All-inorganic CsPbBr3 Perovskite Nanocrystals Research Articles

Ultrastable Dual-Matrix meditated CsPbBr3 composites with enhanced photoluminescence quantum yield and robust circular polarization luminescence

Metal halide perovskite materials have emerged as a focal point of research in the field of circularly polarized luminescence (CPL). However, striking a delicate balance between several crucial parameters, including large luminescence dissymmetry factors (glum), high photoluminescence quantum yields (PLQY), and long-term stability, has proven to be a challenging endeavor. Here, this study presented a pioneering strategy for crafting robust CPL-active inorganic nanomaterial composites utilizing dual-matrix of chiral nematic mesoporous silica (CNMS) and inorganic passivation Cs4PbBr6 layer. The use of free-standing CNMS hard templates provided a confined growth environment for all-inorganic CsPbBr3 perovskite nanocrystals, enabling the conversion of unpolarized light emission into CPL. Through further advancements in the form of effective passivation with inorganic Cs4PbBr6 layer, superior optical performance and stability were achieved in the system. The figure of merit (FM) value for the resultant CsPbBr3/Cs4PbBr6@CNMS composite film reached −7.8 × 10−2, surpassing the performance of current advanced systems. Moreover, the surface passivation, along with the protection offered by the dual-matrix encapsulation, enhanced the resilience of composite film to harsh environments with robust performance. The successful integration of the CPL materials into a circularly polarized light-emitting diode device confirmed their applicability in CPL displays and luminescence applications. This work establishes a reliable and efficient method for the development of high-performance CPL materials and applications.

All-Inorganic CsPbBr3 Perovskite Nanocrystals Synthesized with Olive Oil and Oleylamine at Room Temperature.

Room temperature (RT) synthesis of the ternary cesium lead bromide CsPbBr3 quantum dots with oleic acid and oleylamine ligands was developed by Zeng and coworkers in 2016. In their works, the supersaturated recrystallization (SR) was adopted as a processing method without requiring inert gas and high-temperature injection. However, the oleic acid ligand for haloplumbate is known to be relatively unstable. Hence, in this work, we employed the eco-friendly olive oil to replace the oleic acid portion for the SR process at RT. Resultantly, we found that the cube-shaped nanocrystal has a size of ~40-42 nm and an optical bandgap of ~2.3 eV independent of the surface ligands, but the photoluminescence lifetime (τav) and crystal packing are dependent on the ligand species, e.g., τav = 3.228 ns (olive oil and oleylamine; here less ordered) vs. 1.167 ns (oleic acid and oleylamine). Importantly, we explain the SR mechanism from the viewpoint of the classical LaMer model combined with the solvent engineering technique in details.

TiN Electrode for High-Performance CsPbBr₃ Perovskite Nanocrystal-Based Photodetectors

Solution-processed all-inorganic lead halide perovskites are widely utilized to develop photodetectors (PDs) due to their excellent optoelectronic properties. The low-cost titanium nitride (TiN) electrode not only has better corrosion resistance than Ag electrode but also possesses good conductivity comparable to Au electrode, but the utilization of TiN electrode in perovskite PDs has been rarely reported. Here, based on all-inorganic CsPbBr3 perovskite nanocrystals (NCs) synthesized through the supersaturated recrystallization method, a high-performance metal–semiconductor–metal (MSM)-type PD with a photo-to-dark-current ratio (PDCR) above <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{4}$ </tex-math></inline-formula> and a dynamic range (DR) of 164 dB was demonstrated by employing the low-cost TiN electrode. It indicates that the PD with TiN electrode maintains a dark current as low as that of PD with Au electrode, while that with Ag electrode is hundreds of times inferior. It also reflects that the photocurrent of the PD with TiN electrode is quite close to that of the Au electrode counterpart, which exhibits a 161 times improvement with respect to the PD with Ag electrode. Moreover, the TiN electrode PD demonstrates a much better stability relative to the device with Ag electrode. Our work contributes to developing low-cost, high-performance PDs based on solution-processed semiconductors.

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.

High-performance CsPbBr3@Cs4PbBr6/SiO2 nanocrystals via double coating layers for white light emission and visible light communication

Owing to their outstanding optoelectronic properties, all-inorganic CsPbBr3 perovskite nanocrystals (NCs) are regarded as excellent materials for various optoelectronic applications. Unfortunately, their practical applications are limited by poor stability against water, heat, and polar solvents. Here, we propose a facile synthesis strategy for CsPbBr3@Cs4PbBr6 NCs via tetraoctylammonium bromide ligand induction at room temperature. The resulting CsPbBr3@Cs4PbBr6 NCs show a high photoluminescence quantum yield of 94%. In order to prevent Cs4PbBr6 from being converted back to CsPbBr3 NCs when exposed to water, a second coating layer of SiO2 is formed on the surface of the CsPbBr3@Cs4PbBr6 NCs by the facile hydrolysis of tetramethoxysilane. The resulting CsPbBr3@Cs4PbBr6/SiO2 NCs with their double coating structure have outstanding stability against not only a polar solvent (ethanol) but also water and heat. The as-prepared CsPbBr3@Cs4PbBr6/SiO2 NCs serve as green emitters in efficient white light-emitting diodes (WLEDs) with a high color rendering index (CRI) of 91 and a high power efficiency 59.87 lm W−1. Furthermore, the use of these WLEDs in visible light communication (VLC) results in a maximum rate of 44.53 Mbps, suggesting the great potential of the reported methods and materials for solid-state illumination and VLC.

Inorganic Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite Nanocrystals for Enhanced Optoelectronic Performance.

While the layered hybrid Ruddlesden-Popper (RP) halide perovskites have already established themselves as the frontrunners among the candidates in optoelectronics, their all-inorganic counterparts remain least explored in the RP-type perovskite family. Herein, we study and compare the optoelectronic properties of all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) with and without RP planar faults. We find that the RP-CsPbBr3 PNCs possess both higher exciton binding energy and longer exciton lifetimes. The former is ascribed to a quantum confinement effect in the PNCs induced by the RP faults. The latter is attributed to a spatial electron-hole separation across the RP faults. A striking difference is found in the up-conversion photoluminescence response in the two types of CsPbBr3 PNCs. For the first time, all-inorganic RP-CsPbBr3 PNCs are tested in light-emitting devices and shown to significantly outperform the non-RP CsPbBr3 PNCs.

Influence of the rate of radiation energy on the charge-carrier kinetics application of all-inorganic CsPbBr3 perovskite nanocrystals.

In the field of optoelectronics, all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) have gained significant interest on account of their superb processability and ultra-high stability among all the counterparts. In this study, we conducted an in-depth analysis of CsPbBr3 PNCs using joint transient optical spectroscopies (time-resolved photoluminescence and ultrafast transient absorption) in a very comprehensive manner. In order to understand the in-depth analysis of excited-state kinetics, the transient absorption spectroscopy has been performed. The structure of interest of CsPbBr3 PNCs was subjected to the rates of the radiation energy of 0.10 mW (κr/κnr = ∼0.62) and 0.30 mW (κr/κnr = ∼0.64). With the rate of radiation energy 0.30 mW, it was observed that there was a significant increase in hot carrier relaxation together with high radiative recombination, resulting in a decrease in charge trappings. Herein, we demonstrate that the tuning of the rate of radiation energies helps to understand the charge-carrier kinetics of CsPbBr3 PNCs, which would thus improve the manufacturing of efficient photovoltaic devices.

High-speed colour-converting photodetector with all-inorganic CsPbBr3 perovskite nanocrystals for ultraviolet light communication

Optical wireless communication (OWC) using the ultra-broad spectrum of the visible-to-ultraviolet (UV) wavelength region remains a vital field of research for mitigating the saturated bandwidth of radio-frequency (RF) communication. However, the lack of an efficient UV photodetection methodology hinders the development of UV-based communication. The key technological impediment is related to the low UV-photon absorption in existing silicon photodetectors, which offer low-cost and mature platforms. To address this technology gap, we report a hybrid Si-based photodetection scheme by incorporating CsPbBr3 perovskite nanocrystals (NCs) with a high photoluminescence quantum yield (PLQY) and a fast photoluminescence (PL) decay time as a UV-to-visible colour-converting layer for high-speed solar-blind UV communication. The facile formation of drop-cast CsPbBr3 perovskite NCs leads to a high PLQY of up to ~73% and strong absorption in the UV region. With the addition of the NC layer, a nearly threefold improvement in the responsivity and an increase of ~25% in the external quantum efficiency (EQE) of the solar-blind region compared to a commercial silicon-based photodetector were observed. Moreover, time-resolved photoluminescence measurements demonstrated a decay time of 4.5 ns under a 372-nm UV excitation source, thus elucidating the potential of this layer as a fast colour-converting layer. A high data rate of up to 34 Mbps in solar-blind communication was achieved using the hybrid CsPbBr3–silicon photodetection scheme in conjunction with a 278-nm UVC light-emitting diode (LED). These findings demonstrate the feasibility of an integrated high-speed photoreceiver design of a composition-tuneable perovskite-based phosphor and a low-cost silicon-based photodetector for UV communication.

Optical Amplification in Hollow-Core Negative-Curvature Fibers Doped with Perovskite CsPbBr3 Nanocrystals.

We report a hollow-core negative-curvature fiber (HC-NCF) optical signal amplifier fabricated by the filling of the air microchannels of the fiber with all-inorganic CsPbBr3 perovskite nanocrystals (PNCs). The optimum fabrication conditions were found to enhance the optical gain, up to +3 dB in the best device. Experimental results were approximately reproduced by a gain assisted mechanism based on the nonlinear optical properties of the PNCs, indicating that signal regeneration can be achieved under low pump powers, much below the threshold of stimulated emission. The results can pave the road for new functionalities of the HC-NCF with PNCs, such as optical amplification, nonlinear frequency conversion and gas sensors.

High-Detectivity Perovskite Light Detectors Printed in Air from Benign Solvents

Summary Here, we propose a simple and low-temperature approach for the synthesis of methylammonium lead halide perovskite inks based on sub-micrometer-sized particles with tunable band gap. The particles allow the formulation of inks in benign solvents, such as propan-2-ol, and the printing of the photoactive layers of planar photoconductors with scalable, large-area coating techniques under ambient conditions. When surface traps are passivated with [6,6]-phenyl-C61-butyric acid methyl ester fullerene (PCBM), a high photoconductive gain (exceeding 200 in the blue) and reduced noise produce record-high specific detectivities exceeding 7 × 1013 cmHz0.5/W and gain-bandwidth product values of 7.5 × 106 Hz. Given the extreme simplicity of the presented device architecture and the straightforward processing, yielding printable light detectors rivalling established technologies, the present work promises a short-term deployment of printed perovskite detectors in a multitude of opto-electronic applications.

Solvent-Assisted Tuning of the Size and Shape of CsPbBr3 Nanocrystals via Redispersion Process at Ambient Condition.

All-inorganic CsPbBr3 perovskite nanocrystals are emerging as a new class of semiconductors with outstanding optoelectronic properties and great potential for various applications, such as, lasing, photon detection, photovoltaics, etc. This article provides the effect of solvents on the reprecipitation of CsPbBr3 perovskite at room temperature. The results observed for CsPbBr3 perovskite in various antisolvents showed various cubes (nano- to microsized), self-assembly of nanocubes and nanorods. In addition, all of the various sizes (nano to micro) of cubes and self-assembly of nanocubes and shape-controlled nanorods exhibited band gap tuning at the green light region. The corresponding microscopy (field emission scanning electron microscopy and high-resolution transmission electron microscopy) images and photoluminescence quantum yield as well as lifetime decay are presented. To the best of our literature knowledge, this is the first report on various solvent-assisted studies on CsPbBr3 perovskite nanocrystals.

Rod-shaped thiocyanate-induced abnormal band gap broadening in SCN− doped CsPbBr3 perovskite nanocrystals

In this work, the pseudohalide thiocyanate has been demonstrated as a promising alternative to the halide anion to engineer optoelectronic properties of inorganic/organic hybrid perovskites because it exhibits better chemical stability than the halide anion. Previous reports have suggested that the ionic radii and electronegativity of SCN− is close to that of I−; the SCN− doped CH3NH3PbI3 exhibited similar optical properties as pure CH3NH3PbI3. Consequently, it was expected that doping of CsPbBr3 perovskite with SCN− would result in band gap narrowing. Interestingly, the photoluminescent all-inorganic CsPbBr3 perovskite nanocrystals exhibit an abnormal blue shift in optical properties and improvement of the crystallinity when successfully doped by SCN−. Combined experimental and theoretical investigations revealed that doping of the CsPbBr3 perovskite with the rod-like SCN− anion introduced disorder in the crystal lattice, leading to its expansion, and impacted the electronic structure of the perovskite with band gap broadening.

White LED based on CsPbBr3 nanocrystal phosphors via a facile two-step solution synthesis route

All-inorganic CsPbBr3 perovskite nanocrystals with mean size of ∼300 nm were synthesized via a facile two-step solution synthesis route. High-resolution transmission electron microscopy and X-ray diffraction characterizations confirm the as-prepared CsPbBr3 nanoparticles are single-crystals with good crystallinity, although a CsPb2Br5 impure phase also exists in the final product. Power-/temperature-dependent and time-resolved photoluminescence measurements reveal the notable and stable excitonic emission feature of these CsPbBr3 nanocrystals. As a proof-of-concept demonstration, a LED with p-GaN/n-ZnO heterojunction as blue-violet excitation chip and CsPbBr3 nanocrystals as green phosphors, was fabricated and a white electroluminescence was achieved from this perovskite nanocrystals decorated LED.

High-temperature synthesis in nonpolar solvent for CsPbBr3 and CH3NH3PbBr3 perovskite nanocrystals with high-efficient luminescence

We report a method to synthesize both organicinorganic CH3NH3PbBr3 and all-inorganic CsPbBr3 perovskite nanocrystals in nonpolar solvent at high temperature. The cesium oleate and CH3NH3Br (MABr) are prepared and then injected into the nonpolar solvent of octadecene including oleic acid, oleylamine, and lead halide. In the synthesis of organic-inorganic perovskites of CH3NH3PbBr3, the frequently-used polar solvent of dimethylformamide or other polar solvents are not used. The prepared CsPbBr3 nanocrystals are spherical nanoparticles with the diameter of 250 nm. The CH3NH3PbBr3 perovskites are micro- scale hexagonal nanoplatelets. The colloidal perovskites exhibit high-efficient fluorescence and excellent stability.

Au Exchange or Au Deposition: Dual Reaction Pathways in Au-CsPbBr3 Heterostructure Nanoparticles.

We have designed a facile synthetic strategy for the selective deposition of Au metal on all-inorganic CsPbBr3 perovskite nanocrystals that includes the addition of PbBr2 salt along with AuBr3 salt. PbBr2 is necessary because the addition of Au3+ to solutions of CsPbBr3 nanocrystals otherwise results in the exchange of Au3+ ions from solution with Pb2+ cations within the nanocrystal lattice to produce Cs2AuIAuIIIBr6 nanocrystals with a tetragonal crystal structure and a band gap of about 1.6 eV, in addition to Au metal deposition. Including excess Pb2+ ions in solution prevents the exchange reaction. Au metal deposits on the surface of the nanocrystals to produce the Au-CsPbBr3 heterostructure nanoparticles with an Au particle diameter determined by the Au3+ ion concentration. Fluorescence quenching caused by Au deposition monotonically increases with deposition size, but the fluorescence quantum yield (QY) is significantly greater than if any cation exchange has occurred. An optimized synthesis can produce Au-CsPbBr3 nanoparticles with 70% QY and no evidence of cation exchange.

Morphology Evolution and Degradation of CsPbBr3 Nanocrystals under Blue Light-Emitting Diode Illumination.

Under illumination of light-emitting diode (LED) or sunlight, the green color of all-inorganic CsPbBr3 perovskite nanocrystals (CPB-NCs) often quickly changes to yellow, followed by large photoluminescence (PL) loss. To figure out what is happening on CPB-NCs during the color change process, the morphology, structure, and PL evolutions are systematically investigated by varying the influence factors of illumination, moisture, oxygen, and temperature. We find that the yellow color is mainly originated from the large CPB crystals formed in the illumination process. With maximized isolation of oxygen for the sandwiched film or the uncovered film stored in nitrogen, the color change can be dramatically slowed down whether there is water vapor or not. Under dark condition, the PL emissions are not significantly influenced by the varied relative humidity (RH) levels and temperatures up to 60 °C. Under the precondition of oxygen or air, color change and PL loss become more obvious when increasing the illumination power or RH level, and the large-sized cubic CPB crystals are further evolved into the oval-shaped crystals. We confirm that oxygen is the crucial factor to drive the color change, which has the strong synergistic effect with the illumination and moisture for the degradation of the CPB film. Meanwhile, the surface decomposition and the increased charge trap states occurred in the formed large CPB crystals play important roles for the PL loss.