Lattice anchoring stabilizes solution-processed semiconductors.

The stability of solution-processed semiconductors remains an important area for improvement on their path to wider deployment. Inorganic caesium lead halide perovskites have a bandgap well suited to tandem solar cells1 but suffer from an undesired phase transition near room temperature2. Colloidal quantum dots (CQDs) are structurally robust materials prized for their size-tunable bandgap3; however, they also require further advances in stability because they are prone to aggregation and surface oxidization at high temperatures as a consequence of incomplete surface passivation4,5. Here we report 'lattice-anchored' hybrid materials that combine caesium lead halide perovskites with lead chalcogenide CQDs, in which lattice matching between the two materials contributes to a stability exceeding that of the constituents. We find that CQDs keep the perovskite in its desired cubic phase, suppressing the transition to the undesired lattice-mismatched phases. The stability of the CQD-anchored perovskite in air is enhanced by an order of magnitude compared with pristine perovskite, and the material remains stable for more than six months at ambient conditions (25 degrees Celsius and about 30 per cent humidity) and more than five hours at 200 degrees Celsius. The perovskite prevents oxidation of the CQD surfaces and reduces the agglomeration of the nanoparticles at 100 degrees Celsius by a factor of five compared with CQD controls. The matrix-protected CQDs show a photoluminescence quantum efficiency of 30 per cent for a CQD solid emitting at infrared wavelengths. The lattice-anchored CQD:perovskite solid exhibits a doubling in charge carrier mobility as a result of a reduced energy barrier for carrier hopping compared with the pure CQD solid. These benefits have potential uses in solution-processed optoelectronic devices.

Ligand Exchange at a Covalent Surface Enables Balanced Stoichiometry in III-V Colloidal Quantum Dots.

III-V colloidal quantum dots (CQDs) are promising semiconducting materials for optoelectronic applications; however, their strong covalent character requires a distinct approach to surface management compared with widely investigated II-VI and IV-VI CQDs-dots, which by contrast are characterized by an ionic nature. Here we show stoichiometric reconstruction in InAs CQDs by ligand exchange. In particular, we find that indium-carboxylate ligands, which passivate as-synthesized InAs CQDs and are responsible for In-rich surfaces, can be replaced by anionic ligands such as thiols. This enables the production of inks consisting of balanced-stoichiomety CQDs; this is distinct from what is observed in II-VI and IV-VI CQDs, in which thiols replace carboxylates. The approach enables the implementation of InAs CQD solids as the active layer in photodiode detectors that exhibit an external quantum efficiency of 36% at 930 nm and a photoresponse time of 65 ns, which is 4 times shorter than that of reference PbS CQD devices.

Bright and Stable Light-Emitting Diodes Based on Perovskite Quantum Dots in Perovskite Matrix.

Light-emitting diodes (LEDs) based on metal halide perovskite quantum dots (QDs) have achieved impressive external quantum efficiencies; however, the lack of surface protection of QDs, combined with efficiency droop, decreases device operating lifetime at brightnesses of interest. The epitaxial incorporation of QDs within a semiconducting shell provides surface passivation and exciton confinement. Achieving this goal in the case of perovskite QDs remains an unsolved challenge in view of the materials' chemical instability. Here, we report perovskite QDs that remain stable in a thin layer of precursor solution of perovskite, and we use strained QDs as nucleation centers to drive the homogeneous crystallization of a perovskite matrix. Type-I band alignment ensures that the QDs are charge acceptors and radiative emitters. The new materials show suppressed Auger bi-excition recombination and bright luminescence at high excitation (600 W cm-2), whereas control materials exhibit severe bleaching. Primary red LEDs based on the new materials show an external quantum efficiency of 18%, and these retain high performance to brightnesses exceeding 4700 cd m-2. The new materials enable LEDs having an operating half-life of 2400 h at an initial luminance of 100 cd m-2, representing a 100-fold enhancement relative to the best primary red perovskite LEDs.

Ligand-Assisted Reconstruction of Colloidal Quantum Dots Decreases Trap State Density.

Increasing the power conversion efficiency (PCE) of colloidal quantum dot (CQD) solar cells has relied on improving the passivation of CQD surfaces, enhancing CQD coupling and charge transport, and advancing device architecture. The presence of hydroxyl groups on the nanoparticle surface, as well as dimers-fusion between CQDs-has been found to be the major source of trap states, detrimental to optoelectronic properties and device performance. Here, we introduce a CQD reconstruction step that decreases surface hydroxyl groups and dimers simultaneously. We explored the dynamic interaction of charge carriers between band-edge states and trap states in CQDs using time-resolved spectroscopy, showing that trap to ground-state recombination occurs mainly from surface defects in coupled CQD solids passivated using simple metal halides. Using CQD reconstruction, we demonstrate a 60% reduction in trap density and a 25% improvement in charge diffusion length. These translate into a PCE of 12.5% compared to 10.9% for control CQDs.

Acid-Assisted Ligand Exchange Enhances Coupling in Colloidal Quantum Dot Solids.

Colloidal quantum dots (CQDs) are promising solution-processed infrared-absorbing materials for optoelectronics. In these applications, it is crucial to replace the electrically insulating ligands used in synthesis to form strongly coupled quantum dot solids. Recently, solution-phase ligand-exchange strategies have been reported that minimize the density of defects and the polydispersity of CQDs; however, we find herein that the new ligands exhibit insufficient chemical reactivity to remove original oleic acid ligands completely. This leads to low CQD packing and correspondingly low electronic performance. Here we report an acid-assisted solution-phase ligand-exchange strategy that, by enabling efficient removal of the original ligands, enables the synthesis of densified CQD arrays. Our use of hydroiodic acid simultaneously facilitates high CQD packing via proton donation and CQD passivation through iodine. We demonstrate highly packed CQD films with a 2.5 times increased carrier mobility compared with prior exchanges. The resulting devices achieve the highest infrared photon-to-electron conversion efficiencies (>50%) reported in the spectral range of 0.8 to 1.1 eV.

Metal-Organic Frameworks Mediate Cu Coordination for Selective CO2 Electroreduction.

The electrochemical carbon dioxide reduction reaction (CO2RR) produces diverse chemical species. Cu clusters with a judiciously controlled surface coordination number (CN) provide active sites that simultaneously optimize selectivity, activity, and efficiency for CO2RR. Here we report a strategy involving metal-organic framework (MOF)-regulated Cu cluster formation that shifts CO2 electroreduction toward multiple-carbon product generation. Specifically, we promoted undercoordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters. We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by separating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramagnetic resonance (EPR) and in situ X-ray absorption spectroscopy (XAS) experiments, we observed the formation of Cu clusters with low CN from distorted Cu dimers in HKUST-1 during CO2 electroreduction. These exhibited 45% C2H4 faradaic efficiency (FE), a record for MOF-derived Cu cluster catalysts. A structure-activity relationship was established wherein the tuning of the Cu-Cu CN in Cu clusters determines the CO2RR selectivity.

Extremely Small Pyrrhotite Fe7 S8 Nanocrystals with Simultaneous Carbon-Encapsulation for High-Performance Na-Ion Batteries.

Na/FeSx batteries have remarkable potential applicability due to their high theoretical capacity and cost-effectiveness. However, realization of high power-capability and long-term cyclability remains a major challenge. Herein, ultrafine Fe7 S8 @C nanocrystals (NCs) as a promising anode material for a Na-ion battery that addresses the above two issues simultaneously is reported. An Fe7 S8 core with quantum size (≈10 nm) overcomes the kinetic and thermodynamic constraints of the Na-S conversion reaction. In addition, the high degree of interconnection through carbon shells improves the electronic transport along the structure. As a result, the Fe7 S8 @C NCs electrode achieves excellent power capability of 550 mA h g-1 (≈79% retention of its theoretical capacity) at a current rate of 2700 mA g-1 . Furthermore, a conformal carbon shell acts as a buffer layer to prevent severe volume change, which provides outstanding cyclability of ≈447 mA h g-1 after 1000 cycles (≈71% retention of the initial charge capacity).

Asymmetric Metal-Carboxylate Complexes for Synthesis of InGaP Alloyed Quantum Dots with Blue Emission.

Indium phosphide (InP) quantum dots (QDs) have attracted significant interest as next-generation light-emitting materials. However, the synthesis of blue-emitting InP-based QDs has lagged behind that of established green- and red-emitting InP QDs. Herein, we present a strategy to synthesize blue-emitting QDs by forming an InGaP alloy composition. The introduction of asymmetric In-carboxylate and Ga-carboxylate complexes resulted in a balanced synthetic reactivity between In-P and Ga-P, leading to the formation of InGaP alloyed QDs. The resultant In1-xGaxP alloyed QDs exhibited a broad range of photoluminescence (PL) tunability, spanning from 535 nm (InP) to 465 nm (In0.62Ga0.38P), depending on the In/Ga ratio used in the synthesis. In contrast, synthesis with symmetric In-carboxylate and Ga-carboxylate complexes produced a core/shell structure of InP/GaP QDs, which did not exhibit a blue shift of the PL peak with Ga addition. By employing a core/shell structure of In0.62Ga0.38P/ZnS QDs, we achieved a PL quantum yield of 42% at 475 nm. This work highlights the material-processing strategy essential for forming alloyed structures in III-V ternary systems.

Synthesis and surface engineering of Ag chalcogenide quantum dots for near-infrared biophotonic applications.

Quantum dots (QDs), a novel category of semiconductor materials, exhibit extraordinary capabilities in tuning optical characteristics. Their emergence in biophotonics has been noteworthy, particularly in bio-imaging, biosensing, and theranostics applications. Although conventional QDs such as PbS, CdSe, CdS, and HgTe have garnered attention for their promising features, the presence of heavy metals in these QDs poses significant challenges for biological use. To address these concerns, the development of Ag chalcogenide QDs has gained prominence owing to their near-infrared emission and exceptionally low toxicity, rendering them suitable for biological applications. This review explores recent advancements in Ag chalcogenide QDs, focusing on their synthesis methodologies, surface chemistry modifications, and wide-ranging applications in biomedicine. Additionally, it identifies future directions in material science, highlighting the potential of these innovative QDs in revolutionizing the field.

Injectable composite hydrogels embedded with gallium-based liquid metal particles for solid breast cancer treatment via chemo-photothermal combination.

Photothermal therapy (PTT) holds great promise as a cancer treatment modality by generating localized heat at the tumor site. Among various photothermal agents, gallium-based liquid metal (LM) has been widely used as a new photothermal-inducible metallic compound due to its structural transformability. To overcome limitations of random aggregation and dissipation of administrated LM particles into a human body, we developed LM-containing injectable composite hydrogel platforms capable of achieving spatiotemporal PTT and chemotherapy. Eutectic gallium-indium LM particles were first stabilized with 1,2-Distearoyl-sn­glycero-3-phosphoethanolamine (DSPE) lipids. They were then incorporated into an interpenetrating hydrogel network composed of thiolated gelatin conjugated with 6-mercaptopurine (MP) chemodrug and poly(ethylene glycol)-diacrylate. The resulted composite hydrogel exhibited sufficient capability to induce MDA-MB-231 breast cancer cell death through a multi-step mechanism: (1) hyperthermic cancer cell death due to temperature elevation by near-infrared laser irradiation via LM particles, (2) leakage of glutathione (GSH) and cleavage of disulfide bonds due to destruction of cancer cells. As a consequence, additional chemotherapy was facilitated by GSH, leading to accelerated release of MP within the tumor microenvironment. The effectiveness of our composite hydrogel system was evaluated both in vitro and in vivo, demonstrating significant tumor suppression and killing. These results demonstrate the potential of this injectable composite hydrogel for spatiotemporal cancer treatment. In conclusion, integration of PTT and chemotherapy within our hydrogel platform offers enhanced therapeutic efficacy, suggesting promising prospects for future clinical applications. STATEMENT OF SIGNIFICANCE: Our research pioneers a breakthrough in cancer treatments by developing an injectable hydrogel platform incorporating liquid metal (LM) particle-mediated photothermal therapy and 6-mercaptopurine (MP)-based chemotherapy. The combination of gallium-based LM and MP achieves synergistic anticancer effects, and our injectable composite hydrogel acts as a localized reservoir for specific delivery of both therapeutic agents. This platform induces a multi-step anticancer mechanism, combining NIR-mediated hyperthermic tumor death and drug release triggered by released glutathione from damaged cancer populations. The synergistic efficacy validated in vitro and in vivo studies highlights significant tumor suppression. This injectable composite hydrogel with synergistic therapeutic efficacy holds immense promise for biomaterial-mediated spatiotemporal treatment of solid tumors, offering a potent targeted therapy for triple negative breast cancers.

Chiral 3D structures through multi-dimensional transfer printing of multilayer quantum dot patterns.

Three-dimensional optical nanostructures have garnered significant interest in photonics due to their extraordinary capabilities to manipulate the amplitude, phase, and polarization states of light. However, achieving complex three-dimensional optical nanostructures with bottom-up fabrication has remained challenging, despite its nanoscale precision and cost-effectiveness, mainly due to inherent limitations in structural controllability. Here, we report the optical characteristics of intricate two- and three-dimensional nanoarchitectures made of colloidal quantum dots fabricated with multi-dimensional transfer printing. Our customizable fabrication platform, directed by tailored interface polarity, enables flexible geometric control over a variety of one-, two-, and three-dimensional quantum dot architectures, achieving tunable and advanced optical features. For example, we demonstrate a two-dimensional quantum dot nanomesh with tuned subwavelength square perforations designed by finite-difference time-domain calculations, achieving an 8-fold enhanced photoluminescence due to the maximized optical resonance. Furthermore, a three-dimensional quantum dot chiral structure is also created via asymmetric stacking of one-dimensional quantum dot layers, realizing a pronounced circular dichroism intensity exceeding 20°.

Porous silicon nanowires for lithium rechargeable batteries.

Porous silicon nanowire is fabricated by a simple electrospinning process combined with a magnesium reduction; this material is investigated for use as an anode material for lithium rechargeable batteries. We find that the porous silicon nanowire electrode from the simple and scalable method can deliver a high reversible capacity with an excellent cycle stability. The enhanced performance in terms of cycling stability is attributed to the facile accommodation of the volume change by the pores in the interconnect and the increased electronic conductivity due to a multi-level carbon coating during the fabrication process.

Ultrahigh-resolution quantum dot patterning for advanced optoelectronic devices.

Quantum dots have attracted significant scientific interest owing to their optoelectronic properties, which are distinct from their bulk counterparts. In order to fully utilize quantum dots for next generation devices with advanced functionalities, it is important to fabricate quantum dot colloids into dry patterns with desired feature sizes and shapes with respect to target applications. In this review, recent progress in ultrahigh-resolution quantum dot patterning technologies will be discussed, with emphasis on the characteristic advantages as well as the limitations of diverse technologies. This will provide guidelines for selecting suitable tools to handle quantum dot colloids throughout the fabrication of quantum dot based solid-state devices. Additionally, epitaxially fabricated single-particle level quantum dot arrays are discussed. These are extreme in terms of pattern resolution, and expand the potential application of quantum dots to quantum information processing.

Modulating the folding and binding of peptides using a stimuli-responsive molecular tweezer.

This study presents the development of a ß-hairpin (tryptophan zipper, Trpzip)-based molecular tweezer (MT) that can control the folding and binding of α-helical peptides. When an α-helix isolated from the p53 protein was conjugated with Trpzip in an optimized macrocyclic structure, the folded ß-hairpin stabilized the helix conformation through the side chain-to-side chain stapling strategy, which notably enhanced target (hDM2) affinity of the peptide. On the other hand, the helicity and binding affinity were significantly reduced when the hairpin was unfolded by a redox stimulus. This stimulus-responsive property was translated into the effective capture and release of model multivalent biomaterials, hDM2-gold nanoparticle conjugates. Since numerous protein interactions are mediated by α-helical peptides, these results suggest that the ß-hairpin-based MT holds great potential to be utilized in various biomedical applications, such as protein interaction inhibition and cancer biomarker (e.g., circulating tumor cells and exosomes) detection.

Sequential Co-Passivation in InAs Colloidal Quantum Dot Solids Enables Efficient Near-Infrared Photodetectors.

III-V colloidal quantum dots (CQDs) are promising materials for optoelectronic applications, for they avoid heavy metals while achieving absorption spanning the visible to the infrared (IR). However, the covalent nature of III-V CQDs requires the development of new passivation strategies to fabricate conductive CQD solids for optoelectronics: this work shows herein that ligand exchanges, previously developed in II-VI and IV-VI quantum dots and employing a single ligand, do not fully passivate CQDs, and that this curtails device efficiency. Guided by density functional theory (DFT) simulations, this work develops a co-passivation strategy to fabricate indium arsenide CQD photodetectors, an approach that employs the combination of X-type methyl ammonium acetate (MaAc) and Z-type ligands InBr3 . This approach maintains charge carrier mobility and improves passivation, seen in a 25% decrease in Stokes shift, a fourfold reduction in the rate of first-exciton absorption linewidth broadening over time-under-stress, and leads to a doubling in photoluminescence (PL) lifetime. The resulting devices show 37% external quantum efficiency (EQE) at 950 nm, the highest value reported for InAs CQD photodetectors.

Solvent-Free Fabrication of Thick Electrodes in Thermoplastic Binders for High Energy Density Lithium-Ion Batteries.

The rapid development of electric vehicles has generated a recent demand for high energy density lithium-ion batteries (LIBs). One simple, effective way to enhance energy density of LIBs is to increase the thickness of electrodes. However, the conventional wet process used to fabricate thick electrodes involves the evaporation of large amounts of organic solvents, which causes an inhomogeneous distribution of conductive additives and binders. This weakens the mechanical and electrochemical network between active materials, resulting in poor electrochemical performance and structural degradation. Herein, we introduce a new strategy to produce homogeneous thick electrodes by using a dry, solvent-free process. Instead of using a conventional PVDF (polyvinylidene fluoride) binder, we employed a phenoxy resin as the binder in dry process for the first time. This thermoplastic binder exhibits better ductile properties than PVDF in the way that it generates a uniform network structure that connects the active materials during the hot press process. This enables the production electrochemically stable electrodes without using organic solvents, which record capacity retention rates of 73.5% over 50 cycles at a 40 mg/cm2 of thick electrodes. By contrast, thick electrodes produced with a PVDF binder via wet processing only have a capacity retention rate of 21.8% due to rapid structural degradation.

Synergetic Effect of Hybrid Conductive Additives for High-Capacity and Excellent Cyclability in Si Anodes.

Silicon is a promising anode material that can increase the theoretical capacity of lithium-ion batteries (LIBs). However, the volume expansion of silicon remains a challenge. In this study, we employed a novel combination of conductive additives to effectively suppress the volume expansion of Si during charging/discharging cycles. Rather than carbon black (CB), which is commonly used in SiO anodes, we introduced single-walled carbon nanotubes (SWCNTs) as a conductive additive. Owing to their high aspect ratio, CNTs enable effective connection of SiO particles, leading to stable electrochemical operation to prevent volume expansion. In addition, we explored a combination of CB and SWCNTs, with results showing a synergetic effect compared to a single-component of SWCNTs, as small-sized CB particles can enhance the interface contact between the conductive additive and SiO particles, whereas SWCNTs have limited contact points. With this hybrid conductive additive, we achieved a stable operation of full-cell LIBs for more than 200 cycles, with a retention rate of 91.1%, whereas conventional CB showed a 74.0% specific capacity retention rate.

Zinc Carboxylate Surface Passivation for Enhanced Optical Properties of In(Zn)P Colloidal Quantum Dots.

Indium phosphide (InP) colloidal quantum dots (CQDs) have generated great interest as next-generation light-emitting materials owing to their narrow emission spectra and environment-friendly components. The minimized surface defects is essential to achieve narrow full-width at half-maximum (FWHM) and high photoluminescence quantum yield (PLQY). However, InP CQDs are readily oxidized in ambient condition, which results in formation of oxidation defect states on the surface of InP CQDs. Herein, we introduce a strategy to successfully passivate the surface defects of InP core by zinc complexes. The zinc carboxylates passivation reduces FWHM of InP CQDs from 130 nm to 70 nm and increases PLQY from 1% to 14% without shelling. Furthermore, the photoluminescence (PL) peak has shifted from 670 nm to 510 nm with an increase of zinc carboxylates passivation, which suggests that excessive zinc carboxylates functions as a size-regulating reagent in the synthesis.

Fast Near-Infrared Photodetection Using III-V Colloidal Quantum Dots.

Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm2 V-1 s-1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 ns-the fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940 nm.

Facet-Oriented Coupling Enables Fast and Sensitive Colloidal Quantum Dot Photodetectors.

Charge carrier transport in colloidal quantum dot (CQD) solids is strongly influenced by coupling among CQDs. The shape of as-synthesized CQDs results in random orientational relationships among facets in CQD solids, and this limits the CQD coupling strength and the resultant performance of optoelectronic devices. Here, colloidal-phase reconstruction of CQD surfaces, which improves facet alignment in CQD solids, is reported. This strategy enables control over CQD faceting and allows demonstration of enhanced coupling in CQD solids. The approach utilizes post-synthetic resurfacing and unites surface passivation and colloidal stability with a propensity for dots to couple via (100):(100) facets, enabling increased hole mobility. Experimentally, the CQD solids exhibit a 10× increase in measured hole mobility compared to control CQD solids, and enable photodiodes (PDs) exhibiting 70% external quantum efficiency (vs 45% for control devices) and specific detectivity, D* > 1012  Jones, each at 1550 nm. The photodetectors feature a 7 ns response time for a 0.01 mm2 area-the fastest reported for solution-processed short-wavelength infrared PDs.