device stability impedes its commercialization, mainly stemming from the chemical decomposition of regular 3D perovskites in damp environment. [3,4] Encapsulation techniques can slow down the degradation process, but the essential approach to tackle this issue is to find stable perovskite materials capable of achieving long-term stability. [5] In contrast to traditional 3D counterparts, quasi-2D layered perovskites have shown enhanced stability owing to the bulkier and hydrophobic organic molecule in the structure, and have been applied both in photovoltaics and light-emitting diodes. [6][7][8][9] Quasi-2D perovskites take the generic structural formula of L 2 S n−1 M n X 3n+1 , where n is an integer, M is a divalent metal, X is a halide anion, and L and S are organic cations with large and small sizes, respectively. [10] Layered structures are usually formed by inserting the large-sized organic cation spacers into the inorganic sheets of corner-sharing [MX 6 ] octahedra. These quasi-2D compounds can be regarded as natural formed quantum-well (QW) structures, in which the semiconducting inorganic sheets act as the wells and the organic dielectric layers correspond to the Quasi-2D layered organometal halide perovskites have recently emerged as promising candidates for solar cells, because of their intrinsic stability compared to 3D analogs. However, relatively low power conversion efficiency (PCE) limits the application of 2D layered perovskites in photovoltaics, due to large energy band gap, high exciton binding energy, and poor interlayer charge transport. Here, efficient and water-stable quasi-2D perovskite solar cells with a peak PCE of 18.20% by using 3-bromobenzylammonium iodide are demonstrated. The unencapsulated devices sustain over 82% of their initial efficiency after 2400 h under relative humidity of ≈40%, and show almost unchanged photovoltaic parameters after immersion into water for 60 s. The robust performance of perovskite solar cells results from the quasi-2D perovskite films with hydrophobic nature and a high degree of electronic order and high crystallinity, which consists of both ordered large-bandgap perovskites with the vertical growth in the bottom region and oriented smallbandgap components in the top region. Moreover, due to the suppressed nonradiative recombination, the unencapsulated photovoltaic devices can work well as light-emitting diodes (LEDs), exhibiting an external quantum efficiency of 3.85% and a long operational lifetime of ≈96 h at a high current density of 200 mA cm −2 in air.

Controlled synthesis and toughening mechanisms of an all-purpose hyperbranched modifier, which can form non-phase-separated networks with simultaneous enhancements in Tg, modulus, impact and tensile strengths.

Tin-based halide perovskites have attracted considerable attention for nontoxic perovskite light-emitting diodes (PeLEDs), but the easy oxidation of Sn 2+ and nonuniform film morphology cause poor device stability and reproducibility. Herein, we report a facile approach to achieve efficient and stable lead-free PeLEDs by using tinbased perovskite multiple quantum wells (MQWs) for the first time. On the basis of various spectroscopic investigations, we find that the MQW structure not only facilitates the formation of uniform and highly emissive perovskite films but also suppresses the oxidation of Sn 2+ cations. The tin-based MQW PeLED exhibits a peak external quantum efficiency of 3% and a high radiance of 40 W sr −1 m −2 with good reproducibility. Significantly, these devices show excellent operational stability with over a 2 h lifetime under a constant current density of 10 mA cm −2 , which is comparable to that of leadbased PeLEDs. These results suggest that perovskite MQWs can provide a promising platform for achieving high-performance lead-free PeLEDs.

Solution-processable perovskites show highly emissive and good charge transport, making them attractive for low-cost light-emitting diodes (LEDs) with high energy conversion efficiencies. Despite recent advances in device efficiency, the stability of perovskite LEDs is still a major obstacle. Here, we demonstrate stable and bright perovskite LEDs with high energy conversion efficiencies by optimizing formamidinium lead iodide films. Our LEDs show an energy conversion efficiency of 10.7%, and an external quantum efficiency of 14.2% without outcoupling enhancement through controlling the concentration of the precursor solutions. The device shows low efficiency droop, i.e. 8.3% energy conversion efficiency and 14.0% external quantum efficiency at a current density of 300 mA cm −2 , making the device more efficient than state-of-the-art organic and quantum-dot LEDs at high current densities. Furthermore, the half-lifetime of device with benzylamine treatment is 23.7 hr under a current density of 100 mA cm −2 , comparable to the lifetime of near-infrared organic LEDs.

Synthesis of epoxide-terminated hyperbranched polyethers (EHBPEs) with different backbone stiffness and molecular weight (MW) are obtained using simple one-pot A 2 +B 3 approach. When used as tougheners for DGEBA/TETA system, non-phase-separated cured networks are always obtained. Effects of MW and backbone stiffness on the toughening performance were systematically investigated. Among the EHBPEs studied, EHBPE-4C which has the lowest MW and stiffest backbone and EHBPE-10C 10 which has the highest MW and most flexible backbone can simultaneously improve toughness, tensile strength, and T g . In contrast, addition of EHBPE-6C and EHBPE-8C, which have medium MW and backbone stiffness, lead to incomplete cure and cannot improve or worsen the toughness and tensile strength. Both stiffness and MW of hyperbranched polyether play important roles in determining the crosslink density and structure of non-phase-separated networks, which dictate the toughness strength and 15

Solution‐processed, self‐organized multiple quantum well (MQW) perovskites possess good film coverage and high photoluminescence quantum efficiency, which are promising for high performance light‐emitting diodes (LEDs). However, due to the inclusion of insulating large organic cation as barrier layer, the charge transport in MQW perovskites is not as efficient as 3D perovskites, which limits the improvement of power conversion efficiency of MQW perovskite LEDs. Here, it is demonstrated that by molecular engineering, the conductivity of MQW perovskite film can be effectively increased by reducing the barrier width in QWs, thus leading to enhanced device performance. By controlling the constitution of the narrow‐barrier‐width MQW perovskites, one can achieve green LEDs with a high luminance of 30 000 cd m−2 at a low voltage of 6 V and a peak external quantum efficiency of 7.7%. Moreover, the green perovskite LEDs show a lifetime of 63 min with initial luminance of 1330 cd m−2, representing one of the best performing green perovskite LEDs. Here, a promising strategy is provided to further boost the efficiency, brightness, and stability of MQW perovskite LEDs.

perovskites incorporating hydrophobic organic spacer cations show improved film stability and morphology compared to their three-dimensional (3D) counterparts. However, 2D perovskites usually exhibit low photoluminescence quantum efficiency (PLQE) owing to strong exciton-phonon interaction at room temperature, which

Tetrafunctional epoxy is an indispensable matrix for the aerospace industry, high-temperature adhesives, and encapsulation materials, where high service temperatures (>220 °C) are required. N,N,N′,N′-Tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) has long been the dominant candidate in those applications; however, fully cured TGDDM epoxy materials suffer from poor toughness, unwanted side reactions, and inadequate moisture resistance. A novel tetrafunctional epoxy, TFTE, is synthesized to address those issues, which have not been resolved for decades. TFTE can be prepared through a simple three-step procedure using readily available raw materials. Each step shows a high yield (>90%) and involves only mild reaction conditions. When TFTE is mixed with diglycidyl ether of bisphenol A (DGEBA) and cured with 4,4′-diaminodiphenylsulfone (DDS), the cured epoxy shows a T g value of 252 °C, a tensile strength of 80.0 MPa, and, more importantly, a higher toughness (29.8 kJ/m2) and better moisture resistance than the TGDDM/DDS system. In addition, the interfacial strength, thermal stability, and processability of TFTE/DGEBA are comparable to those of TGDDM. These excellent properties and processability make TFTE a potential replacement for TGDDM.