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Metal chalcogenide nanocrystals with variable composition and shape can conveniently be produced using cation exchange synthesis; however, the presence of cation‐containing ligands inherited from the starting material often results in contamination of the final product. To address this issue, a two‐step ligand replacement strategy is developed to fabricate CuInSe2/CuInS2 nanorods from CdSe/CdS nanorods via removal of Cd‐phosphonates from an intermediate Cu2‐xSe/Cu2‐xS phase used in the cation exchange conversion. This synthetic approach furnishes CuInSe2/CuInS2 nanorods with cadmium content below 1 at.%, and high photoluminescence quantum yields reaching 40% in the near‐infrared spectral range. Transient absorption studies reveal that the band alignment in the CuInSe2/CuInS2 heterostructure features a quasi‐type II character, with an electron localized in the core and a hole wavefunction spread over the entire nanorod. The efficient passivation of the core and the reduced Cd content leads to excitonic emission with full width at half maximum down to 110 meV, superimposed with a broad emission band from copper‐induced defects. Field‐effect transistors based on cadmium‐free CuInSe2/CuInS2 nanorods show two orders of magnitude lower noise current density compared with the cadmium‐rich devices. The responsivity and specific detectivity of these devices reach 230 mA W−1 and 108 Jones, respectively, under near‐infrared excitation at room temperature. [ABSTRACT FROM AUTHOR]

Bound states in the continuum (BICs) are widely exploited in all‐dielectric metasurfaces to significantly enhance the Q‐factor and second harmonic generation (SHG). However, a higher SHG conversion efficiency is overshadowed by the narrow transparency window of all‐dielectric materials and strict requirement of polarization‐matching. Herein, an augmented SHG assisted is demonstrated by symmetry‐protected quasi‐BICs from z‐cut wurtzite GaN metasurfaces, whose wide transparent range suppresses self‐absorption of second harmonic. Strong resonances emerge under both X‐ and Y‐polarized excitations, where the multipole characters of each eigenmode are quantitatively identified via decomposition simulations. The local field enhancement enabled by the extreme energy confinement of quasi‐BICs contributes to an efficient SHG, recording a conversion efficiency up to 2 × 10−7 at moderately low input peak intensity (≈1 GW cm−2), orders of magnitude larger than bulk GaN. With proper design, the overlapping X‐ and Y‐polarized resonances can support SHG from excitation with arbitrary polarizations. The alleviation of polarization‐matching remarkably enhances the SHG power by 66.2% under unpolarized illumination condition. The results of intense SHG reveal GaN as a promising candidate for high‐performance nanoscale nonlinear photonic devices. The weak polarization sensitivity of the designed structure will chart a novel course for the advancement of next‐generation efficient all‐dielectric metasurfaces. [ABSTRACT FROM AUTHOR]

Cyanation is a common chemical modification strategy to fine‐tune the energy levels and molecular packing of organic semiconductors, especially materials used in organic solar cells (OSCs). Generally, cyanation is used to modify the end groups of high‐performance small‐molecule acceptors (SMAs). However, the cyanation strategy has not been investigated on the central backbone of SMAs, which could introduce stronger intermolecular interaction and enhance the π–π stacking for rapid charge transport. This paper, for the first time, reports a new cyanation strategy on the central benzo‐quinoxaline core and synthesizes two novel A‐DA'D‐A type SMAs, named BQx‐CN and BQx‐2CN, with mono‐ and di‐cyanide groups, respectively. Through tailoring the number of CN groups, the BQx‐CN‐based OSC exhibits the best device performance of 18.8%, which is significantly higher than the non‐cyano BQx‐based one. The reason for the superior performance of BQx‐CN‐based devices can be attributed to the fine‐tuned energy level, stronger packing, and ideal phase segregation, which lead to superior exciton dissociation, faster charge transport, and suppressed recombination, therefore the highest fill factor (FF) and power conversion efficiencies (PCE). The research demonstrates the effectiveness of the cyanation strategy on the central core of SMAs for enhanced molecular packing and better performance of OSCs. [ABSTRACT FROM AUTHOR]

The emission peak shift caused by ion motion, especially under high bias voltage, is an obstacle to the development of blue perovskite light‐emitting diodes (PeLEDs). In this work, 3‐Aminopiperidine dihydrochloride (3AP) to construct heterocyclic dication Dion‐Jacobson (DJ) PeLEDs is introduced, and found that 3AP incorporation can retard the halide segregation and chloride loss, leading to the improvement of the emission spectral stability. By increasing the amount of 3AP (DJ phase), emission centers can be tuned from green to blue but the excitonic peak abnormally disappears, indicative of exciton delocalization. Photoluminescence quantum yield (PLQY) and ultrafast spectroscopy indicated that the introduction of 3AP can passivate defects and control the exciton delocalization to facilitate interlayer charge transfer. The external quantum efficiencies (EQE) of the obtained green (513 nm), sky blue (488 nm), and blue (478 nm) PeLEDs reached 3.0%, 7.1%, and 4.8%, respectively, and the maximum luminance is 10956, 1093 and 782 cd m−2, respectively. Most importantly, under high operating voltages from 3 to 10 V, the PeLEDs delivered outstanding spectral stability free of peak shift. [ABSTRACT FROM AUTHOR]

Despite recent advances, it is still difficult to fabricate deep blue‐emitting perovskite light‐emitting diodes (LEDs) that are immune to the color instability caused by halide mixing. This is largely because it is still challenging to achieve bright, stable, pure bromide perovskite materials with deep blue emission. Here, a novel strategy is reported for synthesizing ultrasmall CsPbBr3 quantum dots (QDs) under ambient conditions. Precise size control is used to tune the peak emission wavelengths, via the confinement effect, from 433 to 501 nm. These ultrasmall QDs, with sizes of 2–6 nm, exhibit ultralow trap density and stable photoluminescence quantum yields up to 94%, particularly in the deep blue spectral region (440–465 nm). QD‐LEDs fabricated with these materials achieve an external quantum efficiency of 1.0% at 459 nm. The exceptional control of the emission properties demonstrated here suggests a new strategy for building stable, efficient blue QD‐LEDs. [ABSTRACT FROM AUTHOR]

Organic solar cell (OSC) development continues to demonstrate impressive device efficiency improvements. However, the materials synthetic simplicity essential to industrialization remains seriously lacking attention, imparting inferior performance records in low‐cost devices. Hence, low bandgap and completely non‐fused electron acceptors (CNFEAs) having simple molecular structures are investigated herein. In contrast to typically explored fused‐ring acceptors with smaller backbone conformational variations, minimizing the interface recombination sites through a greater extent of localized domains is identified as more critical in CNFEAs, leading to remarkable fill factors (FFs) approaching 75%, among the highest currently realized for low‐cost systems. However, this comes with diminishing charge generation efficiency. The general ternary blend optimization strategy modifying the morphology of host components is limited in preserving such remarkably high FFs. To suppress the trade‐off while keeping notable FFs, a new perspective of constructing functionally bridged components based on optical, electronic, and thermodynamic properties is introduced here. Specifically, charge generation is unrestrained from the host acceptor localized domains through the introduction of a "bridge" component while also taking advantage of the configuration to channel polarons toward the efficient transport moieties of the host components. Accordingly, this work incubates understanding‐guided optimizations toward the advancement of more practical devices. [ABSTRACT FROM AUTHOR]

Hetero‐epitaxy for integration of efficient III‐V lasers on silicon can enable wafer‐scale silicon photonic integrated circuits, which can unleash the full advantages of silicon photonics in production on large silicon wafers with low cost, high throughput, and large bandwidth and large‐scale integration. In this work, efficient III‐V distributed feedback (DFB) lasers selectively grown on (001) silicon‐on‐insulator (SOI) wafers are presented. The selective hetero‐epitaxy of sufficiently large areas of III‐V segments allows the demonstration of DFB lasers on the SOI wafer. The fabricated DFB lasers feature a co‐planar configuration with the Si layer, allowing for efficient coupling between III‐V lasers and Si waveguides. The unique III‐V‐on‐insulator structure also provides strong optical confinement for the lasers. Gratings are designed and fabricated with minimal non‐radiative recombination and a simple process with good tolerance. The optically pumped DFB laser has a low lasing threshold of around 17.5 µJ cm−2, stable single‐mode lasing at 1.5 µm, a side‐mode‐suppression‐ratio of over 35 dB, and a spontaneous emission factor of 0.7. The results here demonstrate a step forward towards wafer‐scale integration with monolithically grown lasers, thus outlining the prospect of fully integrated Si photonics. [ABSTRACT FROM AUTHOR]

In order to advance the development of quantum emitter‐based devices, it is essential to enhance light‐matter interactions through coupling between semiconductor quantum dots with high quality factor resonators. Here, efficient tuning of the emission properties of HgTe quantum dots in the infrared spectral region is demonstrated by coupling them to a plasmonic metasurface that supports bound states in the continuum. The plasmonic metasurface, composed of an array of gold nanobumps, is fabricated using single‐step direct laser printing, opening up new opportunities for creating exclusive 3D plasmonic nanostructures and advanced photonic devices in the infrared region. A 12‐fold enhancement of the photoluminescence in the 900–1700 nm range is observed under optimal coupling conditions. By tuning the geometry of the plasmonic arrays, controllable shaping of the emission spectra is achieved, selectively enhancing specific wavelength ranges across the emission spectrum. The observed enhancement and shaping of the emission are attributed to the Purcell effect, as corroborated by systematic measurements of radiative lifetimes and optical simulations based on the numerical solution of Maxwell's equations. Moreover, coupling of the HgTe photoluminescence to high quality factor modes of the metasurface improves emission directivity, concentrating output within an ≈20° angle. [ABSTRACT FROM AUTHOR]

Producing efficient blue and deep blue perovskite LEDs (PeLEDs) still represents a significant challenge in optoelectronics. Blue PeLEDs still have problems relating to color, luminance, and structural and electrical stability so new materials are needed to achieve better performance. Recent reports suggest using low n states (n = 1, 2, 3) to achieve blue electroluminescence in Ruddlesden–Popper (RP) perovskite films. However, there are fewer reports on the other quasi‐2D structure, Dion–Jacobson (DJ) perovksites, despite their highly desirable optical properties, due to the difficulty in achieving charge injection. To resolve this issue, herein, w e have mixed DJ phase precursors, propane‐1,3‐diammonium (PDA) bromide into RP phase perovskites and fabricated low‐dimensional PeLEDs. It is found that these specific precursors aid in suppressing both the low n (n = 1) and high n (n ≥ 4) quasi‐2D RP phases and is an effective strategy in blue‐shifting sky‐blue RP perovskites into the sub‐470 nm region. With optimization of the PDA concentration and device layers, it is achieved an external quantum efficiency of 1.5% at 469 nm and stable electroluminescence for the first deep blue PeLED to be reported using DJ perovskites. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have emerged as promising next-generation optoelectronic materials and achieved remarkable performances in both light-emitting diodes (LEDs) and solar cells (SCs). Despite reaching market demands such as high efficiencies and low manufacturing cost, the long-term stability of MHPs is still a massive challenge for commercialization. The presence of surface and bulk defects due to low-temperature solution-processable methods causes past degradation of perovskites. Here, we have investigated the passivation strategy for methylammonium lead iodide (MAPbI3) using resin polymer poly-[(phenylglycidyl ether)-co-formaldehyde] (PCF). PCF acts as a Lewis base additive with an electron-donating oxygen atom, which can coordinate with undercoordinated Pb2+ ions or NH3+ in perovskite crystals, developing smaller nanocrystalline grains with reduced defects. As a result, the PCF-passivated samples exhibit improved stability against moisture in a humid ambient environment (RH > 70%). Moreover, enhanced photoluminescence (PL) and lifetime were achieved without encapsulation. Furthermore, LEDs are demonstrated using the optimized PCF content. These results show the importance of resin polymers, which performs multiple functionalities such as nanocrystalline grain formation, defect passivation, and stability improvements for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Although the electroluminescent performances of perovskite light‐emitting diodes (PeLEDs) are continuously improved through defect management strategies, the complicated design of passivation ligands brings great challenges to the rational defect‐annihilation process. Herein, considering the bonding strength with uncoordinated Pb2+, the methoxy group with strong electron donating ability is introduced to commonly used phenethylammonium ligand as an efficient additive, namely 4‐methoxy‐phenethylammonium iodide (4‐MeO‐PEAI), to facilitate passivation process in perovskite light‐emitting materials. It is demonstrated that the 4‐MeO‐PEAI agent substantially increases the crystal orientation, enlarges the crystalline grain size, and mitigates the deep‐level trap centers through strong bonding between the methoxy group with unpaired Pb2+ ions. The external quantum efficiencyvalue of the PeLEDs with optimized passivation reaches a maximum of 21.6%, with an emission peak of 790 nm. In addition, a nearly threefold increase of the operational half‐lifetime T50 of the 4‐MeO‐PEAI‐mediated devices is observed as compared to the reference sample. Further theoretical calculation results suggest that the adhesion of the ligands on perovskite surface via vacancies leads to an increased dissociation barrier of perovskite; thus, ameliorating the degradation of the PeLEDs under electric field. The findings provide an effective design strategy of the passivation agents to produce high‐performance perovskite‐based optoelectronics devices. [ABSTRACT FROM AUTHOR]

Chiral perovskite nanocrystals have emerged as an interesting chiral excitonic platform that combines both structural flexibility and superior optoelectronic properties. Despite several recent demonstrations of optical activity in various chiral perovskite nanocrystals, efficient circularly polarized luminescence (CPL) with tunable energies remains a challenge. The chirality imprinting mechanism as a function of perovskite nanocrystal dimensionality remains elusive. Here, atomically thin inorganic perovskite nanoplatelets (NPLs) are synthesized with precise control of layer thickness and are functionalized by chiral surface ligands, serving as a unique platform to probe the chirality transfer mechanism at the organic/perovskite interface. It is found that chirality is successfully imprinted into mono‐, bi‐, and tri‐layer inorganic perovskite NPLs, exhibiting tunable circular dichroism (CD) and CPL responses. However, chirality transfer decreases in thicker NPLs, resulting in decreased CD and CPL dissymmetry factors for thicker NPLs. Aided by large‐scale first‐principles calculations, it is proposed that chirality transfer is mainly mediated through a surface distortion rather than a hybridization of electronic states, giving rise to symmetry breaking in the perovskite lattice and spin‐split conduction bands. The findings described here provide an in‐depth understanding of chirality transfer and design principles for distorted‐surface perovskites for chiral photonic applications. [ABSTRACT FROM AUTHOR]

Tuning the properties of non‐fullerene acceptors (NFAs) through halogenation, including fluorination and chlorination, represents one of the most promising strategies to boost the performance of organic solar cells (OSCs). However, it remains unclear how the F and Cl choice influences the molecular packing and performance between small‐molecule and polymeric acceptors. Here, a series of small‐molecule and polymeric acceptors with different amounts and types of halogenation is synthesized, and the effects of fluorination and chlorination between small‐molecule and polymeric acceptors are investigated. It is found that chlorinated small‐molecule acceptors lead to longer exciton diffusion length and better performance compared to the corresponding fluorinated ones, which attributes to their stronger intermolecular packing mode. For polymer acceptors, in contrast, the fluorinated polymers achieve a denser packing mode and better performance, because chlorinated polymers exhibit reduced intrachain conjugation between end group moieties and linker units. This study demonstrates different halogenation effects on the packing modes and performances for small‐molecule and polymeric acceptors, which provides important guidance for the molecule design of high‐performance acceptors for OSCs. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSC) feature a hierarchical structure with the electron donor/acceptor layer sandwiched by anode and cathode, which raises the importance of controlling the molecular crystal orientation, domain size, and vertical distribution to facilitate the charge collection at electrodes. However, the similar conjugated backbone of donor/acceptor material and fast film‐formation kinetics have led to spinodal‐decomposition‐orientated phase separation that result in the film presenting an intimately mixed morphology and random molecular orientation. To solve the issue, the mixing Gibbs free energy‐triggered solid–liquid phase separation during the film formation process is enhanced by solidifying one component and solvating the other based on a liquid additive. Following the liquid evaporation process, a favorable vertical distribution is obtained. Meanwhile, the prolonged solvation process enlarges the domain size and assists the molecules to diffuse and orient properly, enabling better exciton/charge dynamics during the power conversion processes. As a result, the fabricated devices exhibit a fill factor over 80% and an efficiency of 18.72%, which is one of the top efficiencies for binary OSCs. Insights and a methodology is provided here to manipulate the organic donor/acceptor phase separation in terms of mixing Gibbs free energy. [ABSTRACT FROM AUTHOR]

Laser processing of pure Cu is often challenging because of Cu's very low absorptivity to most laser beams, and this difficulty is applicable to the recently developed laser powder bed fusion (LPBF) additive manufacturing (AM). How to realize high‐quality LPBF forming is urgently pursued to maximize its advanced manufacturing potential in directly making various Cu parts. Herein, two approaches have been applied, individually or simultaneously, to address the poor printability problem of the pure Cu: one is to conduct intentional oxidation treatment to the pure Cu powder to vary its surface structure and then enhance its laser absorptivity; and the other is to adopt laser remelting to counter its high thermal conductivity and provide extra liquid phase for better densification. Various research means were used to investigate mechanical performances, microstructural details, and electrical performance of the as‐printed Cu. Results show that a maximum relative density of ≈99.0% can be realized by using the two approaches simultaneously, while oxidation temperature and remelting times are the two important factors to be considered. The methodology developed in this study is expected to be applicable to other highly reflective materials as well. [ABSTRACT FROM AUTHOR]

Tin-based halide perovskite materials are of interest for light-emitting applications due to their broad yellow emission, but they are known to exhibit inferior stability compared to lead-based perovskites due to the tendency of Sn2+ to be readily oxidized. Here, we investigated the ambient stability of a Dion–Jacobson tin bromide perovskite. We found that the optical properties of the samples were more significantly affected by moisture rather than the ratio of Sn2+/Sn4+. The exposure to humidity resulted in changes in the ratio of 2D HDASnBr4 and hydrated 1D HDA3SnBr8 phases (where HDA denotes hexane-1,6-diammonium), with an initial increase (up to ∼40 h) in luminescence attributed to the increasing fraction of the hydrated 1D phase which contributes to self-trapped exciton emission. With further exposure to humidity, the material starts to degrade resulting in reduced luminescence after ∼40 h. The use of additives for the suppression of oxidation of Sn2+, namely SnCl2 and tetraethyl orthosilicate (TEOS), results in prolonging the lifetime of the samples (>260 h for thin films with additives, compared to 180 h for thin films without additives). However, the persistence of luminescence with an increased time of ambient exposure in samples prepared with additives can be attributed to the changes in the evolution of phase compositions (ratios of 2D and hydrated 1D phases) over time rather than suppression of the oxidation of Sn2+. [ABSTRACT FROM AUTHOR]