A Spacer Cation Assisted Nucleation and Growth Strategy Enables Efficient and High‐Luminance Quasi‐2D Perovskite LEDs

Quasi‐2D Ruddlesden‐Popper perovskites receive tremendous attention for application in light‐emitting diodes (LEDs). However, the role of organic ammonium spacers on perovskite film has not been fully‐understood. Herein, a spacer cation assisted perovskite nucleation and growth strategy, where guanidinium (GA+) spacer is introduced into the perovskite precursor and at the interface between the hole transport layer (HTL) and the perovskite, to achieve dense and uniform perovskite films with enhanced optical and electrical performance is developed. A thin GABr interface pre‐formed on HTL provides more nucleation sites for perovskite crystal; while the added GA+ in perovskite reduces the crystallization rate due to strong hydrogen bonding interacts with intermediates, which promotes the growth of enhanced‐quality quasi‐2D perovskite films. The ionized ammonium group ( NH3+) of GA+ also favors formation of polydisperse domain distribution, and amine or imine ( NH2 or NH) group interact with perovskite defects through coordination bonding. The spacer cation assisted nucleation and growth strategy is advantageous for producing efficient and high‐luminance perovskite LEDs, with a peak external quantum efficiency of over 20% and a luminance up to 100 000 cd m−2. This work can inform and underpin future development of high‐performance perovskite LEDs with concurrent high efficiency and brightness

Dual‐Defect Manipulation Enables Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes

Performance of blue solution‐processed perovskite light‐emitting diodes (LEDs) is limited by availability of blue perovskite materials. Herein, 4‐(trifluoromethyl)benzoyl ammonium bromide (4‐TMBABr) is used with abundant N H and C O groups to passivate the defects and produce highly stable PEAxPA2‐x(CsPbBr3)n‐1PbBr4 perovskites for blue LED applications. The N H group in the 4‐TMBABr suppresses the Br‐ion mismatch through hydrogen bonds (N‐H···Br) and C O group coordinates the unsaturated lead dangling bonds (C O:Pb). The effective defect passivation by 4‐TMBABr reduces the nonradiative recombination in the perovskite films, hence enhancing its optical performance. In the LED structure, the sodium bis(trifluoromethanesulfonyl)imide (SBTI) modified NiOx films are used to improve the hole transport and to inhibit the fluorescence quenching of the perovskite layer. The dual‐defect manipulation strategy is advantageous for producing efficient and spectrally stable blue perovskite LEDs, and the authors demonstrate an LED with maximum luminance of 1094 cd m−2 and external quantum efficiency of 10.3%. This work can inform and underpin future development of blue perovskite LEDs with highly efficient and stabile performance

Glutathione de Novo Synthesis but Not Recycling Process Coordinates with Glutamine Catabolism to Control Redox Homeostasis and Directs Murine T Cell Differentiation

Upon antigen stimulation, T lymphocytes undergo dramatic changes in metabolism to fulfill the bioenergetic, biosynthetic and redox demands of proliferation and differentiation. Glutathione (GSH) plays an essential role in controlling redox balance and cell fate. While GSH can be recycled from Glutathione disulfide (GSSG), the inhibition of this recycling pathway does not impact GSH content and murine T cell fate. By contrast, the inhibition of the de novo synthesis of GSH, by deleting either the catalytic (Gclc) or the modifier (Gclm) subunit of glutamate–cysteine ligase (Gcl), dampens intracellular GSH, increases ROS, and impact T cell differentiation. Moreover, the inhibition of GSH de novo synthesis dampened the pathological progression of experimental autoimmune encephalomyelitis (EAE). We further reveal that glutamine provides essential precursors for GSH biosynthesis. Our findings suggest that glutamine catabolism fuels de novo synthesis of GSH and directs the lineage choice in T cells

Pengaruh Pendekatan Pembelajaran Matematika Realistik Terhadap Prestasi Belajar Matematika Ditinjau Dari Kemampuan Numerik Siswa Kelas VIII SMP Negeri 2 Amlapura

Penelitian ini bertujuan untuk mengetahui dan mendeskripsikan pengaruh pendekatan pembelajaran matematika realistik terhadap prestasi belajar matematika ditinjau dari kemampuan numerik siswa. Penelitian ini merupakan eksperimen semu dilaksanakan dengan menggunakan rancangan the post test only control group design. Populasinya adalah seluruh siswa kelas VIII SMP Negeri 2 Amlapura tahun pelajaran 2013-2014. Dari delapan kelas yang ada, empat kelas dipilih sebagai sampel yakni dua kelas sebagai kelas eksperimen dan dua kelas sebagai kelas kontrol yang diambil dengan teknik random. Data penelitian dikumpulkan menggunakan tes, yaitu tes kemampuan numerik dan tes prestasi belajar matematika. Data yang diperoleh dianalisis dengan analisis varians dua jalur dilanjutkan dengan uji Tukey. Berdasarkan hasil analisis data dan pembahasan, dapat disimpulkan, terdapat perbedaan yang signifikan prestasi belajar matematika antara siswa yang mengikuti pendekatan pembelajaran matematika realistik dengan siswa yang mengikuti pendekatan pembelajaran konvensional. Terdapat pengaruh interaksi antara pendekatan pembelajaran matematika realistik dan kemampuan numerik terhadap prestasi belajar matematika. Pada Siswa yang memiliki kemampuan numerik tinggi, prestasi belajar matematika siswa yang mengikuti pendekatan pembelajaran matematika realistik lebih baik daripada pendekatan konvensional. Pada siswa yang memiliki kemampuan numerik rendah, prestasi belajar matematika siswa yang mengikuti pendekatan pembelajaran matematika realistik tetap lebih tinggi dari siswa yang mengikuti pendekatan pembelajaran konvensional.Kata Kunci : pendekatan pembelajaran matematika realistik, kemampuan numerik, dan prestasi belajar matematika The study aimed at finding out and describing the contribution of realistic mathematic instructional approach towards mathematic learning achievement viewed from numeric skills. It was a quasi-experimental research by utilizing the post test only control group design. The study involved all students class VIII SMP Negeri 2 Amlapura in 2013-2014 as the population. Four classes of the students were chosen from eight parallel classes as the samples consisting of two classes as experimental and another two classes as control groups. They were determined based on random technique. The data were collected by testing, involving numeric ability and mathematic achievement tests. They were analysed based on two tailed variant analysis followed by Tukey-test. The results indicated that there was a significant difference between mathematic learning achievement of the students joining realistic mathematic instruction and those joining a conventional approach. There was an interactional contribution of realistic mathematic instructional approach and numeric ability towards mathematic learning achievement. The students having higher numeric skills, when joining realistic mathematic instruction approach their mathematic learning achievement was found better or higher than those joining a conventional approach. The students having lower numeric skills, when joining realistic mathematic instruction approach, their mathematic learning achievement was found better or higher than those joining a conventional approach

Core/Shell Metal Halide Perovskite Nanocrystals for Optoelectronic Applications

© 2021 Wiley-VCH GmbH Core/shell structured metal halide perovskite nanocrystals (NCs) are emerging as a type of material with remarkable optical and electronic properties. Research into this field has been developing and expanding rapidly in recent years, with significant advances in the studies of the shell growth mechanism and in understanding of properties of these materials. Significant enhancement of both the stability and the optical performance of core/shell perovskite NCs are of particular importance for their applications in optoelectronic technologies. In this review, the recent advances in core/shell structured perovskite NCs are summarized. The band structures and configurations of core/shell perovskite NCs are elaborated, the shell classification and shell engineering approaches, such as perovskites and their derivative shells, semiconductor shell, oxide shell, polymer shell, etc. are reviewed, and the shell growth mechanisms are discussed. The prospective of these NCs in lighting and displays, solar cells, photodetectors, and other devices is discussed in the light of current knowledge, remaining challenges, and future opportunities

Highly flexible, electrically driven, top-emitting, quantum dot light-emitting stickers

Flexible information displays are key elements in future optoelectronic devices. Quantum dot light-emitting diodes (QLEDs) with advantages in color quality, stability, and cost-effectiveness are emerging as a candidate for single-material, full color light sources. Despite the recent advances in QLED technology, making high-performance flexible QLEDs still remains a big challenge due to limited choices of proper materials and device architectures as well as poor mechanical stability. Here, we show highly efficient, large-area QLED tapes emitting in red, green, and blue (RGB) colors with top-emitting design and polyimide tapes as flexible substrates. The brightness and quantum efficiency are 20 000 cd/m2 and 4.03%, respectively, the highest values reported for flexible QLEDs. Besides the excellent electroluminescence performance, these QLED films are highly flexible and mechanically robust to use as electrically driven light-emitting stickers by placing on or removing from any curved surface, facilitating versatile LED applications. Our QLED tapes present a step toward practical quantum dot based platforms for high-performance flexible displays and solid-state lighting. © 2014 American Chemical Society

Efficient quantum dot light emitting diodes for solid state lighting and displays

Quantum dot-based light-emitting diodes (QLEDs) with advantages in colour quality, stability and cost-effectiveness are emerging as a candidate for single-material, full colour light sources. The focus of this study is to solve some challenging problems that hinder the ultimate research transformation and commercialization of the QLED technology. Our light out-coupling strategy enhanced device efficiency up to 9.34%, the record high value for green QLEDs. The substitution of organic charge transport layers with metal oxide nanoparticles significantly improved the operating lifetime of QLEDs by a factor of 20. Our development of the narrowest-linewidth, high-quality InP-based QDs with wavelength tunability across full visible spectrum solved the toxicity problem of QDs effectively. The use of Kapton tape and metal electrodes in top-emitting LED architecture made a significant breakthrough in flexible QLED performance with the best efficiency of 4.03%. Our study reported in this thesis contributed to the fast development of the QLEDs.DOCTOR OF PHILOSOPHY (EEE