All-inorganic Lead Halide Perovskite Quantum Research Articles

Comprehensive Neurotoxicity of Lead Halide Perovskite Nanocrystals in Nematode Caenorhabditis elegans.

To date, all-inorganic lead halide perovskite quantum dots have emerged as promising materials for photonic, optoelectronic devices, and biological applications, especially in solar cells, raising numerous concerns about their biosafety. Most of the studies related to the toxicity of perovskite quantum dots (PeQDs) have focused on the potential risks of hybrid perovskites by using zebrafish or human cells. So far, the neurotoxic effects and fundamental mechanisms of PeQDs remain unknown. Herein, a comprehensive methodology is designed to investigate the neurotoxicity of PeQDs by using Caenorhabditis elegans as a model organism. The results show that the accumulation of PeQDs mainly focuses on the alimentary system and head region. Acute exposure to PeQDs results in a decrease in locomotor behaviors and pharyngeal pumping, whereas chronic exposure to PeQDs causes brood decline and shortens lifespan. In addition, some abnormal issues occur in the uterus during reproduction assays, such as vulva protrusion, impaired eggs left in the vulva, and egg hatching inside the mother. Excessive reactive oxygen species formation is also observed. The neurotoxicity of PeQDs is explained by gene expression. This study provides a complete insight into the neurotoxicity of PeQD and encourages the development of novel nontoxic PeQDs.

Hybrid Interfacial Engineering: An Enabling Strategy for Highly Sensitive and Stable Perovskite Quantum Dots/Organic Heterojunction Phototransistors

All-inorganic lead halide perovskite quantum dots (PQD) have attracted tremendous research interest in the field of phototransistors due to their excellent optoelectronic properties. However, the inefficient charge transport/extraction and high trap-state density of the assembled PQD films seriously limit the photoresponsivity of PQD-based phototransistors. Herein, we demonstrate that these limits can be overcome by adopting a novel device architecture composed of a polar-polymer capping layer on a PQD/organic semiconductor (OSC) heterojunction. The polar polymer film plays the role of both electron trapping and encapsulation, whereas OSC provides the fast transport tracks for charges and PQD serves as the photoactive materials. Owing to the balanced dynamic processes of photogenerated charges, highly sensitive photodetection is achieved, as demonstrated by the peak photosensitivity of 1.5 × 104, a photoresponsivity of 2.1 × 104 A/W, a detectivity of 1 × 1015 Jones, and a high gain of 6.4 × 104 under weak incident light of 3 μW/cm2. Additionally, the phototransistors exhibit superior stability and reproducibility with negligible changes in the output current both in darkness and under illumination after storing for 4 months. The results demonstrate the promising potentials of the polar polymer/PQD/OSC heterojunction for high-performance photodetectors, and the mechanism and strategy described here can be applied to other kinds of quantum dots-based optoelectronic devices.

Self-powered photodetectors based on CsPbBr3 quantum dots/organic semiconductors/SnO2 heterojunction for weak light detection

All-inorganic lead halide perovskite quantum dots (QDs) show great potential in the development of photodetectors (PDs) due to their excellent photoelectric properties. However, the photoresponse performance of the pure perovskite QDs-based PDs is usually limited by the poor charge transport efficiency of the perovskite QDs films. Here, high-performance self-powered PDs based on perovskite QDs and organic semiconductor PQT-12 (poly(3,3‴-didodecyl quarterthiophene)) are reported. Even in a self-powered mode, the devices can still show stable photoresponse to light signals and achieve excellent photodetection performance, including a detectivity up to 5.8 × 1012 Jones, and Ilight/Idark ratio up to 105. More importantly, the devices exhibit obvious photoresponse to weak light with intensity as low as 3 nW cm−2. To the best of our knowledge, the weak light detection ability of the device is better than most reported PDs based on perovskite QDs. In addition, the devices can be fabricated into flexible PDs with almost unchanged photocurrent under different bending angles. The overall performances of our devices are excellent among the reported self-powered PDs. This method utilized here provides new guides for developing high-performance self-powered PDs based on perovskite QDs for weak light detection.

Concentration dependence of photoluminescence properties and exciton dynamics in Mn:CsPb(BrCl)3 quantum dots

All-inorganic lead halide perovskite quantum dots (IPQDs) display some intriguing magnetic, electronic, and optical properties by introducing a transition metal Mn element. In this Letter, Mn-doped CsPb(BrCl)3 IPQDs with a cubic structure have been synthesized by the hot injection method. What make us excited is that the photoluminescence properties of a fixed ensemble of Mn-doped CsPb(BrCl)3 IPQDs systematically depend on the varying concentration. This experimental phenomenon can be well explained by the quantitative model based on photon reabsorption. The results combining experiments with theoretical models indicate that the photon reabsorption is of paramount importance in the analysis of the luminescence properties of colloidal quantum dots especially at high concentrations. Further analysis based on time-resolved fluorescence and transient absorption spectroscopy reveals the effect of the solution concentration on the Mn-doped CsPb(BrCl)3 IPQD exciton dynamics. The results suggest that exciton energy transfer can take place both inside and between IPQDs and also can be enhanced by increasing the concentration of a Mn-doped CsPb(BrCl)3 IPQD solution. These results are of great significance to accurately interpret and control the luminescence properties of IPQDs.

Enhancing the stability of perovskite quantum dots CsPbX3 (X=Cl, Br, I) by encapsulation in porous Y2O3 nanoparticles for WLED applications

Recently, all-inorganic lead halide perovskite quantum dots (PQDs) have raised great attention for various outstanding properties. Although it is a promising candidate for white light emitting diodes (WLED) application, stability issue remains a challenge. In this work, by using a one-step strategy, we successfully achieved nano-sized Y2O3 nanoparticle assisted stability enhancement of multiple all-inorganic lead halide perovskite. Photostability and environmental stability tests show that all dispersed composites retain most of the fluorescence properties. A WLED is fabricated based on as-prepared CsPbBrI2/P-Y2O3 composite. The Commission Internationale de I'Eclairage (CIE) color coordinates of the fabricated WLED is (0.34, 0.35), which is close to the standard white emission coordinate (0.33, 0.33). The luminous efficiency of as-prepared WLED is 61 lm/W with a color render index (CRI) of 83, demonstrating that CsPbBrI2/P-Y2O3 is potential for application in lighting and display technologies.

In Situ Spectroelectrochemical Investigation of Perovskite Quantum Dots for Tracking Their Transformation

All-inorganic lead-halide perovskite quantum dots (PQDs) (CsPbX3, where X is Cl, Br, or I) have been used successfully in optoelectronic applications, such as solar cells, light-emitting diodes, photocatalysts, and lasers. These PQDs work under electrochemical bias and/or illumination with charge separation/collection by interacting with the charge-transport medium. In this study, we discuss the spectroelectrochemical characteristics of PQDs to understand the oxidation and reduction processes that occur during photoinduced charge transport or charge injection under electrochemical conditions. We also found that the PQDs underwent irreversible transformation to the precursor state of plumbate complexes under electrochemical conditions. Furthermore,in situspectroelectrochemical analysis demonstrated that hole-mediated electrochemical oxidation of PQDs resulted in their irreversible transformation. Finally, the results presented herein contribute to our understanding of the charge-transfer-mediated process in PQDs and enhance their application potential in optoelectronic devices.

Emission Quenching and Recovery of Illuminated Perovskite Quantum Dots Due to Iodide Ion Migration.

All-inorganic lead halide perovskite quantum dots (PQDs) are well-known to easily lose their luminescence emission under light illumination, which is often attributed to a photoinduced degradation mechanism. Here, we demonstrate that such quenched emission of PQDs can completely recover in the dark at room temperature, which occurs through a spontaneous "self-healing" mechanism. Our findings indicate that the loss of emission under light illumination is not due to the generally accepted photoinduced degradation, as otherwise the complete recovery would not be possible. Instead, we attribute the emission loss and its subsequent recovery to the migration of iodide ions on the PQD surface. Under illumination, the iodide ions migrate out and associate to adjacent lead ions on the PQD surface, leading to halide vacancies, lattice distortions, and fluorescence quenching. During the recovery process, the migrated iodide ions spontaneously migrate back and fill halide vacancies, resulting in fluorescence recovery. The results of this study offer a useful solution on how to improve the emission and photostability of PQDs.

Effective infrared emission of erbium ions doped inorganic lead halide perovskite quantum dots by sensitization of ytterbium ions

Abstract Rare earth ions doped all-inorganic lead halide perovskite quantum dots (PeQDs) have attracted extensive attention due to the rare earth ions doping greatly expanding the optical properties of PeQDs. Here, Er3+ and Yb3+ ions co-doped CsPbCl3 PeQDs are synthesized by the improved hot-injection method. The excitonic emission and near-infrared (NIR) IIb emission of Er3+ ions and quantum-cutting emission of Yb3+ ions were observed in CsPbCl3:Yb3+, Er3+ PeQDs. Interestingly, the NIR IIb emission of Er3+ ions is only obtained in PeQDs through the effective sensitization of Yb3+ ions. The energy transfer efficiency from Yb3+ to Er3+ ions is 23.5%. Furthermore, the optimal photoluminescence quantum yield (PLQY) of a NIR IIb emission for Er3+ ions was got by typical anion exchange reaction, and the value is up to 14.6%. This work provides a new way that further extends the emission wavelength of PeQDs to NIR IIb region, which will broaden the application scope of PeQDs.

Anomalous variable-temperature photoluminescence of CsPbBr3 perovskite quantum dots embedded into an organic solid.

All-inorganic lead halide perovskite quantum dots (PQDs) of CsPbBr3 were synthesized at room temperature via a facile solution-based procedure. The cubic phase structure of the synthesized PQDs was judiciously identified through examining high-resolution transmission electron microscopy (TEM) images, selected area electronic diffraction (SAED) patterns and scanning TEM images of the PQDs. Variable-temperature photoluminescence (PL) spectra of the CsPbBr3 PQDs randomly embedded into a frozen solid of methylbenzene were measured in the temperature range of 5-180 K. It is found that both the linewidth and peak position of the measured PL spectra are abnormally almost temperature independent in the temperature range of interest. Some competing mechanisms, such as a competition between the bandgap blue shift induced by thermal lattice expansion and red shift induced by thermal escaping of localized excitons, and a competition between lineshape broadening by phonon scattering and narrowing by thermal escaping of localized excitons, are proposed to interpret the phenomena. Good agreement between the theoretical fitting and the experimental data leads to a state-of-the-art understanding of the temperature-dependent luminescence of the CsPbBr3 PQDs in a solid matrix.

Improved stability of CsPbBr3 perovskite quantum dots achieved by suppressing interligand proton transfer and applying a polystyrene coating.

All-inorganic lead halide perovskite quantum dots (PQDs) have shown great promise for optoelectronic applications due to their unique optical and electrical properties. However, their poor stability against moisture, UV light or thermal attacks greatly hinders their practical applications. One of the reasons for this instability is the proton transfer between oleic acid (OA) and oleylamine (OLA), which induces serious ligand loss. The idea of this work is to prevent the interligand proton transfer by replacing OLA with cetyl trimethylammonium bromide (CTAB) that cannot be protonated. The synthesized CsPbBr3 PQDs in solution show high photoluminescence quantum yields up to 71% and also exhibit higher stability against acetone than the counterparts synthesized using oleylammonium bromide (OLABr). Subsequently, CsPbBr3 PQDs with a peak wavelength of 515 nm (g-CsPbBr3) synthesized using CTAB are further composited with a polymer of carboxyl-functionalized polystyrene (cPS). The composite shows enhanced thermal and moisture stability. It is demonstrated that this green-emitting composite can produce high color gamut (130%) white light-emitting diodes when combined with the K2SiF6:Mn4+ phosphor and a blue InGaN chip, enabling its use in display backlights.

Bright Tail States in Blue-Emitting Ultrasmall Perovskite Quantum Dots.

All-inorganic lead halide perovskite quantum dots (CsPbBr3 QDs) are attracting significant research interests because of their highly efficient light-emitting performance combined with tunable emission wavelength facilely realized by ion exchange. However, blue emission from perovskite QDs with strong quantum confinement is rarely reported and suffers from lower luminescence efficiency. Here we report blue-emitting ultrasmall (∼3 nm) CsPbBr3 QDs with photoluminescence (PL) quantum yield as high as 68%. Using time-resolved and steady-state PL spectroscopy, we elucidate the mechanism of the highly efficient PL as recombination of excitons localized in radiative band tail states. Through analyzing the spectral-dependent PL lifetime and the PL line shape, we obtain a large band tail width of ∼80 meV and a high density of state of ∼1020 cm-3. The relaxation of photocarriers into the radiative tail states suppresses the capture by nonradiative centers. Our results provide solid evidence for the positive role of band tail states in the optical properties of lead halide perovskites, which can be further tailored for high-performance optoelectronic devices.

High-Performance Inorganic Perovskite Quantum Dot-Organic Semiconductor Hybrid Phototransistors.

All-inorganic lead halide perovskite quantum dots (IHP QDs) have great potentials in photodetectors. However, the photoresponsivity is limited by the low charge transport efficiency of the IHP QD layers. High-performance phototransistors based on IHP QDs hybridized with organic semiconductors (OSCs) are developed. The smooth surface of IHP QD layers ensures ordered packing of the OSC molecules above them. The OSCs significantly improve the transportation of the photoexcited charges, and the gate effect of the transistor structure significantly enhances the photoresponsivity while simultaneously maintaining high Iphoto /Idark ratio. The devices exhibit outstanding optoelectronic properties in terms of photoresponsivity (1.7 × 104 A W-1 ), detectivity (2.0 × 1014 Jones), external quantum efficiency (67000%), Iphoto /Idark ratio (8.1 × 104 ), and stability (100 d in air). The overall performances of our devices are superior to state-of-the-art IHP photodetectors. The strategy utilized here is general and can be easily applied to many other perovskite photodetectors.