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Perovskite solar cells have emerged as a potential competitor to the silicon photovoltaic technology. The most representative perovskite cells employ SnO2 and spiro‐OMeTAD as the charge‐transport materials. Despite their high efficiencies, perovskite cells with such a configuration show unsatisfactory lifespan, normally attributed to the instability of perovskites and spiro‐OMeTAD. Limited attention was paid to the influence of SnO2, an inorganic material, on device stability. Here we show that improving SnO2 with a redox interfacial modifier, cobalt hexammine sulfamate, simultaneously enhances the power‐conversion efficiency (PCE) and stability of the perovskite solar cells. Redox reactions between the bivalent cobalt complexes and oxygen lead to the formation of a graded distribution of trivalent and bivalent cobalt complexes across the surface and bulk regions of the SnO2. The trivalent cobalt complex at the top surface of SnO2 raises the concentration of (SO3NH2)− which passivates uncoordinated Pb2+ and relieves tensile stress, facilitating the formation of perovskite with improved crystallinity. Our approach enables perovskite cells with PCEs of up to 24.91 %. The devices retained 93.8 % of their initial PCEs after 1000 hours of continuous operation under maximum power point tracking. These findings showcase the potential of cobalt complexes as redox interfacial modifiers for high‐performance perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

The demand for high‐performance X‐ray detectors leads to material innovation for efficient photoelectric conversion and carrier transfer. However, current X‐ray detectors are often susceptible to chemical and irradiation instability, complex fabrication processes, hazardous components, and difficult compatibility. Here, we investigate a two‐dimensional (2D) material with a relatively low atomic number, Ti3C2Tx MXenes, and single crystal silicon for X‐ray detection and single‐pixel imaging (SPI). We fabricate a Ti3C2Tx MXene/Si X‐ray detector demonstrating remarkable optoelectronic performance. This detector exhibits a sensitivity of 1.2 × 107 μC Gyair−1 cm−2, a fast response speed with a rise time of 31 μs, and an incredibly low detection limit of 2.85 nGyair s−1. These superior performances are attributed to the unique charge coupling behavior under X‐ray irradiation via intrinsic polaron formation. The device remains stable even after 50 continuous hours of high‐dose X‐ray irradiation. Our device fabrication process is compatible with silicon‐based semiconductor technology. Our work suggests new directions for eco‐friendly X‐ray detectors and low‐radiation imaging system. [ABSTRACT FROM AUTHOR]

Wavelength conversion based on hybrid inorganic–organic sensitized triplet–triplet annihilation upconversion (TTA‐UC) is promising for applications such as photovoltaics, light‐emitting‐diodes, photocatalysis, additive manufacturing, and bioimaging. The efficiency of TTA‐UC depends on the population of triplet excitons involved in triplet energy transfer (TET), the driving force in TET, and the coupling strength between the donor and acceptor. Consequently, achieving highly efficient TTA‐UC necessitates the precise control of the electronic states of inorganic donors. However, conventional covalently bonded nanocrystals (NCs) face significant challenges in this regard. Herein, a novel strategy to exert control over electronic states is proposed, thereby enhancing TET and TTA‐UC by incorporating ionic‐bonded CsPbBr3 and lanthanide Ce3+ ions into composite NCs. These composite‐NCs exhibit high photoluminescence quantum yield, extended single‐exciton lifetime, quantum confinement, and uplifted energy levels. This engineering strategy of electronic states engendered a comprehensive impact, augmenting the population of triplet excitons participating in the TET process, enhancing coupling strength and the driving force, ultimately leading to an unconventional, dopant concentration‐dependent nonlinear enhancement of UC efficiency. This work not only advances fundamental understanding of hybrid TTA‐UC but also opens a door for the creation of other ionic‐bonded composite NCs with tunable functionalities, promising innovations for next‐generation optoelectronic applications. [ABSTRACT FROM AUTHOR]

Perovskite nanocrystals (PeNCs) deliver size‐ and composition‐tunable luminescence of high efficiency and color purity in the visible range. However, attaining efficient electroluminescence (EL) in the near‐infrared (NIR) region from PeNCs is challenging, limiting their potential applications. Here we demonstrate a highly efficient NIR light‐emitting diode (LED) by doping ytterbium ions into a PeNCs host (Yb3+ : PeNCs), extending the EL wavelengths toward 1000 nm, which is achieved through a direct sensitization of Yb3+ ions by the PeNC host. Efficient quantum‐cutting processes enable high photoluminescence quantum yields (PLQYs) of up to 126 % from the Yb3+ : PeNCs. Through halide‐composition engineering and surface passivation to improve both PLQY and charge‐transport balance, we demonstrate an efficient NIR LED with a peak external quantum efficiency of 7.7 % at a central wavelength of 990 nm, representing the most efficient perovskite‐based LEDs with emission wavelengths beyond 850 nm. [ABSTRACT FROM AUTHOR]

A distinct advantage of halide perovskite semiconductors is their potential as gain media in high‐performance, all‐solution‐processed flexible lasers. However, most perovskite microlasers employ external optical resonators with rigid and high‐temperature/vaccum‐processed structures unsuitable for flexible applications. Here, low‐threshold, external‐cavity‐free perovskite lasers (≈550 nm, linewidth: ≈0.3 nm, quality factor: ≈1900, room temperature), prepared with excellent reproducibility using simple one‐step spin‐coating and low‐temperature annealing, are demonstrated. Exceptionally low lasing thresholds of 9.3 and 14.6 µJ cm−2 are achieved for external‐cavity‐free perovskite lasers on rigid and flexible substrates, respectively. The thresholds and quality factors are on par with that of high‐performance perovskite microlasers with well‐designed external cavities. The lasers exhibit good operational stability, showing half‐life of >1.8 × 108 pulses under optical pumping in air. Transient optical experiments reveal that the low thresholds stem from enhanced band‐to‐band spontaneous and stimulated emission processes in the high‐quality microcrystalline perovskite, effectively out‐pacing trap‐mediated and Auger processes detrimental to the lasing action. The flexible perovskite lasers retain >95% of the initial intensity after 10000 bending cycles, showing outstanding mechanical durability. As these lasers can be produced from solution within minutes at low costs, the findings are expected to enable high‐throughput, scalable fabrication of perovskite lasers for emerging applications. [ABSTRACT FROM AUTHOR]

Quasi‐2D perovskites show great promise for light‐emitting diodes owing to suppressed non‐radiative losses enabled by the energy funneling/cascading nanostructures. However, for red emission quasi‐2D perovskites, these ideal energy landscapes for efficient perovskite light‐emitting diodes (PeLEDs) can rarely be achieved due to detrimental aggregation of the low‐dimensional ligands in perovskite precursors, leading to poor device efficiency and stability. Here, a ligand‐modulated dimensionality control strategy is explored to achieve uniform phase distribution and reduce defect density for efficient light emission. In contrast to the model phenethylammonium iodide 2D ligand, the formation of small‐n phases can be inhibited by a structurally similar phenoxyethylammonium iodide ligand owing to the weakened aromatic stacking between ligands. Besides, the oxygen atoms can interact with the uncoordinated Pb2+ ions and promote the NI coordination in the perovskites, which greatly reduces the non‐radiative recombination defects in the ionic lattice. With this simple and effective approach, deep‐red quasi‐2D PeLEDs with record‐high external quantum efficiency of 21.6% and decent operational stability are achieved without the need for additional additives. These results highlight the potential of ligand‐modulated dimensionality control to achieve highly efficient and stable PeLEDs with a facile fabrication process. [ABSTRACT FROM AUTHOR]

A silicon‐integrated MXene X‐ray detector exhibits high sensitivity and an ultra‐low detection limit, enabling clear and precise single‐pixel X‐ray imaging [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) are a promising class of materials for next‐generation display and lighting applications. Since the first demonstration of bright electroluminescence (EL) from perovskite light‐emitting diodes (PeLEDs) in 2014, the EQEs of these devices increased from below 1% to more than 20% in merely four years. Despite the meteoritic rise of device efficiencies that placed the new LED technology in the spotlight, many scientific and technical challenges remain, preventing PeLEDs from advancing further into practical applications. The success of inorganic III‐V LEDs, or commercial LED technologies in general, lies in the ability to demonstrate the reliable generation of blue EL. For PeLEDs, high operational stability and efficient blue EL remain to be some of the most pressing goals. To accelerate further developments in these areas, the recent progress in the research of PeLEDs is reviewed. The authors attempt to establish preliminary connections between the degradation mechanisms and the strategies for improvements, exemplified by a selection of recent representative works in the field. Lessons learned from organic LEDs and perovskite solar cells point toward some of the most important directions. This progress report serves as a catalyst for further interdisciplinary research involving materials scientists, chemists, and physicists working together to realize operationally stable PeLEDs. [ABSTRACT FROM AUTHOR]

Copper and gold halide and pseudo-halide complexes stabilised by methyl-, ethyl- and adamantyl-substituted cyclic (alkyl)(amino)carbene (CAAC) ligands are mostly linear monomers in the solid state, without aurophilic Au⋅⋅⋅Au interactions. (Et2L)CuCl shows the highest photoluminescence quantum yield (PLQY) in the series, 70 %. The photoemissions of Me2L and Et2L copper halide complexes show S1→S0 fluorescence on the ns time scale, in agreement with theory, as well as a long-lived emission. Monomeric (Me2L)CuNCS is a white emitter, whereas dimeric [(Et2L)Cu(μ-NCS)]2 shows intense yellow emission with a photoluminescence (PL) quantum yield of 49 %. The reaction of (AdL)MCl (M=Cu or Au) with phenols ArOH (Ar=Ph, 2,6-F2C6H3, 2,6-Me2C6H3, 3,5- tBu2C6H3, 2- tBu-5-MeC6H3, 2-pyridyl), thiophenol, or aromatic amines H2NAr′′ (Ar′=Ph, 3,5-(CF3)2C6H3, C6F5, 2-py) afforded the corresponding phenolato, thiophenolato and amido complexes. Although the emission wavelengths are only marginally affected by the ring substitution pattern, the PL intensities respond sensitively to the presence of substituents in the ortho or meta positions. In gold aryloxides, PL is controlled by steric factors, with strong luminescence in compounds with Au- O-C-C torsion angles <50°. Calculations confirm the dependence of oscillator strength on the torsion angle, as well as the inter-ligand charge transfer nature of the emission. The HOMO/LUMO energy levels were estimated based on first reduction and oxidation potentials. [ABSTRACT FROM AUTHOR]

ABSTRACT An all-Si tandem solar cell has the potential to achieve high conversion efficiency at low cost. However, the selection and synthesis of candidate material remain challenging. In this work, we show that the conventional 'Si quantum dots (Si QDs) in SiO2 matrix' approach can lead to the formation of over-sized Si nanocrystals especially when doped with phosphorous, making the size-dependent quantum confinement less effective. Also, our investigation has shown that the high resistivity of this material has become the performance bottleneck of the solar cell. To resolve these matters, we propose a new design based on Si QDs embedded in a SiO2/Si3N4 hybrid matrix. By replacing the SiO2 tunnel barriers by the Si3N4 layers, the new material manages to constrain the growth of doped Si QDs effectively and enhances the apparent band gap, as shown in X-ray diffraction, Raman, photoluminescence and optical spectroscopic measurements. Besides, electrical characterisation on Si QD/c-Si heterointerface test structures indicates the new material possesses improved vertical carrier transport properties. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Nanowire lasers hold great potential as nanoscale coherent light sources. The rapid wavelength tuning of such light sources is one of the most important parameters for practical applications. Although significant efforts have been made in the past decades, the fast and reversible lasing wavelength tuning in nanowires or structures alike remains a challenge. Here, by incorporating temperature‐dependent Varshni shift of the bandgap with ultralow thermal inertia of a free‐standing cadmium sulfide (CdS) nanowire, a fast lasing wavelength tuning in single nanowires with excellent reversibility is demonstrated. Above room temperature, a Varshni shift rate (≈0.16 nm K−1) twice larger than that at low temperature (≈ 0.085 nm K−1) is observed, and the nanowire lasing peak is tuned from 514 to 549 nm with step down to 0.075 nm K−1. Using a beam of CO2 laser pulses to instantaneously modulate the temperature of a free‐standing lasing nanowire, a reversible wavelength tuning at a rate of ≈48 000 nm s−1, which is about three orders of magnitude faster than that reported previously is achieved. The results herein suggest a very promising route to fast wavelength tuning in lasing nanowires or other nanostructures, which may lead to fast tunable nanolasers for a variety of nanophotonic applications. [ABSTRACT FROM AUTHOR]

Carbene metal amides are a new class of highly efficient light‐emitting molecules based on a linear donor–metal–acceptor geometry. Here the synthesis, structure, and photo‐ and electroluminescence of carbene silver carbazolato complexes, (AdL)Ag(Cz) [AdL = adamantyl‐substituted cyclic (alkyl)(amino)carbene; Cz = carbazolate (1) and 3,6‐tBu2Cz (2)], are reported. They display green emission with photoluminescence quantum yields of up to 74%. Efficient mixing of triplet and singlet excited states is observed, with sub‐microsecond thermally activated radiative triplet lifetimes. These complexes provide prototype organic light‐emitting diodes based exclusively on silver emitters, with external quantum efficiencies of up to 14%. Carbene‐metal‐amides based on silver allow organic light‐emitting diode (OLED) fabrication by both solution and thermal vapor deposition techniques. Rotational flexibility leads to a thermally activated delayed fluorescence type process with very low activation energy and sub‐microsecond triplet harvesting. These are the first OLEDs based solely on silver. [ABSTRACT FROM AUTHOR]