Ionic liquid assisted preparation and modulation of the photoluminescence kinetics for highly efficient CsPbX3 nanocrystals with improved stability

Enhancing the performance of PbS:CsPbBr3 bulk-heterojunction photodetectors by treating with imidazolium-based ionic liquids

All-inorganic lead halide perovskites and quantum dots (QDs) have gained significant attention since their emergence, owing to their immense potential for applications in optoelectronic devices. Here, enhanced-performance broadband photodetectors based on the bulk-heterostructure of a CsPbBr3 perovskite and PbS colloidal quantum dots (CQDs) are presented, and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF4) ionic liquids as a dual-purpose additive were introduced in the blended film to regulate the surface of QDs by facilitating surface passivation, adjusting energy levels, and coupling with longer alkyl chains as compared to iodide ions (I-). As a result, a superior-quality bulk-heterostructure based photodetector with long-term stability was obtained, showing outstanding performance in photodetection across the visible to near-infrared wavelength range, demonstrating a high photoresponsivity of 22.4 A W-1 with a response time of 16.2 ms and a specific detectivity of 1.58 × 1014 Jones under 405 nm illumination. Thus, this work provides a novel modification strategy for PbS:CsPbBr3 as a promising material for novel optoelectronics.

The surface chemistry of ionic liquid-treated CsPbBr3 quantum dots

The power conversion efficiencies of lead halide perovskite thin film solar cells have surged in the short time since their inception. Compounds, such as ionic liquids (ILs), have been explored as chemical additives and interface modifiers in perovskite solar cells, contributing to the rapid increase in cell efficiencies. However, due to the small surface area-to-volume ratio of the large grained polycrystalline halide perovskite films, an atomistic understanding of the interaction between ILs and perovskite surfaces is limited. Here, we use quantum dots (QDs) to study the coordinative surface interaction between phosphonium-based ILs and CsPbBr3. When native oleylammonium oleate ligands are exchanged off the QD surface with the phosphonium cation as well as the IL anion, a threefold increase in photoluminescent quantum yield of as-synthesized QDs is observed. The CsPbBr3 QD structure, shape, and size remain unchanged after ligand exchange, indicating only a surface ligand interaction at approximately equimolar additions of the IL. Increased concentrations of the IL lead to a disadvantageous phase change and a concomitant decrease in photoluminescent quantum yields. Valuable information regarding the coordinative interaction between certain ILs and lead halide perovskites has been elucidated and can be used for informed pairing of beneficial combinations of IL cations and anions.

Green synthesis of highly stable CsPbBr3 perovskite nanocrystals using natural deep eutectic solvents as solvents and surface ligands

Perovskite nanocrystals (PNCs) have attracted widespread attention as promising materials for the optoelectronic field due to their remarkable photophysical properties and structural tunability. However, their poor stability and the use of toxic organic solvents in the preparation process have severely restricted their practical applications. Herein, a facile, rapid and toxic organic solvent-free synthesis strategy of CsPbBr₃ PNCs was developed for the first time via the ligand-assisted reprecipitation (LARP) method using natural deep eutectic solvents (NADESs) as solvents and surface ligands. In this method, the NADESs not only functioned as solvents for green synthesis, but also served simultaneously as surface ligands of CsPbBr₃ PNCs to significantly improve their optical properties and stability. The as-synthesized CsPbBr₃ PNCs exhibited high photoluminescence quantum yield (PLQY, ∼96.8%), narrow full width at half-maximum (FWHM, ∼18.8 nm) and a high stability that retained 82.9% of PL intensity after 70 days. This work provides a new strategy for the green synthesis of PNCs, which promises feasibility for the industrial large-scale synthesis of high-quality PNCs.

Environmentally Friendly Syntheses of Self-Healed and Printable CsPbBr3 Nanocrystals

Generally, solvents used to synthesize perovskite NCs are toxic, which leads to waste liquid pollution and environmental degradation. Herein, we developed a novel environmentally friendly polar solvent method to synthesize CsPbBr₃ nanocrystals (NCs). Over 65% photoluminescence quantum yield (PLQYs) for NCs could be maintained over 45-850 h of storage time, and a maximum was 78% at 750 h. Such amazing stability in polar solvents is dominated by a ripening process, which heals surface defects. Additionally, their solid films also exhibited good moisture stability. Furthermore, CsPbBr₃ NCs were applied to inkjet-printing to prepare high-quality patterned films.

Ultralow-cost portable device for cesium detection via perovskite fluorescence

Public anxiety and concern from cesium pollution in oceans have been back on the agenda since tons of nuclear waste water were announced to be poured into oceans. Cesium ion can easily enter organisms and bioaccumulate in animals and plants, thus its harm is chronic to humans through food chains. Here we showed a kind of hybrid ionic liquid membrane (HILM) for detection of cesium ion in seawater through CsPbBr₃ perovskite fluorescence. With sustainability in mind, HILM was built frugally. The lowest cost of HILM is below 3 cents per piece. The HILM can detect cesium ion quickly with eye-readable fluorescence signal. Ultracheap, portable, easy-to-use on-site detection device could offer benefit for personal security and applications in environment science and ecology in the future decades.

Ionic Liquids Modulating CsPbI3 Colloidal Quantum Dots Enable Improved Mobility for High-Performance Solar Cells

Colloidal all-inorganic CsPbI₃ perovskite quantum dots (PQDs) have shown tremendous potential in photovoltaic applications in recent years due to their outstanding optoelectronic properties that general metal halide perovskites offer, along with the added advantages that originates from size reduction and the quantum confinement effect. However, the issue of low carrier mobility in PQD films caused by insulating organic ligands capped on the PQD surface still remains to be addressed while aiming for high-efficiency PQD solar cells. Herein, we propose a novel strategy that takes benefits of ionic liquids, which can offer the high polarity and the electron donating ability to boost the mobility of PQD films in photovoltaic devices. Specifically, 1-propyl-3-methylimidazolium iodide to modulate the colloidal CsPbI₃ PQD surface and couple QDs is demonstrated for the first time. The lone pair electrons on the nitrogen of the imidazole ring within the ionic liquid binds to the empty nonbonding surface orbitals of CsPbI₃ PQDs while the long-chain insulating ligands are replaced, which enables not only efficient charge transport but also reduced defect density in the assembled PQD solid films. The resulting CsPbI₃ PQD solar cell shows a significant increase in efficiency with suppressed hysteresis, indicating the impressive potential of this strategy for developing highly efficient PQD solar cells.

Highly luminescent and stable quasi-2D perovskite quantum dots by introducing large organic cations

Herein, ultra-stable quasi-two-dimensional perovskite quantum dots (quasi-2D PQDs) are synthesized by introducing the butylamine cation (BA⁺) into the methylamine lead bromide perovskite (MAPbBr₃). By reducing the dimensionality of the perovskite structure, the quasi-2D perovskite (BA)₂(MA) _x-1Pb _x Br_3x+1 presents higher luminescence efficiency and better environmental stability than traditional 3D perovskites, which is mainly because the dimensionality-reduced perovskite has higher exciton binding energy and formation energy. Under an optimal MA : BA ratio of 1 : 1, the quasi-2D perovskite exhibits about four times higher luminescence efficiency (PLQY = 49.44%) than pristine MAPbBr₃; meanwhile it emits stable luminescence in an environment with 80% humidity for 50 days. Most importantly, carbon quantum dot (CQD) doping has also been applied in this work, which effectively passivates the defects of (BA)₂(MA) _x-1Pb _x Br_3x+1 via H-bond interaction, further improving the stability of the perovskite in water. Inspired by the superior performances of the proposed quasi-2D nanomaterial, a novel colorimetric method based on halide ion exchange has been developed for H₂O₂ detection, which also demonstrates that PQDs show significant potential in the field of environmental monitoring.

The biocompatible validity of amino acid ionic liquid mediated gold nanoparticles for enhanced activity and structural stability of papain

During the past few decades, gold nanoparticles (AuNPs) have attracted a lot of attention owing to their biomedical applications, like therapeutics and drug delivery; however, the detailed biomolecular interactions and structural alteration of naturally occurring biomolecules, such as enzymes, in AuNPs remain unknown. The effects of various additives on the thermal and structural properties, and activity of proteins/enzymes have been scavenged and communicated intensively in the literature; however, the synthesis of ionic liquid (IL) mediated AuNPs solely for the purpose of enzyme activity boosting and stability modulation has not yet been reported. In the current study, we explore the role of cholinium tryptophan [CHO][Trp] and tetraethyl tryptophan [TEA][Trp]IL-mediated gold nanoparticles (AuNPs) on the activity enhancement and structural stability of papain. Our results showed that [CHO][Trp] and [TEA][Trp]IL-mediated AuNPs efficiently increased the proteolytic activity of papain, which was increased from 100 to 206% for [CHO][Trp]IL-mediated AuNPs and enhanced from 100 to 136% in [TEA][Trp]IL-mediated AuNPs. Additionally, extended differential scanning calorimetry (DSC) results showed that these AAIL-mediated AuNPs maintained the thermal stability of papain only at lower concentration. Spectroscopic studies conclude that the tryptophan (Trp) group of papain is expanded more towards the polar environment in the presence of [CHO][Trp] as compared to [CHO][Trp]IL mediated AuNPs. The far CD spectral and deconvoluted results show that the α-helical and β-turn contents of the secondary structure of papain are preserved to a large extent; however, disruption in the β-sheet has been observed for both AAIL-mediated AuNPs. Dynamic light scattering (DLS), zeta potential and transmission electron microscopy (TEM) results illustrate the distinct interactive behavior of papain for both types of AAIL-mediated AuNPs. The immobilization of papain is higher on [CHO][Trp]AuNPs compared to [TEA][Trp]AuNPs and papain surrounds [CHO][Trp]AuNPs on all sides, which is lacking in [TEA][Trp]AuNPs.

A new route for the shape differentiation of cesium lead bromide perovskite nanocrystals with near-unity photoluminescence quantum yield

The ongoing interest in all-inorganic cesium lead bromide perovskite nanocrystals (CsPbBr3 NCs) is mainly due to their optical properties, in particular their high photoluminescence quantum yields (PLQYs). Three-precursor synthetic methods, in which the sources of the three elements (cesium, lead and bromine) constituting the perovskite scaffold are chemically independent, often succeed in the achievement of near-unity PLQY perovskite NCs. However, this class of synthetic approaches precludes the accessibility to crystal morphologies different from the traditional cuboidal ones. In order to upgrade three-precursor synthetic schemes to obtain more sophisticated morphologies - such as rods - we propose a conceptually original synthetic methodology, in which a potentially controllable stage of the reaction anticipates the fast crystallization promoted by cesium injection. To this purpose, lead oxide, 1-bromohexane (at different molar ratios with respect to lead) and the ligands (oleic acid and a suitable amine) in 1-octadecene are reacted at 160 °C for an incubation period of 30 min before cesium injection. During this stage and at high C6H13Br/PbO molar ratios, the bromide release from reactions between the ligands and 1-bromohexane promotes the evolution of [PbBr(2+n)]n- species as well as of two-dimensional [(RNH3)2(PbBr4)]n structures with a rod-like shape (aspect ratios ∼10). These structures act as the templating agents for the subsequent crystallization promoted by cesium injection, ensuring the formation of near-unity PLQY nanorods in the presence of decylamine. Conversely, the pronounced decomposition of the preformed [(RNH3)2(PbBr4)]n structures preludes to the formation of near-unity PLQY nanocubes in the presence of hexylamine. The amine choice exerts also an important role in the emission stability of the corresponding NCs, since the nanocubes prepared in the presence of hexylamine maintain their near-unity PLQYs up to 90 days under ambient conditions. In addition to the long-term PLQY stability, the nanorods prepared with decylamine also exhibit a remarkable resistance to the presence of water, due to the compact and hydrophobic organic shell passivating the NC surface. These findings can contribute to the development of innovative synthetic methodologies for controlling the shape and stability of near-unity PLQY perovskite NCs.