279 Search Results

Two-dimensional (2D) colloidal nanocrystals deliver quantum-well like performance at relatively low processing costs, making them an attractive material platform for future LEDs, lasers, and photodetectors. However, their sheet-like morphology hinders the formation of ordered, densely packed films - an essential requirement for electrically interfaced devices. Here, we address this limitation by introducing semiconductor quantum cubes (QCs) in which 2D CdSe nanosheets are conformally grown on six faces of CdS cubic scaffolds. This architecture preserves the excitonic physics of 2D CdSe while leveraging the mechanical rigidity and self-assembly of 3D nanocubes, enabling regular, close-packed films with improved electronic coupling and conductivitymore » in films. Extending CdS/CdSe QCs into a shelled CdS/CdSe/CdS quantum wells leads to nanoplatelet-like confinement, but with a unique, repulsive interaction between multiple excitons, which leads to long multiexciton lifetimes and a low-threshold optical gain. The same exciton-exciton repulsion decouples each CdSe facet into quasi-independent single-photon emitters, suggesting their potential for nonclassical light generation. Overall, by offering a combination of structural rigidity, ordered self-assembly, and optimized multiexciton properties, the quantum cube geometry provides a scalable platform for electrically driven light sources, gain media, and quantum photonic devices.« less

Electrocatalytic CO2 reduction often suffers from competition with the hydrogen evolution reaction (HER), which lowers efficiency and limits product selectivity. Recent studies suggest that electron spin, when controlled at an electrode surface, can influence reaction pathways, but direct evidence linking spin effects to suppressed HER has been limited. Here we show that helical chiral copper (Cu) electrodes reduce competing HER during CO2 reduction, consistent with spin polarization induced via the chiral-induced spin selectivity effect. The helically structured Cu electrodes are fabricated by electrodeposition with a chiral templating reagent. Time-resolved Kerr ellipticity measurements, which track spin-polarized carriers generated by an ultrafastmore » Seebeck current, confirm spin accumulation at the chiral Cu surface. This spin polarization disfavours H-H bond formation, thereby suppressing HER and enabling formate production alongside CO. These findings demonstrate that chirality-based spin control offers a strategy for steering selectivity in CO2 reduction and other reactions where HER is an undesired competitor.« less

Tin(II)-based hybrid halide perovskites typically suffer from severe self-doping behavior as a result of facile oxidation of Sn(II) to Sn(IV), leading to high carrier densities (holes) and metallic-like conductivities that limit their applications. In this contribution, we describe how substituting the large ethylenediammonium cation for methylammonium in the intentionally defective “hollow” perovskite family, MA_1−xen_xSn_1−0.7xI_3−0.4x (MA = methylammonium, en = ethylenediammonium), where 0 ≤ x ≤ 0.38, effectively minimizes the intrinsic self-doping behavior. The use of a solvent-free, mechanochemical synthesis route further circumvents oxidative side reactions typical in solution processing, enabling more precise control and understanding of both composition and defectmore » chemistry. Dark and time-resolved microwave conductivity measurements of these materials as a function of “x” reveal two regimes of conductivity suppression: at low x incorporation (x ≤ 0.15), the carrier density decreases by an order of magnitude via defect-mediated charge compensation, while higher substitution (0.15 < x ≤ 0.38) greatly reduces the carrier mobility. At these lower substitution levels, the observations suggest that intrinsic equilibrium tin vacancies are compensated instead by ionic defects in lieu of mobile holes. For the higher substitution levels, the less mobile carriers exhibit long recombination lifetimes, consistent with polaron-mediated transport. These findings establish a strategy for relatively low iodine chemical potential synthesis and defect-driven control of the carrier concentration in tin halide perovskites, advancing the rational discovery of dopable hybrid semiconductors.« less

Vapor-assisted hybrid two-step deposition, which combines thermally evaporated inorganic layers with solution-processed organic halides to form halide perovskites, has emerged as a scalable and industry-compatible route for textured tandem photovoltaics. However, this process is often hindered by reaction-limited phase formation, particularly when compact, non-porous, and highly crystalline inorganic layers formed by thermal evaporation restrict subsequent conversion, resulting in incomplete reaction and pronounced depth-dependent heterogeneity. In this study, we introduce a strategy to regulate the inorganic precursor layer by incorporating localized heterogeneous nucleation sites. Sparsely distributed hydrophilic metal oxide species serve as effective nucleation centers during vapor deposition, enabling effective controlmore » over film morphology and crystal orientation from the early stages of growth. This tailored inorganic framework facilitates the subsequent incorporation of organic halides, alleviating reaction limitations and suppressing residual unreacted precursors. Consequently, the perovskite films exhibit improved stoichiometric uniformity and enhanced optoelectronic quality, enabling wide-bandgap perovskite solar cells with markedly improved performance and operational stability. This work provides important mechanistic insight into crystal growth engineering of vapor-deposited perovskite thin films.« less

By blending a naphthalene diimide polymer into C₆₀, we made a solution-processed electron-transport layer (ETL) for perovskite solar cells with fracture energies of 1.25 J m⁻², over 3× higher than that of thermally evaporated C₆₀. Fracture energies were measured in a double cantilever beam configuration, and fracture surface images showed a fracture location near the ETL/perovskite interface, indicating a toughening of the interface between the ETL and Ag. We show that this modification to the ETL has no adverse effect on solar cell performance, and highlight the additional benefit of reduced parasitic absorption; a finding relevant for tandem solar cells.

The sluggish kinetics and poor stability of the oxygen reduction reaction (ORR) remain the primary bottleneck for achieving high performance in protonic ceramic fuel cells (PCFCs) at intermediate temperatures (400–650°C). In this work, a Pr-based nanocomposite cathode comprised of simple perovskite phase (PrNi_0.7Co_0.3O_3-δ) and Ruddlesden-Popper phase (Co-doped Pr₄Ni₃O_10+δ) is developed. Although PrNi_0.7Co_0.3O_3-δ solely stands as a good cathode with facile proton transfer, combining the superior catalytic activity against oxygen on the Ruddlesden-Popper phase boosts the ORR performance further. The designed nanocomposite cathode outperforms the simple perovskite cathode, attributed to enhanced oxygen absorption and surface diffusion with the Ruddlesden-Popper phase. Amore » precursor-based cathode deposition technique is also developed to achieve cathode grain sizes of ∼100 nm. A single cell with the nanocomposite cathode delivers a peak power density of 1.38 W cm⁻² at 650°C, among the highest in reported PCFCs with Pr-based cathodes, with a small degradation rate of 0.145 mV h⁻¹ during 250 h stability test. Further investigation of cathode-electrolyte interface revealed interfacial PrO₂ phase formation, promoted by abundant Pr₆O₁₁ in the nanocomposite precursor powder, thereby improving both ohmic resistance and stability. These findings highlight the effectiveness of the nanocomposite cathode and underscore its advantages on interfacial properties.« less

Nickel oxide (NiO_x) is among the few p-type metal oxide semiconductors considered a strong candidate for hole transport layers in halide perovskite solar cells (PSCs). However, its reactivity with perovskite ions poses significant challenges to achieving high efficiency and long-term stability. Here, we investigate passivation of detrimental reactive surface sites on NiO_x by carbazole phosphonic acids. We leverage electrochemical cyclic voltammetry (CV) of NiO_x electrodes as a proxy measure for the redox activity that afflicts PSCs. From the CVs, we derive a metric, N (units cm⁻²), that relates to the number of redox active sites on NiO_x surfaces. We observemore » a statistically significant negative correlation between PSC efficiency and N-value that indicates PSCs are more efficient on NiO_x with lower electrochemical reactivity. The new mechanistic insight into NiO_x passivation demonstrates it requires a reducing agent and Brønsted acid combination, providing a broadly applicable approach for evaluating and enhancing the stability and performance of NiO_x-based interfaces in photovoltaics.« less

The vast variety of nuclear security applications require radiation detection materials tailored to their operational needs. A scintillator’s properties are strongly influenced by the choice of luminescent dopant, which facilitates customization to different applications. In this work, transparent Ø12 mm single crystals of undoped CsCaCl₃, CsCaCl₃:1% Eu, CsCaCl₃:1% Tl, and CsCaCl₃:1% Eu, 1% Tl were grown via the Vertical Bridgman method. Their scintillation properties and fast neutron-gamma discrimination capabilities were investigated. Undoped CsCaCl₃ had a light yield of 2,500 ph/MeV, which is the highest reported to date for this CVL material. The incorporation of Eu²⁺ or Tl⁺ into CsCaCl₃ asmore » luminescence centers resulted in significantly higher light yields of ∼16,000 ph/MeV and energy resolutions of ∼8% at 662 keV. Compared to the single dopant counterparts, CsCaCl₃:Eu, Tl had significantly suppressed afterglow; however, this came at the cost of reduced light yield. Among the materials tested, only CsCaCl₃:Tl showed effective fast neutron and gamma discrimination capabilities, achieving a Figure of Merit of 3.2 between gamma-rays and fast neutron captures that produce protons and 1.6 between gamma-rays and fast neutron captures that produce alpha particles.« less

Achieving operational stability in halide perovskite solar cells remains a critical challenge for commercialization. Ionic liquids are promising bulk modifiers, yet their mechanistic role in perovskite crystallization is poorly understood. Here we engineered an ionic liquid, methoxyethoxymethyl-1-methylimidazole chloride (MEM-MIM-Cl), with an ethylene glycol ether side chain that regulates perovskite growth and stabilizes buried interfaces via synergistic interactions with NiO_x. MEM-MIM-Cl induces a novel intermediate phase through chelation with undercoordinated Pb(II), suppressing defects and defect-induced degradation. Solar cells incorporating MEM-MIM-Cl achieved a power conversion efficiency of 25.9% and retained 90% of their initial performance after 1,500 h under continuous 1-sun illuminationmore » and 90 °C thermal stress—surpassing prior benchmarks under milder ageing conditions. Furthermore, diurnal cyclic ageing revealed unprecedented fatigue resistance, highlighting the dual role of MEM-MIM-Cl in simultaneously enhancing efficiency and operational resilience. In conclusion, this work elucidates design principles for functional ionic liquids while advancing perovskite photovoltaics towards industrial viability.« less

As the demand for low-cost, high-efficiency solar energy technologies grows, metal halide perovskite (MHP) solar cells have emerged as a promising candidate for next-generation photovoltaics due to their high power conversion efficiencies. However, their poor durability and issues with manufacturing consistency remain significant barriers to commercialization. In this work, we develop deep learning models to support materials characterization and provide insight into features and processes influencing performance. The models are trained using transfer learning of a pretrained model to predict relevant current-voltage (IV) metrics based on different combinations of input electroluminescence (EL) and photoluminescence (PL) images of MHP devices. Wemore » examine which image types are most informative in accurately predicting different IV metrics. Additionally, we use explainable artificial intelligence (XAI) techniques to provide insights into specific spatial features in the devices that drive differences in performance. We find that stabilized luminescence images (e.g. those collected after biasing the devices for at least 1 min) are better for predicting metrics of open-circuit voltage (by PL) and short-circuit current (by PL with EL), but that predicting fill factor and overall power output may use the time-evolution of EL images. Based on attribution masks generated by integrated gradients for each device performance metric, we further suggest different loss mechanisms associated with categories of large and small spatial defects. Overall, this case study highlights the potential applicability of XAI methodology for streamlining MHP device analysis and accelerating detailed understanding of the relationships between spatial defects and impacts on performance.« less