All-inorganic Perovskite Nanocrystals Research Articles

Size Dependence of Ultrafast Electron Transfer from Didodecyl Dimethylammonium Bromide-Modified CsPbBr3 Nanocrystals to Electron Acceptors.

Charge transfer efficiencies in all-inorganic lead halide perovskite nanocrystals (NCs) are crucial for applications in photovoltaics and photocatalysis. Herein, CsPbBr3 NCs with different sizes are synthesized by varying the ligand contents of didodecyl dimethylammonium bromide at room temperature. Adding benzoquinone (BQ) molecules leads to a decrease in the PL intensities and PL decay times in NCs. The electron transfer (ET) efficiency (ηET) increases with NC size in complexes of CsPbBr3 NCs and BQ molecules (NC-BQ complexes), when the same concentration of BQ is maintained, as investigated by transient photobleaching and photoluminescence spectroscopies. Controlling the same number of attached BQ acceptor molecules per NC induces the same ηET in NC-BQ complexes even though with different NC sizes. Our findings provide new insights into ultrafast charge transfer behaviors in perovskite NCs, which is important for designing efficient light energy conversion devices.

Synthesis and performance optimization of CsPbBr3/CdS core/shell lead halide perovskite nanocrystals by an ion exchange method

All-inorganic lead halide perovskite nanocrystals (NCs) have excellent optoelectronic properties and promising applications. Improving the stability of inorganic halide NCs and optimizing their photoluminescence quantum yields (PLQY) has become an urgent task. Constructing core-shell structures is an effective method to improve the environmental stability and PLQY, however, realizing core-shell structured perovskite NCs with good dispersion and multiple perovskites encapsulated within the shell material remains challenging. In this work, CdS shells were grown on the surface of CsPbBr3 NCs by ion-exchange method utilizing perovskite NCs with their ionic properties, and the effectiveness of the surface shell protection is reflected in its enhancement of long-term storage stability, storage stability in water, and thermal stability of NCs. In addition, the PLQY and exciton binding energies of CsPbBr3/CdS NCs are increased. Finally, the NCs were packaged into green emitting LED devices and performed high stability. The results will facilitate the further commercialization of all-inorganic lead halide perovskite materials for optoelectronic devices.

Doping Up the Light: A Review of A/B-Site Doping in Metal Halide Perovskite Nanocrystals for Next-Generation LEDs.

All-inorganic metal halide perovskite nanocrystals (PeNCs) show great potential for the next generation of perovskite light-emitting diodes (PeLEDs). However, trap-assisted recombination negatively impacts the optoelectronic properties of PeNCs and prevents their widespread adoption for commercial exploitation. To mitigate trap-assisted recombination and further enhance the external quantum efficiency of PeLEDs, A/B-site doping has been widely investigated to tune the bandgap of PeNCs. The bandgap of PeNCs is adjustable within a small range (no more than 0.1 eV) by A-site cation doping, resulting in changes in the bond length of Pb-X and the angle of [PbX6]4. Nevertheless, B-site doping of PeNCs has a more significant impact on the bandgap level through modification of surface defect states. In this perspective, we delve into the synthesis of PeNCs with A/B-site doping and their impacts on the structural and optoelectronic properties, as well as their impacts on the performance of subsequent PeLEDs. Furthermore, we explore the A-site and B-site doping mechanisms and the impact of device architecture on doped PeNCs to maximize the performance and stability of PeLEDs. This work presents a comprehensive overview of the studies on A-site and B-site doping in PeNCs and approaches to unlock their full potential in the next generation of LEDs.

Considerable Piezochromism in All-Inorganic Zero-Dimensional Perovskite Nanocrystals via Pressure-Modulated Self-Trapped Exciton Emission.

Piezochromic materials refer to a class of matters that alter their photoluminescence (PL) colors in response to the external stimuli, which exhibit promising smart applications in anti-counterfeiting, optoelectronic memory and pressure-sensing. However, so far, most reported piezochromic materials have been confined to organic materials or hybrid materials containing organic moieties with limited piezochromic range of less than 100 nm in visible region. Here, we achieved an intriguing piezochromism in all-inorganic zero-dimensional (0D) Cs3Cu2Cl5 nanocrystals (NCs) with a considerable piezochromic range of 232 nm because of their unique inorganic rigid structure. The PL energy shifted from the lowest-energy red fluorescence (1.85 eV) to the highest-energy blue fluorescence (2.83 eV), covering almost the entire visible wavelength range. Pressure-modulated self-trapped exciton emission between different energy levels of self-trapped states within Cs3Cu2Cl5 NCs was the main reason for this piezochromism property. Note that the quenched emission, which is over five times more intense than that in the initial state, is retained under ambient conditions upon decompression. This work provides a promising pressure indicating material, particularly used in pressure stability monitoring for equipment working at extreme environments.

Exceptional Stability against Water, UV Light, and Heat for CsPbBr3@Pb-MOF Composites.

All-inorganic lead halide perovskite nanocrystals (NCs) have been widely applied in optoelectronic devices owing to their excellent photoluminescence (PL) properties. However, poor stability upon exposure to water, UV light or heat strongly limits their practical application. Herein, CsPbBr3@Pb-MOF composites with exceptional stability against water, UV light, and heat are synthesized by ultrasonic processing the precursors of lead-based MOF (Pb-MOF), oleylammonium bromide (OAmBr) and cesium oleate (Cs-OA) solutions at room temperature. Pb-MOF can not only provide the lead source for the in situ growth of CsPbBr3 NCs, but also the protective layer of perovskites NCs. The formed CsPbBr3@Pb-MOF composites show a considerable PL quantum yield (PLQY) of 67.8%, and can maintain 90% of the initial PL intensity when immersed in water for 2 months. In addition, the outstanding PL stability against UV light and heat is demonstrated with CsPbBr3 NCs synthesized by the conventional method as a comparison. Finally, a green (light-emitting diode) LED is fabricated using green-emitting CsPbBr3@Pb-MOF composites and exhibits excellent stability without packaging when immersed in water for 30 days. This study provides a practical approach to improve the stability in aqueous phase, which may pave the way for future applications for various optoelectronic devices.

Hysteric Influence of Grain Multiplicity in All-Inorganic Halide Perovskite Nanocrystals

Hysteric Influence of Grain Multiplicity in All-Inorganic Halide Perovskite Nanocrystals

Fabrication of water-resistant fluorescent ink using the near-unity photoluminescence quantum yield of CsPbBr3 doped with NiBr2.

Doping with transition and alkaline earth metal ions into all-inorganic perovskite nanocrystals (NCs) has attracted attention recently for tuning the photoluminescence quantum yield (PLQY). We report on the hot injection synthesis of nickel ion-doped CsPbBr3 NCs with near-unity PLQYs. Nickel ions were successfully incorporated into the octahedral environment of CsPbBr3 NCs, replacing the lead ions. The introduction of nickel ions into CsPbBr3 NCs substantially eliminates intrinsic defects and halide vacancies for improved structural order and near-unity PLQYs. Benefiting from these unique properties, nickel ion-doped CsPbBr3 NCs were dispersed in a polymer to prepare an efficient fluorescent ink. The fluorescent ink shows excellent thermal and water stability under harsh environmental conditions. Moreover, the usefulness of the fluorescent ink for security purposes was demonstrated by designing and recognizing a fluorescent QR code. This study reveals that doped CsPbBr3 NCs can be used to prepare efficient water-resistant fluorescent ink for anti-counterfeiting applications, widening the usefulness of doped all-inorganic perovskite NCs.

Insight into the growth kinetics of CsPbBr3 perovskite nanocrystals using an oil-water droplet fluidic synthesis route

All-inorganic lead halide perovskite nanocrystals (PNCs) have attracted extensive attention in the optoelectronic fields owning to their exceptional photoluminescence characteristics. However, the ultra-fast growth rate of PNCs leads to challenges in controlling their size and optical properties. Here, we report a water–oil droplet fluidic synthesis method that successfully slow down the growth rate of CsPbBr3 PNCs by segregating the cation and anion precursors in the respective phases. Reaction mechanism study revealed a fast nucleation via a nanoplate-intermediate pathway upon HBr diffusion and subsequent slow growth through ripening, leading to a wide range of spectral tunability of the PNCs from 445 nm to 520 nm. The theoretical investigation into growth kinetics showed the combined effect of the ligands and temperature on the growth of the PNCs. This method provides an efficient means for producing high-performance PNCs with tunable size and wavelength while also eliminating the requirement for a Pb-rich reaction environment.

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.

Uniform incorporation of two-dimensional BiOBr into perovskite crystals and films to enhance photoluminescence

The all-inorganic perovskite nanocrystals are promising luminescent materials for optoelectronic devices. However, it is still a challenge to prepare perovskite nanocrystals with high luminescence. Herein, a synthesis method was developed for the uniform incorporation of ultra-thin BiOBr nanosheets into perovskite crystals at both body-embedding and surface-passivating positions. The micron-scale green-emitting phosphors composed of Cs4PbBr6 nanocrystals and BiOBr nanosheets are prepared. The crystal structure of Cs4PbBr6 nanocrystals can remain almost unchanged although prepared from different PbBr2 concentrations. The luminescence mechanism of Cs4PbBr6 is discussed. The Cs4PbBr6@BiOBr submicron phosphors can be dispersed in DMSO solvent without disintegration and dissolution, which are used as seeds of the CsPbBr3 film growth. The CsPbBr3 films with Cs4PbBr6@BiOBr doped exhibit pure optical characteristics of CsPbBr3, indicating that Cs4PbBr6 is converted to CsPbBr3 during the film preparation process. Furthermore, these Cs4PbBr6@BiOBr phosphors are mixed with CaAlSiN3: Eu red-emitting commercial phosphors to make white LEDs (WLEDs). Overall, this study provides a revealing insight into a kind of composite material constructed with halide perovskite and bismuth halide oxide.

Water-stable perovskite-silica nanocomposites for encoded microbeads construction and multiplexed detection

All-inorganic lead halide perovskite nanocrystals exhibiting bright luminescence have great potential as fluorescence elements for optical encoding. However, their limited stability in water hinders the application in biosensing. In this study, novel optical encoded microbeads based on CsPbX3 (X = Cl, Br) nanocrystals are developed and applied in bead-based suspension arrays for the first time. Through the in-situ crystallization of CsPbX3 nanocrystals within mesoporous silica nano-templates (MSNs), accompanied by mesopores collapse after sintering, CsPbX3@MSNs (X3M) nanocomposites with uniform morphology and stable fluorescence intensity in aqueous solutions for up to 50 days are obtained. By assembling X3M with microspheres to form a host–guest structure, an optical encoding microbead (MX3M) library is established by varying the X3M ratio, halide composition, and the size of host microspheres, which can be easily decoded under multi-channel flow cytometer. As a result, MX3M exhibits outstanding capacity for specific target capture and negligible nonspecific absorption performance in the multiplex nucleic acid detection of respiratory viruses, with a low limit of detection (10 copies/rxn). This result highlights the tremendous potential of MX3M encoded microbeads constructed based on CsPbX3 nanocrystals for multiplexed bioassays.

Compound doping enables efficient CsPbBr3 nanocrystal light emitting diodes

All-inorganic cesium-based perovskite nanocrystals (PeNCs) attract much attentions in displays due to their facile synthesis protocol and superior luminous performance, while material instability hinders their practical applications. Herein, by inducing a multi-functional dopant, i.e., SrBr2, into the perovskite precursor solution, the as-formed SrBr2-doped CsPbBr3 NCs possess purer phases, suppressed defects and hydrophobic surfaces, which leads to a high photoluminescence quantum yield of ∼90 %, as well as much improved moisture stability. Benefiting from dopant passivation and improved luminescence properties, the doped CsPbBr3 light emitting diodes show five times and two times of current efficiency and external quantum efficiency improvements, respectively, in comparison to their undoped counterparts.

Enhanced luminescence stability of high-entropy dual-phase Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5 perovskite nanocrystals coated with SiO2 and EVA

All-inorganic halide perovskite nanocrystals (NCs) have attracted much attention in many fields. However, the poor stability of NCs and the toxicity of Pb have greatly hindered their practical applications. Reducing the proportion of Pb with the concept of high-entropy and coating NCs with an outer layer have been regarded as effective strategies to solve the problems. Herein, We have successfully synthesized the all-inorganic high-entropy dual-phase Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5(Cs‘B’Br3/Cs‘B’2Br5) perovskite NCs with good luminescence properties by a high-energy ball milling method; On the basis of which, Cs‘B’Br3/Cs‘B2’Br5 NCs are coated with SiO2 and EVA resin. Due to the amorphous SiO2 protection, the Cs‘B’Br3/Cs‘B2’Br5@SiO2 NCs maintained 93% of their emission intensity after 90 days compared to their uncoated counterparts. The PL intensity of Cs‘B’Br3/Cs‘B2’Br5 NCs /EVA was significantly enhanced by a factor of 4.7 for compared to the uncoated NCs. In addition, the PL emission intensity of the Cs‘B’Br3/Cs‘B2’Br5 NCs /EVA remained 93.7% after 90 days, and the emission peak intensity remained approximately 63% after 8 h of placement in an enclosed environment at 80% humidity through the dense polymer chains and the hydrophobic nature of the film. Finally, the film could expand its application prospects in the field of flexible device.

Bright Green-Emitting All-Inorganic Terbium Halide Double Perovskite Nanocrystals for Low-Dose X-ray Imaging.

Inorganic halide double perovskite (DP) nanocrystals (NCs) have attracted great attention because of their nontoxicity, mild reaction conditions, good stability, and excellent optical and optoelectronic properties. Herein, we prepare the inorganic terbium halide DP Cs2BTbCl6 (B = Na or Ag) NCs with bright green photoluminescence (PL) emission. The Na-Tb-based DP NCs exhibit better PL properties compared with the Ag-Tb-based DP NCs, which is due to Cs2NaTbCl6 NCs having a more localized charge carrier distribution on the [TbCl6]3- octahedron. The incorporation of Sb3+ dopant in Cs2NaTbCl6 NCs can construct a more efficient energy transfer process, resulting in a doubling of PL efficiency. Furthermore, Cs2NaTbCl6: Sb3+ NCs possess excellent X-ray scintillating performance with a low-dose detection limit of 140 nGyair/s, which is nearly 5 times more sensitive than the undoped NCs. The optimized NCs show great application prospects in X-ray imaging. This work helps deepen the understanding of the luminescence mechanism, excited state dynamics, and scintillation property in Tb-based DP NCs.

One-step synthesis of all-inorganic high-entropy dual-phase Cs‘B’Br3/Cs‘B’2Br5 perovskite nanocrystals by high-energy ball milling

All-inorganic lead halide perovskite nanocrystals (NCs) have attracted considerable attention in field of optoelectronics due to their excellent properties such as high PLQY, tunable emission spectra in visible light region, and narrow emission peaks. However, problems existing in the research of all-inorganic lead halide perovskite materials are high lead content, low stability, and complex synthesis processes. Those problems need to be solved urgently. Therefore, dual-phase Cs‘B’Br3/Cs‘B’2Br5 perovskite material (Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)Br3/Cs(Pb1/5Mn1/5Ni1/5Zn1/5Cd1/5)2Br5) was synthesized by doping the B-site of CsPbBr3 and CsPb2Br5 using high-energy ball milling in this thesis. This dual-phase perovskite material has maximum absorption edge of 540 nm, a band gap width of 2.22 eV, the maximum emission peak at 600 nm with FWHM of 72 nm, PLQY of 24.50%, and an average fluorescence lifetime of 227.87 μs. After 21 days at room temperature, luminescent intensity of NCs increased to 156%, and still retained 109% at 120 days. After treatment at 150 °C, luminescent intensity decreased to 47%. Results show that this high-entropy dual-phase perovskite has great stability in different temperature. This proves that synthesis of high-entropy dual-phase halide perovskite by high-energy ball milling is feasible, and has great significance in solving poor stability and high lead content of all-inorganic lead halide perovskite in the future.

Synergistic Halide- and Ligand-Exchanges of All-Inorganic Perovskite Nanocrystals for Near-Unity and Spectrally Stable Red Emission.

All-inorganic perovskite nanocrystals (NCs) of CsPbX3 (X = Cl, Br, I) are promising for displays due to wide color gamut, narrow emission bandwidth, and high photoluminescence quantum yield (PLQY). However, pure red perovskite NCs prepared by mixing halide ions often result in defects and spectral instabilities. We demonstrate a method to prepare stable pure red emission and high-PLQY-mixed-halide perovskite NCs through simultaneous halide-exchange and ligand-exchange. CsPbBr3 NCs with surface organic ligands are first synthesized using the ligand-assisted reprecipitation (LARP) method, and then ZnI2 is introduced for anion exchange to transform CsPbBr3 to CsPbBrxI3-x NCs. ZnI2 not only provides iodine ions but also acts as an inorganic ligand to passivate surface defects and prevent ion migration, suppressing non-radiative losses and halide segregation. The luminescence properties of CsPbBrxI3-x NCs depend on the ZnI2 content. By regulating the ZnI2 exchange process, red CsPbBrxI3-x NCs with organic/inorganic hybrid ligands achieve near-unity PLQY with a stable emission peak at 640 nm. The CsPbBrxI3-x NCs can be combined with green CsPbBr3 NCs to construct white light-emitting diodes with high-color gamut. Our work presents a facile ion exchange strategy for preparing spectrally stable mixed-halide perovskite NCs with high PLQY, approaching the efficiency limit for display or lighting applications.

Preparation and fluorescence properties of SiO2-coated CsPbBrI2 perovskite nanocrystals

All-inorganic perovskite nanocrystals CsPbX3 (X=Cl, Br, I) have garnered significant interest due to their promising applications and have become a leading research subject in the field of optoelectronics. The weak stability of CsPbBrI2 perovskite nanocrystals has hindered their development, however, silica coating can effectively solve this problem. The (3-aminopropyl) triethoxysilane was used as a raw material for silica synthesis to form core-shell structured CsPbBrI2@SiO2 perovskite nanocrystals to obtain enhanced optoelectronic properties. This article reveals the narrow absorption and emission peaks, small half-height widths, 14.6 ns fluorescence lifetimes, and 106.2 meV exciton binding energies of CsPbBrI2@SiO2 perovskite nanocrystals. The results show that the core-shell structured CsPbBrI2@SiO2 perovskite nanocrystals prepared by this method have excellent fluorescence spectral properties and hold significant promise for future applications in optoelectronic devices.

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.

Synthesis of All-Inorganic Halide Perovskite Nanocrystals for Potential Photoelectric Catalysis Applications

Compared with conventional semiconductors, halide perovskite nanocrystals (NCs) have a unique crystal structure and outstanding optoelectronic properties, offering wide potential for applications in optoelectronic devices such as solar cells, photodetectors, light-emitting diodes, lasers, and displays. Rational technological design is providing vital support for the development of perovskite optoelectronics. Herein, monodisperse all-inorganic halide perovskite nanocrystals with consistent morphology and cubic crystal phase were synthesized employing a modified one-pot hot injection method to independently modulate the stoichiometric ratios of three precursors involving cesium salt, lead source, and halide. In combination with an anion exchange reaction, mixing two kinds of perovskite NCs with different halogens enables a transition from violet emission to green and finally to red emission over the entire visible region. Additionally, optical and electrochemical tests suggested that the as-synthesized halide perovskite NCs are promising for photoelectric catalysis applications.

High-Performance Optoelectronic Gas Sensing Based on All-Inorganic Mixed-Halide Perovskite Nanocrystals with Halide Engineering.

Gas sensors are of great interest to portable and miniaturized sensing technologies with applications ranging from air quality monitoring to explosive detection and medical diagnostics, but the existing chemiresistive NO2 sensors still suffer from issues such as poor sensitivity, high operating temperature, and slow recovery. Herein, a high-performance NO2 sensors based on all-inorganic perovskite nanocrystals (PNCs) is reported, achieving room temperature operation with ultra-fast response and recovery time. After tailoring the halide composition, superior sensitivity of ≈67 at 8ppm NO2 is obtained in CsPbI2 Br PNC sensors with a detection level down to 2 ppb, which outperforms other nanomaterial-based NO2 sensors. Furthermore, the remarkable optoelectronic properties of such PNCs enable dual-mode operation, i.e., chemiresistive and chemioptical sensing, presenting a new and versatile platform for advancing high-performance, point-of-care NO2 detection technologies.