Quantum dot light‐emitting diodes (QLEDs) are one of the most promising candidates for next‐generation displays and lighting sources, but they are barely used because vulnerability to electrical and thermal stresses precludes high brightness, efficiency, and stability at high current density (J) regimes. Here, bright and stable QLEDs on a Si substrate are demonstrated, expanding their potential application boundary over the present art. First, a tailored interface is granted to the quantum dots, maximizing the quantum yield and mitigating nonradiative Auger decay of the multiexcitons generated at high‐J regimes. Second, a heat‐endurable, top‐emission device architecture is employed and optimized based on optical simulation to enhance the light outcoupling efficiency. The multilateral approaches realize that the red top‐emitting QLEDs exhibit a maximum luminance of 3 300 000 cd m−2, a current efficiency of 75.6 cd A−1, and an operational lifetime of 125 000 000 h at an initial brightness of 100 cd m−2, which are the highest of the values reported so far.
of their emission spectra, and high photoluminescence (PL) quantum yield (QY), owing to the quantum confinement effect. Also, they can be processed as dispersed in solution for their practical application to optoelectronic devices. [1][2][3][4] In particular, QD-based light-emitting diodes (QLEDs) are considered as a prospective device for realizing wide color gamut (WCG) displays.Among the elements composing QDs, nondegradable heavy metals, such as Cd, are known to be highly toxic to the environment. [5] The use of these hazardous materials has been limited by regulations and expected to be prohibited in the near future. Thus, a few heavy metal-free QDs are attracting interests, and InP QDs are considered as the most promising candidate because of their wide coverage in the entire visible spectral ranges and high PL QY. [6,7] The synthesis methods and the properties of InP QDs have been developed for a decades, and as a result, the performance of the InP-based QLEDs has been improved. [8][9][10] For instance, Lim et al. reported InP-based green QLEDs using (poly [(9,9-bis(30-(N,N-dimethylamino)propyl)-2,7-fluorene)alt-2,7-(9,9-ioctylfluorene) (PFN) as an interlayer between the electron transport layer (ETL) and the emissive layer (EML) and a thick ZnSeS heterostructured shell to enhance the electronhole balance and to reduce the Auger recombination process. [9] Zhang et al. also reported green QLEDs using InP/GaP/ZnS QDs with a thick shell which can reduce nonradiative Föster resonant energy transfer between QDs. [10] However, as summarized in Table S1 in the Supporting Information, their highest current efficiencies were <14 cd A −1 , the maximum luminance (L) were a few thousands cd m −2 , and the FWHM of their spectra were >50 nm, which are far behind the requirements for practical use.Considering the decent intrinsic properties of the recent InP QDs, the device architecture should be advanced for Cdfree QLEDs to improve their performance. So far, the bottom emission devices which emit light through the glass substrate have been widely used for QLEDs. However, the top emission structure, which emits light through the top semitransparent electrodes, has several advantages for their use in display devices, such as high aperture ratios, efficient light outcoupling, InP quantum dots (QDs) based light-emitting diodes (QLEDs) are considered as one of the most promising candidates as a substitute for the environmentally toxic Cd-based QLEDs for future displays. However, the device architecture of InP QLEDs is almost the same as the Cd-based QLEDs even though the properties of Cd-based and InP-based QDs are quite different in their energy levels and shapes. Thus, it is highly required to develop a proper device structure for InP-based QLEDs to improve the efficiency and stability. In this work, efficient, bright, and stable InP/ZnSeS QLEDs based on an inverted top emission QLED (ITQLED) structure by newly introducing a "hole-suppressing interlayer" are demonstrated. The green-emitting ITQLEDs with the hole-suppressin...
We demonstrated modulation of charge carrier densities in all-solution-processed organic field-effect transistors (OFETs) by modifying the injection properties with self-assembled monolayers (SAMs). The all-solution-processed OFETs based on an n-type polymer with inkjet-printed Ag electrodes were fabricated as a test platform, and the injection properties were modified by the SAMs. Two types of SAMs with different dipole direction, thiophenol (TP) and pentafluorobenzene thiol (PFBT) were employed, modifying the work function of the inkjet-printed Ag (4.9 eV) to 4.66 eV and 5.24 eV with TP and PFBT treatments, respectively. The charge carrier densities were controlled by the SAM treatment in both dominant and non-dominant carrier-channel regimes. This work demonstrates that control of the charge carrier densities can be efficiently achieved by modifying the injection property with SAM treatment; thus, this approach can achieve polarity conversion of the OFETs.
The rising demand for eradicating hazardous substances in the workplace has motivated vigorous researches on environmentally sustainable manufacturing processes of colloidal quantum dots (QDs) for their optoelectronic applications. Despite remarkable achievements witnessed in QD materials (e.g., Pb-or Cd-free QDs), the progress in the eco-friendly process is far falling behind and thus the practical use of QDs. Herein, a complete "green" process of QDs, which excludes environmentally unfriendly elements from QDs, ligands, or solvents, is presented. The implant of mono-2-(methacryloyloxy)ethyl succinate (MMES) ligands renders InP/ZnSe x S 1−x QDs dispersed in eco-friendly polar solvents that are widely accepted in the industry while keeping the photophysical properties of QDs unchanged. The MMES-capped QDs show exceptional colloidal stabilities in a range of green polar solvents that permit uniform inkjet printing of QD dispersion. In addition, MMES-capped QDs are also compatible with commercially available photo-patternable resins, and the cross-linkable moiety within MMES further facilitates the achievement in the formation of well-defined, micrometer-scale patterning of QD optical films. The presented materials, all composed of simple, scalable, and environmentally safe compounds, promise low environmental impact during the processing of QDs and thus will catalyze the practicable use of QDs in a variety of optoelectronic devices.
We present ligand-asymmetric Janus quantum dots (QDs) to improve the device performance of quantum dot light-emitting diodes (QLEDs). Specifically, we devise blue QLEDs incorporating blue QDs with asymmetrically modified ligands, in which the bottom ligand of QDs in contact with ZnO electron-transport layer serves as a robust adhesive layer and an effective electron-blocking layer and the top ligand ensures uniform deposition of organic hole transport layers with enhanced hole injection properties. Suppressed electron overflow by the bottom ligand and stimulated hole injection enabled by the top ligand contribute synergistically to boost the balance of charge injection in blue QDs and therefore the device performance of blue QLEDs. As an ultimate achievement, the blue QLED adopting ligand-asymmetric QDs displays 2-fold enhancement in peak external quantum efficiency (EQE = 3.23%) compared to the case of QDs with native ligands (oleic acid) (peak EQE = 1.49%). The present study demonstrates an integrated strategy to control over the charge injection properties into QDs via ligand engineering that enables enhancement of the device performance of blue QLEDs and thus promises successful realization of white light-emitting devices using QDs.
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