Colloidal Precursors Research Articles

Tin oxides@stannous pyrophosphate colloidal quantum dots as multifunctional electron transporting layer for efficient and stable perovskite solar cells

Perovskite solar cells (PSCs) are anticipated to spearhead the revolution in solar energy technology. Engineering the electron transporting layer (ETL)/perovskite heterointerface is known to be a key point for further high-performance PSCs because it determines the main charge transporting and energy losses. However, the most advanced SnO2 colloidal precursors tend to exhibit agglomeration and structural flaws, thereby deteriorating the morphology and electronic mass of the obtained ETL. Here, we polished the microstructure of the SnO2 surface by self-assembling SnO2@Sn2P2O7 quantum dots (SPOS), which is synthesized by the chemical reaction between hypophosphoric acid (H3PO2) and SnO2. The Sn2P2O7 was synthesized on the SnO2 surface, terminating the surface dangling bonds and resulting in steady SPOS quantum dots with smooth microstructure. The SPOS ETL with good optical and electrical properties as well as matched bandgap alignment with perovskite, yielding an improved power conversion efficiency of 23.35% for PSCs. Moreover, due to the suppression of defect-induced deprotonation reactions, the SPOS-PSCs exhibit favorablelongstability than the SnO2-PSCs. This work demonstrates that the surface reconstruction of the ETL is crucial for enhancing the power conversion efficiency and stability of PSCs.

Unveiling the effect of hypophosphorous acid for the growth of high quality Cs3Cu2I5 single crystals

The zero-dimensional copper halide perovskite Cs3Cu2I5 displays extraordinary luminescence and scintillation characteristics, and high-quality crystals are extremely desirable for exploring the commercial applications. Currently, the most critical issue in the solution growth of Cs3Cu2I5 crystals is the easy oxidation of halides, which significantly hinders the optimization of crystal qualities. The hypophosphorous acid (H3PO2) has been applied to inhibit the oxidation, nevertheless, the related mechanism is elusive and has been largely ignored. Herein, Cs3Cu2I5 crystals have been grown from N, N-Dimethylformamide (DMF) solvent by the antisolvent vapor-assisted crystallization (AVC) method. It is verified that H3PO2 effectively prevents the oxidation of Cs3Cu2I5 by rapidly reducing Cu2+ and I3−, maintaining the stability of the precursor solution and continuously suppressing oxidation during the whole growth process. Meanwhile, by increasing the acidity of the solution, H3PO2 dissolve precursor colloids and efficiently enhance the solubility of halides. Thus, the addition of H3PO2 favors the rapid growth of centimeter-sized Cs3Cu2I5 crystals with well-defined crystallographic planes within several days. As excellent gamma ray scintillator, the crystal exhibits high light yield of 38000 photons/MeV, with energy resolution of 5.6 % under 662 keV radiation from a 137Cs source. This work deeply elucidates new insight into the critical effect of H3PO2 in the DMF based solution crystal growth, facilitating the preparation of large-size and high-performance copper halide perovskite crystals.

Modulating the size distribution of preformed BaHfO3 nanocrystals towards effective flux pinning in MOD-derived YBCO-coated conductors

The added BaMO3 (BMO, M = Zr, Hf) nanocrystals into REBa2Cu3O7−δ (REBCO, RE = Y or other rare earth) superconducting films by the technology of preformed nanocrystal addition from colloidal precursor solutions have coarsened after sintering of the REBCO films, which limit the BMO size control and flux pinning enhancement. In the present work, the evolution of the size of BaHfO3 (BHO) nanocrystals in the YBCO films is studied. The collection process of BHO nanocrystals is optimized to successfully separate BHO with an average size of 6 nm into two parts with average sizes of 4.5 nm and 7.7 nm, respectively. The evolution of three different BHO sizes in YBCO superconducting films with a thickness of 2.2 μm and 10 mol% addition reveals that the small-size preformed nanocrystals decomposed at high temperatures to release Hf ions, resulting in the coarsening of other preformed BHO nanocrystals. After modulating the BHO size by reducing the amount of small-size BHO, the coarsening factor is reduced from 1.6 to 1.1, leading to a better in-field performance, especially at low temperatures. At 30 K@1 T, the critical current density (J c) of the 7.7 nm BHO-added YBCO increases by 23% and 50% than cases of 6 nm and 4.5 nm, respectively, being of great guiding value in the technology of performed nanocrystal addition.

The influence of deuterium on sodium mobility and viscosity of colloidal precursor suspensions yielding template-free nanosized zeolites

The isotopic substitution in chemistry is characterized by two main effects, i.e., the kinetic isotope effect (KIE), associated with differences in the reaction rates, and the geometric isotope effect (GIE) related to crystallographic features. In this work, considering the difference in the weight of deuterium (D) compared to the weight of hydrogen (H), we use the isotopic substitution to investigate the crystallisation mechanism of template-free nanosized faujasite (FAU) type zeolite in colloidal precursors. Тhe basic hydrothermal synthesis solvent - water (H2O), is substituted with heavy water (D2O), aiming to understand the isotopic influence and the effect of H-bond networks on the zeolite crystallisation. The crystallinity, viscosity, conductivity, chemical composition, morphology and local order of the FAU zeolites synthesized in both hydrated (H) and deuterated (D) medium are evaluated with X-ray diffraction, TEM microscopy, EDX and ICP analysis, FT-IR and solid-state NMR spectroscopy. The structural directing agent - Na+, exhibits a lower mobility in the deuterated medium, because of a characteristic higher viscosity compared to hydrated medium. This leads to a slower nucleation and crystallisation in the initial stages of hydrothermal treatment in the colloidal suspensions but also to a significant difference in the Al distribution.

Modulating Crystallization and Defect Passivation by Butyrolactone Molecule for Perovskite Solar Cells.

The attainment of a well-crystallized photo-absorbing layer with minimal defects is crucial for achieving high photovoltaic performance in polycrystalline solar cells. However, in the case of perovskite solar cells (PSCs), precise control over crystallization and elemental distribution through solution processing remains a challenge. In this study, we propose the use of a multifunctional molecule, α-amino-γ-butyrolactone (ABL), as a modulator to simultaneously enhance crystallization and passivate defects, thereby improving film quality and deactivating nonradiative recombination centers in the perovskite absorber. The Lewis base groups present in ABL facilitate nucleation, leading to enhanced crystallinity, while also retarding crystallization. Additionally, ABL effectively passivates Pb2+ dangling bonds, which are major deep-level defects in perovskite films. This passivation process reduces recombination losses, promotes carrier transfer and extraction, and further improves efficiency. Consequently, the PSCs incorporating the ABL additive exhibit an increase in conversion efficiency from 18.30% to 20.36%, along with improved long-term environmental stability. We believe that this research will contribute to the design of additive molecular structures and the engineering of components in perovskite precursor colloids.

Precursor Solution Aging: A Universal Strategy Modulating Crystallization of Two-Dimensional Tin Halide Perovskite Films

Two-dimensional (2D) tin (Sn2+)-based perovskites have achieved remarkable advancements in (opto)electronic devices. However, fabricating high-quality and reproducible Sn halide perovskite thin films remains challenging due to uncontrollably fast crystallization. To overcome this issue, dimethyl sulfoxide has been incorporated as an indispensable strategy to form Lewis acid–base adducts but also has been proven to induce an irreversible Sn2+ oxidization effect. As the crystalline films grow directly from solution, a better understanding of precursor colloidal chemistry and the film formation process is critical. In this study, we report a universal solution aging approach to fabricate high-quality and reliable 2D Ruddlesden–Popper and Dion–Jacobson Sn2+ perovskite films and devices. The proper solution aging stabilizes the precursor colloids by eliminating aggregated complex and unreacted precursor clusters in the fresh precursor, leading to homogeneous nucleation/crystallization and film growth. The precursor aging reduced film defect density by nearly 2 orders of magnitude and improved charge transport mobility by over 5 times. This study can inspire the community to understand the deposition mechanism for high-quality Sn2+ perovskite thin films and promote the development of high-performance and reproducible Sn2+ perovskite based (opto)electronic devices.

Hierarchical Structures Formed in an Atmospheric Pressure Plasma Jet by Polymerization from an Aerosol of Oxalic Acid Stabilized WO3–x Nanosheet Colloids: Toward High-Performance Electrochemical Devices and Sensors

The development of microstructures which combine high total surface area and high porosity is crucial for technologies such as electrocatalysis, electrochromics, and sensors. High deposition rate, composition control of deposition, and low processing temperature to retain active compositions are also desirable. To this end, this study describes combining colloidal sol chemistry with a nonthermal atmospheric pressure dielectric barrier discharge plasma jet to print hybrid inorganic/organic tungsten trioxide/oxalic acid (WO3–x/OA) microspheres. Injection of an aerosol of oxalic acid stabilized colloidal tungstic acid into an atmospheric pressure plasma jet results in the deposition of spherical structures in which the colloid is trapped within a plasma-polymerized organic shell. Subsequent low-temperature sintering produces hierarchical spherical shell-like structures comprising tungsten oxide nanosheets. Alteration of the gas flow rate changes the composition of the deposited material. The method has promise for the general preparation from colloidal precursors of porous materials of controlled morphology and composition with hierarchical microstructures, such as are required for applications in electrochemical devices and sensors which need a high ratio of surface area to volume and connectivity throughout the structure, yet also need a microstructure which is open for rapid exchange of reactants.

Reduced VOC Deficit of Mixed Lead-Tin Perovskite Solar Cells via Strain-Releasing and Synergistic Passivation Additives.

The power conversion efficiency (PCE) of tin-lead perovskite solar cells (PSCs) is normally lower than that of Pb cells, mainly due to greater open circuit voltage (VOC ) losses. Herein, the additive 2,6-diaminopyridine (TNPD) is designed to anchor on the surface of the perovskite precursor colloid as nucleating agent to modulate the growth of Pb-Sn perovskites. It is observed that the TNPD not only effectively induces crystal growth during the nucleation stage, remaining on the crystal surface and ultimately passivating the resulting perovskite films, but also releases the micro-strain generated during the film growth. Furthermore, TNPD could lower the defect density (Sn4+ amount) by screening the perovskite against oxygen and by synergistically bonding with undercoordinated Sn/Pb on the surface. Finally, a high VOC of 0.85V is obtained, corresponding to a voltage deficit of 0.41V using a perovskite absorber with a bandgap of 1.26eV, and a high PCE (20.35%) reported so far for Pb-Sn PSCs. Moreover, the stability of the TNPD-incorporated device is significantly improved, and the PCE maintains 50% of the initial value after about 1000 h storage in glovebox without encapsulated, in comparison to that of the control device (about 700 h, maintaining 30% of the initial value).

Zwitterions Narrow Distribution of Perovskite Quantum Wells for Blue Light-Emitting Diodes with Efficiency Exceeding 15.

While quasi-two-dimensional (quasi-2D) perovskites have emerged as promising semiconductors for light-emitting diodes (LEDs), the broad-width distribution of quantum wells hinders their efficient energy transfer and electroluminescence performance in blue emission. In particular, the underlying mechanism is closely related to the crystallization kinetics and has yet to be understood. Here for the first time, the influence of bifunctional zwitterions with different coordination affinity on the crystallization kinetics of quasi-2D perovskites is systematically investigated. The zwitterions can coordinate with Pb2+ and also act as co-spacer organic species in quasi-2D perovskites, which collectively inhibit the aggregation of colloidal precursors and shorten the distance of quantum wells. Consequently, restricted nucleation of high-n phases and promoted growth of low-n phases are achieved with moderately coordinated zwitterions, leading to the final film with a more concentrated n distribution and improved energy transfer efficiency. It thus enables high-efficiency blue LEDs with a recorded external quantum efficiency of 15.6% at 490nm, and the operation stability has also been prolonged to 55.3min. These results provide useful directions for tuning the crystallization kinetics of quasi-2D perovskites, which is expected to lead to high-performance perovskite LEDs.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Spontaneous Hetero-attachment of Single-Component Colloidal Precursors for the Synthesis of Asymmetric Au-Ag2X (X = S, Se) Heterodimers.

Finding simple, easily controlled, and flexible synthetic routes for the preparation of ternary and hybrid nanostructured semiconductors is always highly desirable, especially to fulfill the requirements for mass production to enable application to many fields such as optoelectronics, thermoelectricity, and catalysis. Moreover, understanding the underlying reaction mechanisms is equally important, offering a starting point for its extrapolation from one system to another. In this work, we developed a new and more straightforward colloidal synthetic way to form hybrid Au-Ag2X (X = S, Se) nanoparticles under mild conditions through the reaction of Au and Ag2X nanostructured precursors in solution. At the solid-solid interface between metallic domains and the binary chalcogenide domains, a small fraction of a ternary AuAg3X2 phase was observed to have grown as a consequence of a solid-state electrochemical reaction, as confirmed by computational studies. Thus, the formation of stable ternary phases drives the selective hetero-attachment of Au and Ag2X nanoparticles in solution, consolidates the interface between their domains, and stabilizes the whole hybrid Au-Ag2X systems.

Helical microstructures in molluscan biomineralization are a biological example of close packed helices that may form from a colloidal liquid crystal precursor in a twist–bend nematic phase

We demonstrate that nature has produced a close-packed helical twisted filamentous material in the biomineralization of the mollusc. In liquid crystals, twist-bend nematics have been predicted and observed. We present and analyse evidence that the helical biomineral microstructure of mollusc shells may be formed from such a liquid-crystal precursor.

Multi-functional Strategy: Ammonium Citrate-Modified SnO2 ETL for Efficient and Stable Perovskite Solar Cells.

The tin oxide (SnO2) electron transport layer (ETL) plays a crucial role in perovskite solar cells (PSCs). However, the heterogeneous dispersion of commercial SnO2 colloidal precursors is far from optimized, resulting in dissatisfied device performance with SnO2 ETL. Herein, a multifunctional modification material, ammonium citrate (TAC), is used to modify the SnO2 ETL, bringing four benefits: (1) due to the electrostatic interaction between TAC molecules and SnO2 colloidal particles, more uniformly dispersed colloidal particles are obtained; (2) the TAC molecules distributed on the surface of SnO2 provide nucleation sites for the perovskite film growth, promoting the vertical growth of the perovskite crystal; (3) TAC-doped SnO2 shows higher electron conductivity and better film quality than pristine SnO2 while offering better energy-level alignment with the perovskite layer; and (4) TAC has functional groups of C═O and N-H containing lone pair electrons, which can passivate the defects on the surface of SnO2 and perovskite films through chemical bonding and inhibit the device hysteresis. In the end, the device based on TAC-doped ETL achieved an increased power conversion efficiency (PCE) of 21.58 from 19.75% of the reference without such treatment. Meanwhile, the PSCs using the TAC-doped SnO2 as the ETL maintained 88% of their initial PCE after being stored for about 1000 h under dark conditions and controlled RH of 10-25%.

In-situ peptization of WO3 in alkaline SnO2 colloid for stable perovskite solar cells with record fill-factor approaching the shockley–queisser limit

SnO2-based electron transport layers (ETLs) offer outstanding band alignment, excellent chemical and UV stability, high transmittance, high conductivity, and processability at low temperatures. However, unfortunately, the state-of-the-art SnO2 colloid precursor suffered from agglomeration over time and structural defects such as dangling hydroxyl groups and oxygen vacancies, which deteriorate both the morphology and electronic quality of the resulting ETL. Especially, these trap states near the valence band can hinder charge extraction and transport of electrons to couple with non-radiative recombination loss. Here, we introduce a novel WO3 @SnO2 nanocomposite ETL, which is synthesized by in situ peptizations of WO3 in commercial alkaline SnO2 colloid nanocrystals. The hydrated (peptized) WO3 forms H2WO4 (WO42-) to effectively stabilize the SnO2 nanocrystals in the dispersion and bind to the defect sites. Intriguingly, the H2WO4 converts back to the WO3 phase to form nano-heterostructured composite with SnO2 particles during the process of film fabrication, further promoting passivation and charge extraction. Through the novel method, we could achieve molecular level passivation of SnO2 layer by WO3, and a power conversion efficiency of 23.6% for a 0.1 cm2 PSC device with ultra-high FF of 85.8% was demonstrated. Furthermore, a modified detailed balance model was used to verify the drastically lessened surface & bulk defect-induced recombination loss in WO3 @SnO2 based devices. Finally, the corresponding unencapsulated cell retained ~91% of its initial efficiency after 2000 h of damp exposure. This work provides a promising method to access the Shockley–Queisser limit of fill factor for single-junction PSC.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Stable Metal–Halide Perovskite Colloids in Protic Ionic Liquid

Accelerating the Crystallization of Zeolite SSZ‐13 with Polyamines

AbstractTailoring processes of nucleation and growth to achieve desired material properties is a pervasive challenge in synthetic crystallization. In systems where crystals form via nonclassical pathways, engineering materials often requires the controlled assembly and structural evolution of colloidal precursors. In this study, we examine zeolite SSZ‐13 crystallization and show that several polyquaternary amines function as efficient accelerants of nucleation, and, in selected cases, tune crystal size by orders of magnitude. Among the additives tested, polydiallyldimethylammonium (PDDA) was found to have the most pronounced impact on the kinetics of SSZ‐13 formation, leading to a 4‐fold reduction in crystallization time. Our findings also reveal that enhanced nucleation occurs at an optimal PDDA concentration where a combination of light‐scattering techniques demonstrate these conditions lead to polymer‐induced aggregation of amorphous precursors and the promotion of (alumino)silicate precipitation from the growth solution. Here, we show that relatively low concentrations of polymer additives can be used in unique ways to dramatically enhance SSZ‐13 crystallization rates, thereby improving the overall efficiency of zeolite synthesis.

Accelerating the Crystallization of Zeolite SSZ-13 with Polyamines.

Tailoring processes of nucleation and growth to achieve desired material properties is a pervasive challenge in synthetic crystallization. In systems where crystals form via nonclassical pathways, engineering materials often requires the controlled assembly and structural evolution of colloidal precursors. In this study, we examine zeolite SSZ-13 crystallization and show that several polyquaternary amines function as efficient accelerants of nucleation, and, in selected cases, tune crystal size by orders of magnitude. Among the additives tested, polydiallyldimethylammonium (PDDA) was found to have the most pronounced impact on the kinetics of SSZ-13 formation, leading to a 4-fold reduction in crystallization time. Our findings also reveal that enhanced nucleation occurs at an optimal PDDA concentration where a combination of light-scattering techniques demonstrate these conditions lead to polymer-induced aggregation of amorphous precursors and the promotion of (alumino)silicate precipitation from the growth solution. Here, we show that relatively low concentrations of polymer additives can be used in unique ways to dramatically enhance SSZ-13 crystallization rates, thereby improving the overall efficiency of zeolite synthesis.

A microfluidics‐dispensing‐printing strategy for Janus photonic crystal microspheres towards smart patterned displays

AbstractFrom the implementation point of view, the printable magnetic Janus colloidal photonic crystals (CPCs) microspheres are highly desirable. Herein, we developed a dispensing‐printing strategy for magnetic Janus CPCs display via a microfluidics‐automatic printing system. Monodisperse core/shell colloidal particles and magnetic Fe3O4 nanoparticles precursor serve as inks. Based on the equilibrium of three‐phase interfacial tensions, Janus structure is successfully formed, followed by UV irradiation and self‐assembly of colloid particle to generate magnetic Janus CPCs microspheres. Notably, this method shows distinct superiority with highly uniform Janus CPCs structure, where the TMPTA/Fe3O4 hemisphere is in the bottom side while CPCs hemisphere is in the top side. Thus, by using Janus CPCs microspheres with two different structural colors as pixel points, a pattern with red flower and green leaf is achieved. Moreover, 1D linear Janus CPCs pattern encapsulated by hydrogel is also fabricated. Both the color and the shape can be changed under the traction of magnets, showing great potentials in flexible smart displays. We believe this work not only offers a new feasible pathway to construct magnetic Janus CPCs patterns by a dispensing‐printable fashion, but also provides new opportunities for flexible and smart displays.

Silicalite-1 formation in acidic medium: Synthesis conditions and physicochemical properties

Zeolites are the catalytic materials that are widly applied in the processing of conventional and renewable fuels and chemicals. The present study provides a comprehensive analysis of the factors controlling the acidic medium synthesis of high silica silicalite-1 zeolite. The effect of various silica sources (TEOS, fumed and colloidal silica) and alkali metal cations (Na and K) on the silicalite-1 formation is studied. The efficiency of different types of seeds (micron-sized, nanosized, and silicalite-1 amorphous colloidal precursor) on the silicalite-1 crystal growth kinetics and crystal size formed under acidic conditions is also investigated. Further, the zeolite crystallization kinetics under acidic, neutral, and basic conditions is compared. The obtained highly crystalline samples are used to compare the physicochemical properties of zeolites synthesized in acidic, neutral, and basic medium. Thus, the crystallinity, thermal stability, and local order in silicalite-1 samples synthesized in the (2–12) pH range are evaluated.