Inorganic Perovskite Quantum Dots Research Articles

Morphology-Dependent Charge Carrier Dynamics and Ion Migration Behavior of CsPbBr3 Halide Perovskite Quantum Dot Films.

Exceptional electronic, optoelectronic, and sensing properties of inorganic Cs-based perovskites are significantly influenced by the defect chemistry of the material. Although organic halide perovskites that have a polycrystalline structure are heavily studied, understanding of the defect properties at the grain boundaries (GB) of inorganic Cs-based perovskite quantum dots (QDs) is still limited. Here, morphology-dependent charge carrier dynamics of CsPbBr3 quantum dots at the nanoscale by performing scanning probe microscopy of thermally treated samples are investigated. The grain boundaries of defect-engineered samples show higher surface potential than the grain interiors under light illumination, suggesting an effective role of GBs as charge collection and transport channels. The lower density of crystallographic defects and lower trap density at GBs specifically of heat-treated samples cause insignificant dark current, lower local current hysteresis, and higher photocurrent, than the control samples. It is also shown that the decay rate of surface photovoltage of the heated sample is quicker than the control sample, which implies a considerable impact of ion migration on the relaxation dynamic of photogenerated charge carriers. These findings reveal that the annealing process is an effective strategy to control not only the morphology but also the optoelectrical properties of GB defects, and the dynamic of ion migration. Understanding the origin of photoelectric activity in this material allows for designing and engineering optoelectronic QD devices with enhanced functionality.

Passivation of Surface Defects by X-type Short-Chain Ligands for High Quantum Yield and Stable CsPbX3 Quantum Dots Synthesis and Application in WLEDs

All-inorganic CsPbX3 perovskite quantum dots have excellent optoelectronic properties and are excellent candidates for optoelectronic applications. However, the surface ligands (oleyl ammonium, oleic acid) commonly used in traditional inorganic perovskite quantum dots easily fall off from the quantum dots and their protective power is relatively weak, resulting in poor quantum yield and stability of the quantum dots, limiting their application. In this paper, we introduce an X-type short-chain ligand (DDEAB) passivation strategy to enhance the optoelectronic properties of CsPbX3 quantum dots through a facile room-temperature synthesis method and the strong affinity of X-type ligands for surface atoms. The results of TRPL and X-ray photoelectron spectroscopy showed longer lifetime and stronger surface affinity. This result confirms that didecyldimethylammonium bromide (DDEAB) has better binding to CsPbBr3 QDs and can effectively reduce surface defects and improve quantum yield. As a result, the introduction of short-chain ligands can more effectively passivate the surface halogen defects of CsPbX3 QDs, achieving high quantum yield (>90%) and long-term storage environmental stability. In addition, DDEAB-passivated CsPbBr3 QDs have been successfully applied in white light emitting diodes (WLEDs) with wider color gamut (123%), and good EL stability compared to NTSC TV color standard. Our proposed short-chain ligand DDEAB passivation strategy may provide a reference guideline for the preparation of quantum dots and photovoltaic devices with high photoluminescence and environmental stability.

Interplay of Purcell effect and extraction efficiency in CsPbBr3 quantum dots coupled to Mie resonators.

Inorganic halide perovskite quantum dots have risen in recent years as efficient active materials in numerous optoelectronic applications ranging from solar cells to light-emitting diodes and lasers, and have lately been tested as quantum emitters. Perovskite quantum dots are often coupled to photonic structures either to enhance their emission properties, by accelerating their emission rate thanks to the Purcell effect, or to increase light extraction. From a theoretical point of view, the first effect is often considered at the single-dipole level while the latter is often treated at the mesoscopic level, except possibly for quantum emitters. In this work we employ a layer of perovskite quantum dots coupled to dielectric Mie resonators to exploit both effects simultaneously and achieve an 18-fold increase in luminescence. Our numerical simulations, combined with spatially- and time-resolved photoluminescence measurements, reveal how the macroscopic response of the perovskite-on-Mie resonator structure results from the interplay of the two effects averaged over the whole spatial distribution of emitters. Our work provides thus guiding principles for maximizing the output intensity of quantum emitters embedded into photonic resonators as well as classical emitters integrated in perovskite-based optoelectronic devices.

Highly efficient CsPbBr3@glass@polyurethane composite film as flexible liquid crystal display backlight.

Inorganic lead halide perovskite quantum dots (CsPbX3 QDs (X = Cl, Br, or I)) have attracted more and more attention due to their high absorption coefficient, narrow emission band, high quantum efficiency, and tunable emission wavelength. However, CsPbX3 QDs are decomposed when exposed to bright light, heat, moisture, etc., which leads to severe luminous attenuation and limits their commercial application. In this paper, CsPbBr3@glass materials were successfully synthesized by a one-step self-crystallization method, including melting, quenching and heat treatment processes. The stability of CsPbBr3 QDs was improved by embedding CsPbBr3 QDs into zinc-borosilicate glass. Then, the CsPbBr3@glass was combined with polyurethane (PU) to form a flexible composite luminescent film CsPbBr3@glass@PU. This strategy enables the transformation of rigid perovskite quantum dot glass into flexible luminescent film materials and further improves the photoluminescence quantum yield (PLQY) from 50.5% to 70.2%. The flexible film has good tensile properties, and its length can be strained 5 times as long as the original length. Finally, a white LED was encapsulated by combining CsPbBr3@glass@PU film and red phosphor K2SiF6:Mn4+ with a blue LED chip. The good performance of the obtained CsPbBr3@glass@PU film indicates that it has potential application in flexible liquid crystal displays (LCDs) as a backlight source.

Hydrophobic Modification of Inorganic Perovskite Quantum Dots and LED Applications: Recommending a Comprehensive Chemistry Experiment for Undergraduates

Hydrophobic Modification of Inorganic Perovskite Quantum Dots and LED Applications: Recommending a Comprehensive Chemistry Experiment for Undergraduates

High-performance warm white LED based on thermally stable all inorganic perovskite quantum dots

All inorganic CsPbBr₃ quantum dots (QDs) are regarded as excellent candidates for next-generation emitters due to their high photoluminescence quantum yield (PLQY) and defect tolerance. However, the poor stability and degraded luminescent performance may impede their further commercialization because of the separation of conventional ligands from the QDs surfaces. Recently, Zang replaced the regular oleic acid with 2-hexyl-decanoic acid (DA), which possesses higher binding energy on the QDs surfaces, to act as ligands of QDs, exhibiting PLQY of 96% and excellent stabilities against ethanol and water. WLEDs with DA-modified CsPbBr₃ QDs achieved improved thermal stability, a color rendering index of 93, a power efficiency of 64.8 lm/W and a properly correlated color temperature value of 3018 K, implying their prominent applications in solid-state lighting and displays.

All-Inorganic Perovskite Quantum Dot-Based Blue Light-Emitting Diodes: Recent Advances and Strategies.

Light-emitting diodes (LEDs) based on all-inorganic lead halide perovskite quantum dots (PQDs) have undergone rapid development especially in the past five years, and external quantum efficiencies (EQEs) of the corresponding green- and red-emitting devices have exceeded 23%. However, the blue-emitting devices are facing greater challenges than their counterparts, and their poor luminous efficiency has hindered the display application of PQD-based LEDs (PeQLEDs). This review focuses on the key challenges of blue-emitting PeQLEDs including low EQEs, short operating lifetime, and spectral instability, and discusses the essential mechanism by referring to the latest research. We then systematically summarize the development of preparation methods of blue emission PQDs, as well as the current strategies on alleviating the poor device performance involved in composition engineering, ligand engineering, surface/interface engineering, and device structural engineering. Ultimately, suggestions and outlooks are proposed around the major challenges and future research direction of blue PeQLEDs.

Low‐Power‐Consumption, Reversible 3D Optical Storage Based on Selectively Laser‐Induced Photoluminescence Degradation in CsPbBr3 Quantum Dots Doped Glass

AbstractIn recent years, inorganic lead halide perovskite quantum dots have been used in various optoelectronic fields for their excellent luminescence properties, such as narrow emission bands, ultra‐wide tunable emission wavelength, and high quantum efficiency. In this paper, different from luminescence optimization in most research, luminescence degradation of perovskite quantum dots is addressed by femtosecond laser irradiation and successfully used for three‐dimensional data storage in CsPbBr3 quantum dots doped glass. Photoluminescence (PL) degradation can be finely modulated by adjusting the laser parameters. PL degradation mechanism, investigated by optical spectroscopy and morphology characterization, is attributed to laser‐induced decomposition, recrystallization, and defection of CsPbBr3 quantum dots. Laser‐induced PL degradation and the followed PL recovery by heat treatment are repeated for several cycles, showing good reversibility. Multilayer PL degradation patterns are written into the glass and read out without crosstalk, indicating high‐reliability 3D optical storage characteristics. Amazingly, PL degradation can be induced by just a low‐energy single laser pulse with estimated subpicosecond writing time per bit, demonstrating its potential in high‐speed, low‐power consumption 3D optical storage.

Ultrathin, Transparent, and High Density Perovskite Scintillator Film for High Resolution X-Ray Microscopic Imaging.

Inorganic perovskite quantum dots CsPbX3 (X = Cl, Br, and I) has recently received extensive attention as a new promising class of X‐ray scintillators. However, relatively low light yield (LY) of CsPbX3 and strong optical scattering of the thick opaque scintillator film restrict their practical applications for high‐resolution X‐ray microscopic imaging. Here, the Ce3+ ion doped CsPbBr3 nanocrystals (NCs) with enhanced LY and stability are obtained and then the ultrathin (30 µm) and transparent scintillator films with high density are prepared by a suction filtration method. The small amount Ce3+ dopant greatly enhances the LY of CsPbBr3 NCs (about 33 000 photons per MeV), which is much higher than that of bare CsPbBr3 NCs. Moreover, the scintillator films made by these NCs with high density realize a high spatial resolution of 862 nm thanks to its thin and transparent feature, which is so far a record resolution for perovskite scintillator‐based X‐ray microscopic imaging. This strategy not only provides a simple way to increase the resolution down to nanoscale but also extends the application of as‐prepared CsPbBr3 scintillator for high resolution X‐ray microscopic imaging.

Enhanced piezoelectric and photocatalytic performance of flexible energy harvester based on CsZn0.75Pb0.25I3/CNC–PVDF composite nanofibers

Synthesizing the lead toxicity reduced inorganic perovskite quantum dots (IPQDs) using eco-friendly cellulose nanocrystals (CNC) ligands and mixed with the ferroelectric polymer (polyvinylidene fluoride (PVDF)) for the piezoelectric and photo induced pyrocatalytic applications. IPQDs incorporated PVDF nanofiber render excellent piezoelectricity and intriguingly benefitted with pyro catalytic behavior which becomes the potential of new reusable and toxic-free pyrocatalysts for organic pollution treatments. • Crystallinity of PVDF enhanced with CsPb 0.25 Zn 0.75 I 3 /CNC quantum dot fillers. • Highly flexible and sensitive PPNG device applied to track the human body motions. • The PPNG produces a maximum power density of 29 μm cm −3 with 8 MΩ resistive load. • Photo pyrocatalytic activity of PPNG is investigated by oxidizing Rhodamine dye. The development of high-performance, bio-energy-harvesting and green energy production materials remains a major objective. Perovskite quantum dots have been recently emerging as a potentially relevant material because of their outstanding optoelectronic properties; however, some issues regarding instability and environmental impact remains as stumbling blocks. This research presents a promising and facile method for incorporating lead toxicity reduced inorganic perovskite quantum dots (IPQDs; CsPb 0.25 Zn 0.75 I 3 ) with eco-friendly cellulose nanocrystal (CNC) ligands into polyvinylidene fluoride (PVDF) electrospun nanofibers (PPNG) forming potential piezoelectric and pyroelectric applications. Applying distinct pressures through finger tapping, air pressure, hand bending, fist beating, and foot striking generates intriguing self-powered energy harvesting sensory performances. PPNG produces stable and sensitive signals with highest open-circuit voltage of 20.3 V, short circuit current of 1.2 μA cm −2 , and power density of 29.0 μW cm −3 . Furthermore, the material was found to be successful in pyrocatalytic decay of Rhodamine-B dye; the maximum dye decay was 91% and it exhibits five reusable cycles with ultra-low lead leakages (<1 ppm) because of the photo thermal property of the IPQDs, and excellent stability offered by dual encapsulation. The wearable and durable performances exhibited by the PPNGs can potentially bring limelight in the fabrication of scalable wearable optoelectronic device.

Unraveling the Effect of Surface Ligands on the Auger Process in an Inorganic Perovskite Quantum-Dot System.

This work systematically scrutinizes the role of surface-ligand modification in affecting the Auger process in a porotype perovskite system of CsPbBr3-octanoic acid (OcA) and CsPbBr3-oleic acid (OA) quantum dots (QDs), by means of steady-state/time-resolved/temperature-dependent photoluminescence spectroscopy and ultrafast transient absorption spectroscopy. The difference in the ligand chain length (i.e., C8 and C18 alkyl chains for OcA and OA, respectively) is found to significantly affect Auger recombination and hot-carrier cooling processes. More importantly, we provide fresh insight into the involved carrier dynamics; i.e., the modification of CsPbBr3 QDs with short-chain (long-chain) ligand leads to the formation of trapped (free) carriers, which causes a pronounced difference in the ability to suppress the detrimental Auger process. In addition, a careful analysis of spectral evolution reveals that the Auger suppression is related to the carrier population of a certain transition state. The valuable mechanistic information gleaned from the exciton/carrier dynamics perspective would assist in surface engineering through a facile ligand-modification strategy toward rational design and optimization of QD-based photoelectrochemical applications.

In Situ Synthesis of Monodispersed CsPbBr3/PGMA‐EDMA Microspheres with High Stability for White Light‐Emitting Diodes

AbstractRecently, perovskite quantum dots (PQDs) have attracted significant attention owing to their excellent optoelectronic properties in efficient white light‐emitting diodes (WLEDs). However, their poor stability for UV irradiation and high temperature hinders their practical applications. In this study, CsPbBr3 inorganic perovskite quantum dots (CPB QDs) are in situ grown into the channels of PGMA‐EDMA microspheres to improve their UV irradiation and thermal stability. Moreover, It is found that the pore structure of the PGMA‐EDMA microspheres can effectively block the aggregation between the CPB QDs, which effectively reduces the anion exchange and self‐absorption of fluorescence. Finally, A WLED is fabricated with the CPB/PGMA‐EDMA microspheres and the red‐emitting BaGe4O9:Eu3+ phosphor as color converters; The Commission Internationale de I'Eclairage color coordinates of the fabricated WLED is (0.33, 0.34), which is close to the standard white emission coordinate (0.33, 0.33). The luminous efficiency of as‐prepared WLED is 34.9 lm W−1 with a color render index (CRI) of 74.6, demonstrating that the CPB/PGMA‐EDMA microspheres are potential for application in lighting and display technologies.

Polychromatic tunable luminescence of Eu3+ doped CsPbBr3 quantum dot glass ceramic induced by mechanical crystallization

Nowadays, inorganic perovskite quantum dots (QDs) glass has become a hot topic in the field of new optical materials. In this work, the Eu3+ doped CsPbBr3 QDs phosphate glass has been successfully prepared. Different from the traditional heat treatment method, the CsPbBr3 QDs were prepared by mechanical crystallization. When the QDs glass was ground at different times, due to the synergistic effect of red emission (Eu3+) and green emission (CsPbBr3 QDs), the prepared QDs glass can produce the red-yellow-green polychromatic luminescence phenomenon. Benefit from the dual-emission centers of CsPbBr3 QDs and Eu3+ which do not interfere with each other, the relative sensitivity of the temperature sensing is up to 2.11% K-1, proving that the prepared Eu3+ doped QDs glass has practical application in the field of temperature sensing. The glass material obtained in this way not only has tunability and favorable sensitivity but also provides an effective way for the preparation of QDs.

Synergistic Effects of Multifunctional Lanthanides Doped CsPbBrCl2 Quantum Dots for Efficient and Stable MAPbI3 Perovskite Solar Cells

AbstractThe passivation effect of inorganic perovskite quantum dots (PQDs) is a promising method to attain outstanding performance in perovskite solar cells (PSCs), which has ignited widespread interest recently. Lanthanides (Ln) doped PQDs demonstrate unique properties, but nevertheless, are not explored in PSCs. In this work, four kinds of Ln3+ doped CsPbBrCl2 PQDs (Ln3+ = Yb3+, Ce3+, Eu3+, Sm3+) are firstly introduced into PSCs, which displays the synergistic effect of composition engineering and defect engineering. The results indicate that the introduction of CsPbBrCl2: Ln3+ can not only improve the crystallinity and passivate the intrinsic and surface defects of the MAPbI3 layer through ion and ligand passivation, but also form a stronger LnI bond than PbI, adjust work function (WF), and optimize band alignments. CsPbBrCl2:Sm3+ PQDs possess the best performance and exhibit remarkable promotions of open‐circuit voltage (Voc) from 1.13 to 1.20 V and power conversion efficiency from 18.54% to 22.52%. The humid‐resist, thermal‐resist abilities, and the long‐term stability of PSCs are energetically improved due to enhanced structure stability by Sm3+ doping and the hydrophobic characteristic. The strategy of Ln3+ doped PQDs applied to PSCs provide an approach to achieve high‐performance PSCs.

Highly luminescent MAPbI3 perovskite quantum dots with a simple purification process via ultrasound-assisted bead milling.

Organic–inorganic hybrid lead halide perovskite quantum dots (QDs) have various excellent optical properties, and they have drastically enhanced the field of light-emitting diode (LED) research. However, red-emissive CH3NH3 (MA) PbI3 QDs have worse optical properties compared with those of green-emissive MAPbBr3 QDs due to their instability under high-moisture and high-temperature conditions. Therefore, it is quite difficult to prepare MAPbI3 QDs with good optical properties via bottom-up methods using conditions involving high temperature and high-solubility solvents. On the other hand, top-down methods for preparing MAPbI3 QDs under an air atmosphere have attracted attention; however, there are issues, such as PL emission with a wide FWHM being obtained due to the wide particle-size distribution. In this research, red-emissive MAPbI3 QDs were prepared via an ultrasound-assisted bead milling (UBM) method, and the MAPbI3 QDs were purified using various carboxylate esters. As a result, we solved the issue of the wide particle-size distribution unique to top-down methods via purifying the MAPbI3 QDs, and they achieved the following excellent optical properties: a FWHM of 44 to 48 nm and a PLQY of over 60%. Notably, a fabricated LED device with MAPbI3 QDs purified using methyl acetate showed a PL peak at 738 nm and a FWHM of 49 nm, resulting in an excellent EQE value of 3.2%.

Drop-casting CsPbBr3 perovskite quantum dots as down-shifting layer enhancing the ultraviolet response of silicon avalanche photodiode

Since the absorption zone of ultraviolet (UV) photons with high energy is limited to a few tens of nm on the surface, the high defect density caused by the processes, such as ion implantation, leads to a weak response of the silicon avalanche photodiode (APD) in the ultraviolet band. In this work, the integration of the inorganic perovskite quantum dots (QDs) film by drop-casting as the down-shifting layer is reported for enhancing the UV response of Si APD. The light generated current increases 100% under the 365 nm light emitting diode. The response of the Si APD is improved in the entire ultraviolet band. In particular, the responsivity of APD is increased by 78% at 340 nm with an exceedingly EQE of 92%. In summary, the perovskite QDs film as a down-shifting layer provides an effective and low-cost method to improve the UV response of Si APD.

One-Step Prepared Water-Resistant Organic-Inorganic-Hybrid Perovskite Quantum Dots with Zn-Oxygen Vacancies for Attempts at Nitrogen Fixation.

Applying organic-inorganic hybrid perovskite quantum dots (PQDs) to photocatalytic nitrogen fixation is hindered long-term by the inherent instability in water and tedious preparations. Here, to realize PQD-catalyzed photocatalytic N2 reduction reaction (NRR), water-resistant PQDs are simply prepared through one-step electrospray synthesis in microseconds. During the fast electrospray, PQDs of Zn/PbO-doped methylammonium lead bromide (Zn/PbO/PC-Zn/MAPbBr3 , MA: CH3 NH3 ) are prepared and part-encapsulated by polycarbonate. The synthesis maintains good water resistance, whose restriction on charge transport is overcome skillfully. Simultaneously, substitution of Zn with Pb on water-resistant surface is also achieved, which fabricates new Zn-oxygen vacancies (Zn-OVs) with Zn/PbO-Zn/MAPbBr3 type I heterojunction. This facilitates efficient electron transfer from internal heterojunction interface of Zn/MAPbBr3 PQDs to the surface of Zn/PbO. Demonstrated by theoretical calculations, Zn-OVs promote chemisorption and polarization of N2 . In addition, s-electrons in exposed Zn become active due to changes of electron filling of Zn orbitals under OVs' co-doping. Thus, photocatalytic N2 reduction reaction catalyzed by organic-inorganic hybrid PQDs is first achieved in aqueous phase without sacrificial agents being added. This initiates possibilities for photocatalytic applications of organic-inorganic hybrid PQDs in aqueous phase.

On-and-off feedback control with hysteresis algorithm for automatic flow chemistry synthesis of the desired MAPbBrXI3-X quantum dot

Recent advances in the development of hybrid organic–inorganic halide perovskite quantum dots (HP-QDs) have proven their versatility and potential applications in photovoltaics and light sources through compositional tuning. However, the compositional complexity for mixed-cation and/or mixed-halide HP-QDs would require repetitive optimization processes to obtain the desired perovskite crystals via traditional batch-scale chemistry, causing prolonged time, labor, and cost. To address this issue, we herein report a dynamic flow chemistry synthetic system operated with the on-and-off feedback control with hysteresis algorithm to produce methylammonium lead trihalide perovskite quantum dots (MAPbBrXI3-X QDs with 0 ≤ X ≤ 3), automatically showing a target emission wavelength. We set up the target photoluminescent (PL) emission wavelength of the MAPbBrXI3-X QDs and started with an arbitrary flow rate of the bromide and iodide precursor solution. The PL emission wavelength of the synthesized perovskites was in-situ monitored in the flow cell equipped with a miniaturized optical detector. By comparing the measured wavelength with the target one, the controlling algorithm recalculated to adjust the flow rates of the bromide and iodide precursor solution accordingly. Then, the PL emission wavelength of the newly synthesized MAPbBrXI3-X QDs was detected again in real-time, and the iterative feedback control process was repeated until the observed wavelength was matched with the user-defined emission target. Thus, the desired MAPbBrXI3-X QDs could be obtained eventually through the feedback control in an automatic manner, suggesting an advanced flow chemistry synthetic platform to produce on-demanded nanomaterials with high efficiency.

Facile room-temperature synthesis of highly air‐stable and moisture-resistant CsPbX3/SiO2 nanocomposites for tunable white light-emitting diodes

All inorganic perovskite quantum dots (PQDs) and perovskite CsPbX3/SiO2 nanocomposites (PNCs) have shown their potentials for optical and lighting applications. We demonstrate a one-step approach to synthesize PQDs and PNCs more simply and effectively at room temperature in the open air. The resulting PNCs can show a narrow emission in the PL spectra and high stability under ambient conditions. In particular, both green CsPbBr3/SiO2 and red CsPbI3-xBrx/SiO2 PNCs can be obtained by employing this easy and low-cost method. Even, the SiO2 protection can also effectively prevent the halide exchange reaction between green and red PNCs, meaning the capability for white light applications. The resulting white light-emitting diodes (WLEDs) based on the green and red PNCs coated on the blue LED have a white Commission Internationale del’ Enclairage (CIE) coordinates of (0.375, 0.362) and a low correlated color temperature (CCT) of 4054 K.

Rapid large-scale synthesis of highly emissive solid-state metal halide perovskite quantum dots across the full visible spectrum

The practical applications of solid-state inorganic CsPbX3 perovskite quantum dots (PQDs) have been restricted by their poor stability. Herein, we report an efficient large-scale synthesis of solid-state CsPbX3 PQDs across the full visible spectra using 3-Aminopropyltrimethoxysilane as ligands at room temperature in open air. The obtained green CsPbBr3 solids display outstanding optical performance with high color purity of 90% and photoluminescence quantum yield of 69.2%. Thanks to the protection of silica coating, the solid-state product shows much higher thermal stability, photo stability and long-term stability than that of naked CsPbBr3 QDs. The blue CsPb(Br/Cl)3 and yellow or red CsPb(Br/I)3 PQDs solids can be simply obtained via using alkali metal halide aqueous solution as additives. The white LED fabricated by combining the obtained green CsPbBr3 QDs solid powders and commercial red K2SiF6: Mn4+ phosphor with a blue LED chip displays high luminous efficiency of 70.47 lm/W and the color gamut can cover over 129.4% of the National Television System Committee standard.