for multiple veterinary drug residues detection

Sensitive and multiple veterinary drug residues detection is of important for food safety. Herein, uniform plasmonic Au nanobipyramids@Ag nanorods (Au NBP@Ag NR)-CsPbX3 films with strong surface-enhanced Raman scattering (SERS) activity were constructed. The effects of different CsPbX3 (X = Cl, Br, I, or mixed halogens) quantum dots (QDs) on the SERS performances of plasmonic metal NP films were investigated. CsPbI3 QDs with large dielectric constant could be served as the dielectric media to retard the attenuation of electromagnetic evanescent wave, inducing strong electromagnetic strength for SERS enhancement. Plasmon-induced metal-to-perovskite interfacial charge transfer transition also contributed to SERS enhancement. SERS-active plasmonic Au NBP@Ag NR-CsPbI3 films had excellent sensitivity and high reproducibility for quantitative, accurate and multiple detection of chloramphenicol, diazepam and malachite green in food matrix. This work deepened the understanding of the SERS enhancement mechanisms of plasmonic metal NP-perovskite hybrid heterostructures, showing potential prospects in food safety monitoring.

Ultra-small α-CsPbI3 perovskite quantum dots with stable, bright and pure red emission for Rec. 2020 display backlights.

The synthesis of α-CsPbI3 perovskite quantum dots (QDs) with pure red emission around 630 nm is in high demand for display backlight application. However, the phase transition of α-CsPbI3 to yellow non-emitting δ-CsPbI3 has been proven to be a great challenge for the classic colloidal synthesis route for perovskite QDs in octadecene (ODE). Herein, we report a novel colloidal synthesis route by replacing ODE with lauryl methacrylate (LMA) as the reaction solvent to improve the solubility of precursors, resulting in small sized α-CsPbI3 QDs with a diameter of only 4.2 nm, which are the smallest red PQDs reported so far. The corresponding CsPbI3 QD films exhibit a tunable photoluminescence (PL) emission peak in the bright pure red region of 627 to 638 nm. The CsPbI3 QD polymer composite films with PL emission at 630 nm exhibit a superior photoluminescence quantum yield (PLQY) and photostability to mixed halide CsPbBrI2 films under intense illumination. Perovskite light emitting diodes (LED) with the color gamut reaching 96% of the Rec. 2020 standard are achieved using these films. This study provides a high-performance pure red fluorescent material with a robust, low-cost, and reproducible colloidal chemistry that will pave the way for the adoption of perovskite QDs in display backlight application.

Planar Perovskite Solar Cells Using Perovskite CsPbI3 Quantum Dots as Efficient Hole Transporting Layers.

Perovskite CsPbI3 quantum dots (QDs) were synthesized as a hole-transporting layer (HTL) of a planar perovskite solar cell (PSC). By using the Octam solution during the ligand engineering, CsPbI3 QDs exhibits a denser grain and a larger grain size due to the short-chain ligands of Octam. In addition, CsPbI3 QDs with the Octam solution showed a smooth and uniform surface on MAPbI3 film, indicating the QDs improved the microstructure of the MAPbI3 perovskite film. As a result, the PSC with CsPbI3 QDs as an HTL has the optimal open-circuit voltage as 1.09 V, the short-circuit current as 20.5 mA/cm2, and the fill factor (FF) as 75.7%, and the power conversion efficiency (PCE) as 17.0%. Hence, it is inferred that introducing QDs as a HTL via the ligand engineering can effectively improve the device performance of the PSC.

Achieve high-efficiency long afterglow luminescence control using CsPbI3 quantum dots

The construction of visible full-spectrum tunable afterglow luminescence is of great significance for long afterglow materials. Here we developed a new composite material whose afterglow were continuously tunable from blue to red light, we prepared CsPbI3 quantum dots (QDs) by thermal injection method and added passivators to obtain relatively more stable QDs materials, the SDS-CsPbI3 QDs after passivation treatment was more than twice the photoluminescent (PL) intensity of the original QDs after 10 days, which has a positive effect on the large-scale production and application of all-inorganic perovskite QDs. By uniformly distributing CsPbI3 QDs on the surface of Sr2MgSi2O7:Eu2+,Dy3+(SMS) by Stöber method, a color-tunable long-persistence luminescent material CsPbI3/SMS@SiO2 was prepared, and the tunable afterglow glows from 465 nm to 700 nm was realized by optical conversion. In addition, the PL intensity of the composite material under ultraviolet light is increased by more than 50%, and it can remain stable for a long time; its high temperature resistance is also improved to 140 °C; and the luminous intensity after 10 days remains at a high level. This research also provides new ideas and methods for the development of multicolor long afterglow materials.