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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]

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]

Due to the fast dynamics and re‐equilibration of supramolecular self‐assembly, bottom‐up molecular strategies to fabricate well‐defined and controllable multiblock structures are rare. Herein, we propose a new concept for fabrication of fluorescent multiblock microcolumns containing 1 to 7 blocks via hierarchical supramolecular self‐assembly based on cucurbit[8]uril (CB[8]), NaBr and an AIEgen guest. Through the complexation between CB[8] and different numbers of AIEgen guests (2, 1, 0), the competitive displacement caused by the binding of the sodium cation to the CB[8] portal, and the reversible assembly of positively charged guests in salt solutions, one‐pot hierarchical supramolecular self‐assembly is realized. The molecular structure of each block is analyzed by single‐crystal X‐ray diffraction. The AIEgen enables the self‐assembly of multiblocks to be visualized, understood, and regulated. [ABSTRACT FROM AUTHOR]

Central π‐core engineering of non‐fullerene small molecule acceptors (NF‐SMAs) is effective in boosting the performance of organic solar cells (OSCs). Especially, selenium (Se) functionalization of NF‐SMAs is considered a promising strategy but the structure‐performance relationship remains unclear. Here, we synthesize two isomeric alkylphenyl‐substituted selenopheno[3,2‐b]thiophene‐based NF‐SMAs named mPh4F‐TS and mPh4F‐ST with different substitution positions, and contrast them with the thieno[3,2‐b]thiophene‐based analogue, mPh4F‐TT. When placing Se atoms at the outer positions of the π‐core, mPh4F‐TS shows the most red‐shifted absorption and compact molecular stacking. The PM6 : mPh4F‐TS devices exhibit excellent absorption, high charge carrier mobility, and reduced energy loss. Consequently, PM6 : mPh4F‐TS achieves more balanced photovoltaic parameters and yields an efficiency of 18.05 %, which highlights that precisely manipulating selenium functionalization is a practicable way toward high‐efficiency OSCs. [ABSTRACT FROM AUTHOR]

Low‐dimensional copper halides having nontoxic elements are attracting increasing attention for their peculiar emission properties. Self‐trapped excitons (STEs) account for their high photoluminescence quantum yields (PLQYs) with emission that can stretch across the entire visible spectrum. However, intrinsic factors that influence the formation or loss of the emissive species in low‐dimensional copper halides remain elusive. Here, a comprehensive study on the STE formation dynamics of one‐dimensional CsCu2I3 and zero‐dimensional Cs3Cu2I5 is presented. It is found from STE kinetic analysis that a slower STE formation demonstrated by the 1D structure is not hindered by a potential barrier, but instead related to the number of phonons released in the self‐trapping process. It is further revealed that in 1D CsCu2I3, the non‐radiative recombination of STEs mainly occurs via the intersection between the STE state and the ground state in the configuration coordinate diagram, placing an intrinsic limit on the PLQY at room temperature. These findings show that the STE formation is affected by both the self‐trapping depth and the phonon energy as opposed to a potential barrier in low‐dimensional copper halides. The better understanding of STE formation and recombination processes provide basis for improving design and performance for broadband light emitting devices. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are known to be sensitive to the exposure to ambient humidity, which typically results in the degradation and deterioration of performance, although positive effects of exposure to moisture have also been reported, due to recrystallization of the perovskite. Common approach to improve stability is to use 3D/2D perovskite active layer, where 2D capping layer is prepared by spin coating the bulky organic cation halide. Herein, it is shown that optimizing the exposure of the capping layer prepared by spin coating phenylethylammonium iodide (PEAI) to ambient atmosphere results in substantial improvement of the PSC performance. Furthermore, the initial effects of PEAI treatment are dependent on the NiOx/perovskite interface, but in all cases except at very high humidity (80–85% RH) optimized exposure to ambient results in improved performance. The variations in device performance with PEAI treatment and ambient exposure can be attributed to defect passivation and changes in the charge extraction due to energy‐level alignment at the interfaces. The best performing devices have passivation of NiOx/perovskite interface and PEAI treatment of top surface followed by exposure to ambient atmosphere at RH of 40–45%, which results in the power conversion efficiency increase from 20.3% to 22.4%. [ABSTRACT FROM AUTHOR]

Nonfullerene organic photovoltaics (OPVs) with small energetic offset between donor and acceptor can provide a much‐reduced voltage loss and power conversion efficiencies over 18%, challenging the previous understanding of the charge generation mechanisms. Herein, a study is presented on nonfullerene OPVs with negative energetic offsets, by investigating a model system which exhibits poor photoluminescence quenching (PLQ, ≈17%) yet reasonably high external quantum efficiency (EQE, ≈50%). It is found that the discrepancy between the poor PLQ and relatively high EQE is dependent on the measurement conditions, namely, short or open circuit, under which the devices exhibit differences in charge generation. Transient absorption spectroscopy shows surprisingly slow hole transfer on nanosecond timescale. It is revealed that the poor PLQ/high radiative recombination originates from an increased back transfer from free carriers to the singlet excitons under open circuit. It is made possible by the slow charge‐transfer (CT) kinetics, long‐lived CT states, and emissive excitons. Despite the negative offset, the charge generation can be relatively efficient under short circuit. The results suggest that the PLQ under open circuit is not necessarily a good indicator of charge separation efficiency and provide new insight to efficient charge generation of OPVs with unfavorable energy offsets. [ABSTRACT FROM AUTHOR]

Electron donors and acceptors in organic solar cells (OSCs) shall strike a favorable vertical phase separation that acceptors and donors have sufficient contact and gradient accumulation near the cathodes and anodes, respectively. Random mixing of donors/acceptors at surface will result in charge accumulation and severe recombination for low carrier‐mobility organic materials. However, it is challenging to tune the vertical distribution in bulk‐heterojunction films as they are usually made from a well‐mixed donor/acceptor solution. Here, for the first time, it presents with solid evidence that the commonly used 1‐chloronaphthalene (CN) additive can tune the donor/acceptor vertical distribution and establish the mechanism. Different from the previous understanding that ascribed the efficiency enhancement brought by CN to the improved molecular stacking/crystallization, it is revealed that the induced vertical distribution is the dominant factor leading to the significantly increased performance. Importantly, the vertical distribution tunability is effective in various hot nonfullerene OSC systems and creates more channels for the collection of dissociated carriers at corresponding organic/electrode interfaces, which contributes the high efficiency of 18.29%. This study of the material vertical distribution and its correlation with molecular stacking offers methods for additives selection and provides insights for the understanding and construction of high‐performance OSCs. [ABSTRACT FROM AUTHOR]

Selective laser melting is an additive manufacturing technique that can be used to achieve excellent forming of Cu alloys. Specifically, high‐Sn–Cu alloys (e.g., Cu–10Sn) offer good wear and corrosion resistance, and are extensively used in industrial applications. Although P is considered a beneficial element in Cu–Sn alloys, particularly with respect to ductility, P‐doped Cu–10Sn alloy (Cu–10Sn–0.4P) has not yet been investigated in detail. Thus, herein, it provides valuable insights regarding the printability, residual stress level, heat treatment conditions, mechanical properties, and microstructural features of selective laser melted Cu–10Sn–0.4P. The alloy is successfully printed using a relatively wide range of processing parameters. The high levels of residual stress after printing were relieved using heat treatment under appropriate conditions. Consequently, a good combination of strength, ductility, and hardness was achieved. The addition of P led to an improved oxygen scavenging capability, thus Cu–10Sn–0.4P alloy exhibited a better ductility than P‐free Cu–Sn alloy. The excellent printability of Cu–10Sn–0.4P is demonstrated by printing a variety of objects, including flanges, sheathings, and jewelry rings. [ABSTRACT FROM AUTHOR]

Transient optical spectroscopy is used to quantify the temperature‐dependence of charge separation and recombination dynamics in P3TEA:SF‐PDI2 and PM6:Y6, two non‐fullerene organic photovoltaic (OPV) systems with a negligible driving force and high photocurrent quantum yields. By tracking the intensity of the transient electroabsorption response that arises upon interfacial charge separation in P3TEA:SF‐PDI2, a free charge generation rate constant of ≈2.4 × 1010 s−1 is observed at room temperature, with an average energy of ≈230 meV stored between the interfacial charge pairs. Thermally activated charge separation is also observed in PM6:Y6, and a faster charge separation rate of ≈5.5 × 1010 s−1 is estimated at room temperature, which is consistent with the higher device efficiency. When both blends are cooled down to cryogenic temperature, the reduced charge separation rate leads to increasing charge recombination either directly at the donor‐acceptor interface or via the emissive singlet exciton state. A kinetic model is used to rationalize the results, showing that although photogenerated charges have to overcome a significant Coulomb potential to generate free carriers, OPV blends can achieve high photocurrent generation yields given that the thermal dissociation rate of charges outcompetes the recombination rate. [ABSTRACT FROM AUTHOR]

The performance of quasi‐2D perovskite light emitting diodes (LEDs) with mixed small cations, cesium and formamidinium (FA), is significantly affected by their ratio. The best devices obtained for Cs:FA ratio of 1:1 exhibit a maximum external quantum efficiency (EQE) of 12.1%, maximum luminance of 15 070 cd m−2 and maximum current efficiency of 46.1 cd A−1, which is significantly higher (about 3 times) compared to devices with FA only (maximum EQE of 4.1%, maximum luminance of 4521 cd m−2) and Cs‐only (maximum EQE of 4.0%, maximum luminance of 4886 cd m−2). The photoluminescence quantum yield of the Cs:FA 1:1 sample is similarly enhanced, 21.3% compared 5.4% and 6%, for FA‐only and Cs‐only samples, respectively. It can be observed that the Cs:FA ratio significantly affects the crystallization of the perovskite, with the optimal 1:1 ratio resulting in the formation of tetragonal Cs0.5FA0.5PbBr3 phase (different from cubic FAPbBr3 and orthorhombic CsPbBr3) with pronounced preferential orientation as well as a significant reduction in the trap density, which leads to a substantial improvement in the light‐emitting performance. [ABSTRACT FROM AUTHOR]

Ternary copper halides have garnered significant interest for their bright, high quantum yield emission stemming from the radiative decay of self‐trapped excitons (STEs). Cesium copper halides have shown promise for use in optoelectronics, including light‐emitting devices (LEDs) for lighting and displays. To date several synthetic procedures for Cs3Cu2X5 (X = Cl, Br, and mixed Br/Cl) have been proposed for making nanocrystals, microcrystals, or polycrystalline thin films. Here, a synthetic method for making large single crystals (SCs) with millimeter dimensions in less than 30 min is presented. Phase pure mixed halide SCs are also produced and in‐depth structural analysis has been performed for the first time, definitively showing the site preferences for mixing chloride into the pure Cs3Cu2Br5 structure. Quantum yields for SCs of X = Cl and Br are 100% and 27% respectively, with long lifetimes and strong evidence of STE emission. This synthesis can be used to produce white light UV‐downconversion LEDs using ternary copper halides as the blue and green components along with the commercial red phosphor K2SiF6:Mn4+. These devices give a Commission Internationale de l'Éclairage (CIE) coordinate of (0.3327, 0.3342) and color rendering index of 90% at a color temperature of ≈5500 K. [ABSTRACT FROM AUTHOR]

The electroluminescence efficiency of perovskite light‐emitting diodes (PeLEDs) has gained notable achievements, but the poor stability under electric stress severely impedes future practical use. Here, an alkyldiammonium 1,4‐butanediamine (BDA) is incorporated into perovskite emitting layer, which substantially optimizes electrochemical stability and minimizes interfacial deep traps under large external bias. The BDA‐PeLED shows a record operational half‐lifetime T50 of 189.4 h at a high current density of 100 mA cm−2 and 681 h under 50 mA cm−2. Additionally, the device maintains its original performance upon 2500 cycles of voltage scan and withstands 10 000 times of ON–OFF under a pulsed voltage of 2.5 V. Further degradation mechanism study reveals that the main origins of the instability property of PeLEDs without BDA are the generation of deep traps at the interfaces and the infiltration of anions into adjacent layers under long‐term electric stress. The significantly enhanced electrochemical stability suggests that alkyldiammonium cation incorporation can provide a direction to solve the instability issue of PeLEDs. [ABSTRACT FROM AUTHOR]

Chemical modifications of non‐fullerene acceptors (NFAs) play vital roles in the development of high efficiency organic solar cells (OSCs). In this work, on the basis of the previously reported molecule named Y6‐1O, chlorination and inner side‐chain engineering are adopted to endow the corresponding devices with higher open‐circuit voltage (VOC) and short‐circuit current density (JSC) as well as good morphology for high fill factor (FF). As a result, the molecule named BTP1O‐4Cl‐C12 can help achieve a higher power conversion efficiency (PCE) of 17.1% than that of Y6‐1O (16.1%). Furthermore, the following comparisons between BTP1O‐4Cl‐C12 and the two symmetric acceptors named BTP2O‐4Cl‐C12 and BTP‐4Cl‐C12 demonstrate the effect of asymmetric alkoxy substitution on the outer side chains, which not only achieves a balance between VOC and JSC, but also help obtain appropriate morphology for efficient charge dissociation and suppressed charge recombination. Therefore, the asymmetric BTP1O‐4Cl‐C12 can achieve a higher PCE compared to the symmetric BTP2O‐4Cl‐C12 and BTP‐4Cl‐C12. The work not only reports an excellent NFA for high‐performance OSCs, but also puts forward a series of methods for consecutive chemical modifications on Y‐series acceptors, which can be further applied to boost the PCE of OSCs to a higher level. [ABSTRACT FROM AUTHOR]

A solution‐processed top electrode is critical to unlock the full potential of all‐solution‐processed organic solar cells (OSCs) for practical applications. However, the enabled devices suffer from low efficiency (<12%) mainly because of the irreversible damages induced by the top‐electrode deposition process. Herein, a strategy of dry and nonimmersive sintering is demonstrated by introducing a hydrogen‐intercalated molybdenum oxide layer to sinter isolated Ag nanoparticles into the top electrode (all from solution process) with little influences/issues on underlying device structures. Fundamentally, it is unveiled that the intercalated hydrogen will bond with the amino group of the ligands around Ag nanoparticles, which promotes the exposed nanoparticles to merge along a certain crystal orientation (≈45°) and form a conductive electrode (8.6 Ω sq−1). Importantly, the sintered electrode offers 70% optical reflection in the 700–1050 nm wavelength region, which is essential to enhance the light absorption of high‐performance nonfullerene acceptors. Consequently, a record efficiency of 15% is achieved, driving all‐solution processed OSCs toward commercial applications. [ABSTRACT FROM AUTHOR]

Organic solar cells based on nonfullerene acceptor molecules show high charge generation yields with negligible driving force at the donor–acceptor (D/A) interface to drive exciton dissociation. Understanding the underlying charge generation dynamics in these material systems is crucial for further development of this technology. Herein, the acceptor exciton dissociation dynamics in these materials is studied using transient optical spectroscopy. The results show that exciton dissociation at the D/A interface takes up to ≈100 ps to complete, and this process is not significantly affected by temperature. A similar timescale for charge transfer (CT) state separation into free electrons and holes is observed at room temperature. But in contrast to the weak temperature dependence of exciton dissociation, the free charge generation rate and yield are significantly reduced at low temperature. This suggests that overcoming the Coulomb barrier for charge separation at the D/A interface is the main reason for the endothermic charge separation observed for these material systems, instead of diffusion‐limited exciton dissociation. [ABSTRACT FROM AUTHOR]

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an "S‐shaped" dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions. [ABSTRACT FROM AUTHOR]

As one of the most promising hole‐transporting materials for perovskite solar cells (PSC), NiO is widely used in the inverted p–i–n cell structure due to its high stability, decent hole conductivity, and easy processability for hysteresis‐free cells. However, the efficiency of NiO‐based PSCs is still low, due largely to the poor perovskite/NiO interface. Herein, a sulfur‐doping strategy to modify NiO surface via ion exchange reaction by a simple and scalable chemical bath deposition technique is introduced, which greatly improves the photovoltaic (PV) performance of the derived devices. A systematic investigation is shown where sulfur doping leads to favorable interfacial energetics with a reduced Voc loss. Sulfur doping at the interface also improves the contact between NiO and perovksite and facilitates the formation of high‐quality perovskite films. Carrier dynamics studies demonstrate reduced defect states and trap‐assisted recombination with sulfur doping, which promote the PV performance of the devices. These merits contribute concurrently to low‐loss charge transfer across the perovskite/NiO interface and facilitate charge transport through the perovskite films, leading to a high champion efficiency of 20.43% of the p–i–n structure solar cell devices. [ABSTRACT FROM AUTHOR]

The traditional design strategies for highly bright solid‐state luminescent materials rely on weakening the intermolecular π–π interactions, which may limit diversity when developing new materials. Herein, we propose a strategy of tuning the molecular packing mode by regioisomerization to regulate the solid‐state fluorescence. TBP‐e‐TPA with a molecular rotor in the end position of a planar core adopts a long‐range cofacial packing mode, which in the solid state is almost non‐emissive. By shifting molecular rotors to the bay position, the resultant TBP‐b‐TPA possesses a discrete cross packing mode, giving a quantum yield of 15.6±0.2 %. These results demonstrate the relationship between the solid‐state fluorescence efficiency and the molecule's packing mode. Thanks to the good photophysical properties, TBP‐b‐TPA nanoparticles were used for two‐photon deep brain imaging. This molecular design philosophy provides a new way of designing highly bright solid‐state fluorophores. [ABSTRACT FROM AUTHOR]

A nonuniform vertical phase distribution and thick insulating barrier can decrease the energy transfer between slices in layered perovskite solar cells (PSCs). Herein, an interlayer cross‐linked Dion–Jacobson (DJ)‐type 2D PSC with 1,4‐butanediamine (BDA) as a short‐chain insulating spacer [formula: (BDA)MAn −1PbnI3n + 1] is reported and demonstrates the vertical phase becoming uniform with enhanced exciton coupling, leading to reduced nonradiative recombination. For n = 1 pure phase perovskite, an exciton binding energy of the DJ phase (BDA)PbI4 is ≈142 meV, much smaller than ≈435 meV of Ruddlesden–Popper (RP) phase (BA)2PbI4 (n = 1) perovskite, indicative of exciton‐coupling‐induced efficient energy transfer. Therefore, the high energy emission peaks for the (BDA)MA3Pb4I13 film are not observed even in liquid nitrogen temperature (78 K), which can be distinguished from that of the (BA)2MA3Pb4I13 film. Energy transfer between 2D slices of (BDA)MA3Pb4I13 is 100 times faster than that of (BA)2MA3Pb4I13. The uniform vertical distribution and exciton coupling mitigate nonradiative energy loss and significantly improve Voc in inverted structures (PEDOT:PSS/(BDA)MA3Pb4I13/PCBM/bathocuproine/Ag) to ≈1.15 V and the control n‐butylammonium‐based device demonstrates only a Voc = ≈1 V. It is believed that the results would provide a deep understanding of exciton coupling in hybrid multicomponent quantum wells. [ABSTRACT FROM AUTHOR]

Cell staining is a fascinating research area where monitoring and visualizing different cell organelles can be done using fluorescence techniques. However, the design and synthesis of organelle‐targeting fluorophores is still a challenge for several specific organelles. Herein, a platform for synthesizing efficient red‐emitting aggregation‐induced emission luminogens (AIEgens) with donor–acceptor characteristics is reported. The core molecule can be easily functionalized in order to modulate organelle targeting. The three synthesized AIEgens exhibit quantum yields of up to 39.3% and two‐photon absorption cross‐section values of up to 162 GM. The two zwitterionic AIEgens, CDPP‐3SO3 and CDPP‐4SO3, with the sulfonate function group, are successfully utilized for specific one‐photon and two‐photon imaging of the endoplasmic reticulum (ER) in live human cells. Substituting the zwitterionic nature with a singly positive charge group, one‐photon and two‐photon imaging of CDPP‐BzBr shows mitochondrial specificity, indicating the importance of the zwitterionic group for ER‐targeting. Owing to the good in vitro photostability, cell viability, and high efficiency, these red dyes serve as a good potential candidate for specific organelle targeting, as well as illustrate how such a platform can easily aid in the study of structure–property relationships for designing such probes. [ABSTRACT FROM AUTHOR]

Ruddlesden–Popper halide perovskite (RPP) materials are of significant interest for light‐emitting devices since their emission wavelength can be controlled by tuning the number of layers n, resulting in improved spectral stability compared to mixed halide devices. However, RPP films typically contain phases with different n, and the low n phases tend to be unstable upon exposure to humidity, irradiation, and/or elevated temperature which hinders the achievement of pure blue emission from n = 2 films. In this work, two spacer cations are used to form an RPP film with mixed cation bilayer and high n = 2 phase purity, improved stability, and brighter light emission compared to a single spacer cation RPP. The stabilization of n = 2 phase is attributed to favorable formation energy, reduced strain, and reduced electron–phonon coupling compared to the RPP films with only one type of spacer cation. Using this approach, pure blue light‐emitting diodes (LEDs) with Commission Internationale de l'éclairage (CIE) coordinates of (0.156, 0.088) and excellent spectral stability are achieved. [ABSTRACT FROM AUTHOR]

Abstract: Solution‐processed and low‐temperature Sn‐rich perovskites show their low bandgap of about 1.2 eV, enabling potential applications in next‐generation cost‐effective ultraviolet (UV)–visible (vis)–near infrared (NIR) photodetection. Particularly, the crystallization (crystallinity and orientation) and film (smooth and dense film) properties of Sn‐rich perovskites are critical for efficient photodetectors, but are limitedly studied. Here, controllable crystallization for growing high‐quality films with the improvements of increased crystallinity and strengthened preferred orientation through a introducing rubidium cation into the methylammonium Sn‐Pb perovskite system (65% Sn) is achieved. Fundamentally, the theoretical results show that rubidium incorporation causes lower surface energy of (110) plane, facilitating growth in the dominating plane and suppressing growth of other competing planes. Consequently, the methylammonium‐rubidium Sn‐Pb perovskite photodetectors simultaneously achieve larger photocurrent and lower noise current. Finally, highly efficient UV–vis–NIR (300–1100 nm) photodetectors with record‐high linear dynamic range of 110 and 3 dB cut‐off frequency reaching 1 MHz are demonstrated. This work contributes to enriching the cation selection in Sn‐Pb perovskite systems and offering a promising candidate for low‐cost UV–vis–NIR photodetection. [ABSTRACT FROM AUTHOR]

Abstract: Hole transport layer (HTL) plays a critical role for achieving high performance solution‐processed optoelectronics including organic electronics. For organic solar cells (OSCs), the inverted structure has been widely adopted to achieve prolonged stability. However, there are limited studies of p‐type effective HTL on top of the organic active layer (hereafter named as top HTL) for inverted OSCs. Currently, p‐type top HTLs are mainly 2D materials, which have an intrinsic vertical conduction limitation and are too thin to function as practical HTL for large area optoelectronic applications. In the present study, a novel self‐assembled quasi‐3D nanocomposite is demonstrated as a p‐type top HTL. Remarkably, the novel HTL achieves ≈15 times enhanced conductivity and ≈16 times extended thickness compared to the 2D counterpart. By applying this novel HTL in inverted OSCs covering fullerene and non‐fullerene systems, device performance is significantly improved. The champion power conversion efficiency reaches 12.13%, which is the highest reported performance of solution processed HTL based inverted OSCs. Furthermore, the stability of OSCs is dramatically enhanced compared with conventional devices. The work contributes to not only evolving the highly stable and large scale OSCs for practical applications but also diversifying the strategies to improve device performance. [ABSTRACT FROM AUTHOR]

Abstract: The effects of alkyl chain regiochemistry on the properties of donor polymers and performances of non‐fullerene organic solar cells are investigated. Two donor polymers (PfBTAZ and PfBTAZS) are compared that have nearly identical chemical structures except for the regiochemistry of alkyl chains. The optical properties and crystallinity of two polymers are nearly identical yet the PfBTAZ:O‐IDTBR blend exhibits nearly double domain size compared to the blend based on PfBTAZS:O‐IDTBR. To reveal the origins of the very different domain size of two blends, the morphology of neat polymer films is characterized, and it is found that PfBTAZ tends to aggregate into much larger polymer fibers without the presence of O‐IDTBR. This indicates that it is not the polymer:O‐IDTBR interactions but the intrinsic aggregation properties of two polymers that determine the morphology features of neat and blend films. The stronger aggregation tendency of PfBTAZ could be explained by its more co‐planar geometry of the polymer backbone arising from the different alkyl chain regiochemistry. Combined with the similar trend observed in another set of donor polymers (PTFB‐P and PTFB‐PS), the results provide an important understanding of the structure–property relationships that could guide the development of donor polymers for non‐fullerene organic solar cells. [ABSTRACT FROM AUTHOR]

Luminogens with aggregation-induced emission characteristics (AIEgens) are intriguing due to its rapid expansion in various high-tech applications. However, there is still in high demand on the development of novel AIEgens with easy preparation and functionalization, stable structures, tunable emissions, and high quantum efficiency. In this contribution, three AIEgens based on diphenyl isoquinolinium (IQ) derivatives are reported. They can be facilely synthesized and possess high structural stability, favorable visible light excitation, large Stokes shifts, high quantum yields, tunable colors, and sufficient two-photon absorption of near-infrared light. Importantly, they exhibit multifunctionalities. They exhibit mechanochromic property, making them capable to be applied for rewritable papers. They can also be applied in mitochondrial imaging with high specificity, cell permeability, brightness, biocompatibility, and photostability. They are promising for the applications in evaluation of mitochondrial membrane potential and image-guided cancer cell ablation. Last, they are able to stain bacteria in a wash-free manner. All these intriguing results suggest such readily accessible and multifunctional diphenyl IQ-based AIEgens provide a new platform for construction of advanced materials for practical applications. [ABSTRACT FROM AUTHOR]

The mixed perovskite (FAPbI3)1− x(MAPbBr3) x, prepared by directly mixing different perovskite components, suffers from phase competition and a low-crystallinity character, resulting in instability, despite the high efficiency. In this study, a dual ion exchange (DIE) method is developed by treating as-prepared FAPbI3 with methylammonium brodide (MABr)/tert-butanol solution. The converted perovskite thin film shows an optimized absorption edge at 800 nm after reaction time control, and the high crystallinity can be preserved after MABr incorporation. More importantly, it is found that the threshold electrical field to initiate ion migration is greatly increased in DIE perovskite thin film because excess MABr on the surface can effectively heal structural defects located on grain boundaries during the ion exchange process. It contributes to the over-one-month moisture stability under ≈65% room humidity (RH) and greatly enhanced light stability for the bare perovskite film. As a result of preserved high crystallinity and simultaneous grain boundary passivation, the perovskite solar cells fabricated by the DIE method demonstrate reliable reproducibility with an average power conversion efficiency (PCE) of 17% and a maximum PCE of 18.1%, with negligible hysteresis. [ABSTRACT FROM AUTHOR]

In article number 1601882, Keyou Yan, Jianbin Xu, and co‐workers report a simple intermediate halide exchange reaction between nonstoichiometric FAI and unstable intermediate HPbI2Br to produce high‐quality FAPbI3‐xBrx thin films with crystal domain up to 2‐3 μm, eliminating the use of antisolvent dripping process. And it demonstrates outstanding opto‐electronic performances as well as enhanced stability under moisture and heat stress. [ABSTRACT FROM AUTHOR]

While indirectly patterned organic-inorganic hybrid perovskite nanostructures have been extensively studied for use in perovskite optoelectronic devices, it is still challenging to directly pattern perovskite thin films because perovskite is very sensitive to polar solvents and high-temperature environments. Here, a simple and low-cost approach is proposed to directly pattern perovskite solid-state films into periodic nanostructures. The approach is basically perovskite recrystallization through phase transformation with the presence of a periodic mold on an as-prepared solid-state perovskite film. Interestingly, this study simultaneously achieves not only periodically patterned perovskite nanostructures but also better crystallized perovskites and improved optical properties, as compared to its thin film counterpart. The improved optical properties can be attributed to the light extraction and increased spontaneous emission rate of perovskite gratings. By fabricating light-emitting diodes using the periodic perovskite nanostructure as the emission layers, approximately twofold higher radiance and lower threshold than the reference planar devices are achieved. This work opens up a new and simple way to fabricate highly crystalline and large-area perovskite periodic nanostructures for low-cost production of high-performance optoelectronic devices. [ABSTRACT FROM AUTHOR]