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.
The barrier width of multiple quantum well (MQW) perovskite is controlled through molecular engineering of the large organic cation. MQW perovskite films based on a novel benzimidazolium exhibit reduced barrier width and enhanced conductivity, leading to green perovskite light‐emitting diodes with high luminance and good stability.
Abstract
Developing open-shell singlet (OS) diradicals with high luminescent properties and exceptional single-molecule magnetoluminescence (ML) performance is extremely challenging. Herein, we ...propose a concept to enhance luminescent efficiency by adjusting the donor conjugation of OS diradicals, thereby achieving a highly luminescent diradical, DR1, with outstanding stability and making it a viable option for use in the emitting layer of organic light-emitting diodes (OLEDs). More importantly, the 0.5 wt%-DR1 doped film demonstrates significant single-molecule magnetoluminescence (ML) properties. A giant ML value of 210% is achieved at a magnetic field of 7 T, showing the great potential of DR1 in magneto-optoelectronic devices.
Controlling contact resistance in organic field‐effect transistors (OFETs) is one of the major hurdles to achieve transistor scaling and dimensional reduction. In particular in the context of ...ambipolar and/or light‐emitting OFETs it is a difficult challenge to obtain efficient injection of both electrons and holes from one injecting electrode such as gold since organic semiconductors have intrinsically large band gaps resulting in significant injection barrier heights for at least one type of carrier. Here, systematic control of electron and hole contact resistance in poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) ambipolar OFETs using thiol‐based self‐assembled monolayers (SAMs) is demonstrated. In contrast to common believe, it is found that for a certain SAM the injection of both electrons and holes can be improved. This simultaneous enhancement of electron and hole injection cannot be explained by SAM‐induced work‐function modifications because the surface dipole induced by the SAM on the metal surface lowers the injection barrier only for one type of carrier, but increases it for the other. These investigations reveal that other key factors also affect contact resistance, including i) interfacial tunneling through the SAM, ii) SAM‐induced modifications of interface morphology, and iii) the interface electronic structure. Of particular importance for top‐gate OFET geometry is iv) the active polymer layer thickness that dominates the electrode/polymer contact resistance. Therefore, a consistent explanation of how SAM electrode modification is able to improve both electron and hole injection in ambipolar OFETs requires considering all mentioned factors.
SAM modification in ambipolar transistors is able to improve both electron and hole injection. The results reported here show that gold electrodes modified by 1DT exhibit improved contact resistance for both electrons and holes compared to O2 plasma‐treated gold electrodes. The origin of this unexpected behavior is investigated in terms of SAM‐induced change of work‐function, film thickness, interfacial tunneling resistance and interfacial electronic and molecular structure.
We demonstrate the use of a cross-linking chemistry for an amorphous fluoropolymer gate dielectric, poly(perfluorobutenylvinylether) commercially known as Cytop. Spin-coated films of Cytop exhibit ...good gate insulating properties as well as provide excellent OFET operational stability. However, these devices operate at large voltages because the dielectric layer thickness is typically ∼450−600 nm. When the thickness of a Cytop dielectric layer is decreased below 200 nm, the device yields are dramatically reduced due to pinhole formation. Our new cross-linked Cytop (C-Cytop) formulation deposited by spin-coating enables uniform thin films on top of various organic semiconductors that exhibits low gate leakage current densities (<10 nA mm−2) and high dielectric breakdown strengths (>2 MV cm−1). Our approach results in C-Cytop dielectric films as thin as 50 nm, thus allowing the fabrication of reliable p- and n-channel top-gate OFETs operating at very low-voltages (<5 V). The most remarkable properties of this new C-Cytop gate dielectric are the excellent device yields (∼100%) for thicknesses <100 nm and the dramatically reduced sensitivity to the underlying semiconductor film morphology. This new approach represents a significant advance compared to cross-linked PMMA films (C-PMMA) and other nonfluorinated polymer dielectrics on identical test structures. Furthermore, C-Cytop-based OFETs exhibit reduced bias stress and better air stability with respect to C-PMMA because of the inert perfluorinated chemical structure of this polymer. Finally, direct spectroscopic evidence of the cross-linking process was obtained by Fourier transform infrared (FTIR) spectroscopy, demonstrating complete reaction in air and at room temperature.
Control of the hierarchical molecular organization of polydiarylfluorenes by synthetic strategies is significant for optimizing photophysical properties as well as the performance of light-emitting ...devices. Herein, for the suppression of molecular aggregation and enhancement of luminescence efficiency, a series of steric units were introduced into polydiarylfluorenes by copolymerization, with the aim of integrating the advantages of the steric-hindrance effect and of the β-phase. Optical and Raman spectroscopies revealed a β-phase conformation for a polymer copolymerized with spirofluorene-9,9′-xanthene (SFX), with photoluminescence (PL) peaks at 454, 482, and 517 nm. Moreover, the morphological stability and electroluminescence (EL) stability were also improved without compromising the performance of the polymer light-emitting diodes (PLEDs). Furthermore, three steric-hindrance-functionalized copolymers showed significantly decreased thresholds for amplified spontaneous emission (E th ASE) and enhanced stability following thermal annealing treatment. These results indicate that steric-hindrance functionalization is a superior approach to improve the overall stability and optoelectronic properties for blue-light-emitting π-conjugated polymers.
We report the formation of high-quality Cs0.4MA0.6PbBr3 thin films with nearly full surface coverage and good emission properties upon the introduction of Cs^＋ into perovskite crystals. The ...Cs0.4MA0.6PbBr3 thin films were applied as emissive layers in light-emitting diodes. A maximum external quantum efficiency of -2.0% was achieved for these green-emitting devices.
We demonstrate hole-transport-layer-free light-emitting diodes (LEDs) based on solution-processed multiple-quantum-well (MQW) perovskite. The MQW perovskite can self-assemble to a unique structure of ...vertically graded distribution with two-dimensional layered perovskite covered by three-dimensional-like perovskite at top, which can naturally form a barrier of electron transporting to the anode interface, thereby enhancing the charge capture efficiency. This leads to hole-transport-layer-free MQW perovskite LEDs reaching an external quantum efficiency (EQE) of 9.0% with emission peak at 528 nm, which is over 6 times of LEDs based on three-dimensional perovskite with the same device structure, representing the record EQE of hole-transport-layer-free perovskite LED.
Efficient hole-transport-layer-free light-emitting diodes are achieved based on self-assembled multiple-quantum-well perovskites. Display omitted
This study sought to use a newly developed intracellular ATP delivery to enhance incisional wound healing to reduce surgical wound dehiscence and to explore possible mechanism for this effect. ...Thirty-five adult New Zealand white rabbits were used. Skin incisions were made on the back and closed. ATP-vesicles were mixed with a neutral cream for one side of the wounds while the neutral cream alone was used on the other side of the wounds. Laser speckle contrast imaging (LSCI), biomechanical, histological, and immunohistochemical analyses were performed 7 and 14 days after surgery, and macrophage culture was used to test the enhanced collagen production ability. Among them, 10 were used for wound perfusion study and 25 were used for wound biomechanical and histological/immunohistochemical studies. Wound tissue perfusion was reduced after surgery especially in early days. Wound tissue tensile strength, breaking stress, and elasticity were all much higher in the ATP-vesicle treated group than in the cream treated group at days 7 and 14. The healing was complemented by earlier macrophage accumulation,
in situ
proliferation, followed by direct collagen production. The results were further confirmed by human macrophage culture. It was concluded that intracellular ATP delivery enhanced healing strength of incisional wounds
via
multiple mechanisms.
Metal halide perovskites have advanced greatly in both light-emitting diodes (LEDs) and photovoltaics (PVs) through delicate device engineering. The optimization strategies of perovskite LEDs and PVs ...have been demonstrated to be quite different. Here, we show that this dissimilarity in device fabrications can be well understood based on the analysis of carrier dynamics in LEDs and PVs.
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