Organic light emitting diodes (OLEDs) employing organic thin‐film based emitters have attracted tremendous attention due to their widespread applications in lighting and as displays in mobile devices and televisions. The novel thin‐film photovoltaic techniques using organic or organic–inorganic hybrid materials such as organic photovoltaics (OPVs) and perovskite solar cells (PSCs) have become emerging competitive candidates with regard to the traditional photovoltaic techniques on account of high‐efficiency, low‐cost, and simple manufacturing processing properties. However, OLEDs, OPVs, and PSCs are vulnerable to the undesired degradation induced by moisture and oxygen. To afford long‐term stability, a robust encapsulation technique by employing materials and structures that possess high barrier performance against oxygen and moisture must be explored and employed to protect these devices. Herein, the recent progress on specific encapsulation materials and techniques for three types of devices on the basis of fundamental understanding of device stability is reviewed. First, their degradation mechanisms, as well as, influencing factors are discussed. Then, the encapsulation technologies and materials are classified and discussed. Moreover, the advantages and disadvantages of various encapsulation technologies and materials coupled with their encapsulation applications in different devices are compared. Finally, the ongoing challenges and future perspectives of encapsulation frontier are provided.
Herein, we propose an effective strategy to enhance the electrochemical activity of metal organic framework-based (MOF) electrode material for electrochemical capacitors. The fabrication involves the synthesis of CuO nanowires on...
A series of bi-transition-metal
hybrids Cu3–x
Ni
x
Al-LDH/rGO (x = 2.5, 2.0, 1.5) were synthesized
via a facile preadjusted
pH citric-acid-assisted coprecipitation method. Systematic characterizations
suggest that the hybrids show honeycomb-like nanosheets array morphology
with ultrathin CuNiAl-LDH nanosheets (∼72.3 × 4.2 nm)
staggered vertically grown on both sides of rGO substrate. The Cu3–x
Ni
x
Al-LDH/rGO
hybrids present a remarkably superior reduction performance for 4-nitrophenol
(4-NP) than pure LDH samples. Particularly, Cu1Ni2Al-LDH/rGO shows the best activity with k
app = 3.4 × 10–2 s–1, ∼1.7-fold
of Cu1Ni2Al-LDH. It is worth noting that the
activity of this bitransition metals hybrid Cu1Ni2Al-LDH/rGO is 37% higher than our previously reported monotransition
metal hybrid Cu1Mg2Al-LDH/rGO (k
app = 2.5× 10–2 s–1). These findings can be ascribed to (1) highly dispersed ultrasmall
Cu2O nanoparticles (∼3.8 nm) instantaneously formed
via in situ reduction of atomic-level dispersed Cu2+ ions
in LDH layer lattices of the Cu3–x
Ni
x
Al-LDH hybrids beneficial from clear
isolation and stabilization effect of Ni–OH; (2) strong promotion
of the doping of atomic-level dispersed Ni2+ ions in LDH
and possible Cu2O–Ni–OH(CuNiAl-LDH)–rGO
three-phase synergistic effect; and (3) enhanced adsorption capacity
for reactants upon π–π stacking and the unique
honeycomb-like nanosheet array morphology. The series of hybrids exhibit
not only excellent reduction properties for varied aromatic nitro
compounds but also good decolorization ability for anionic azo dyes.
Further fixed bed experiments reveal that Cu1Ni2Al-LDH/rGO can efficiently decolorize the mixed solution of 4-NP
and methyl orange at high flow rate (8 mL/min) with TOF of 1.68 ×
10–3 s–1, suggesting great application
potential of the as-obtained nanosheet array bi-transition-metal hybrids
for water remediation.
We combine electron energy-loss spectroscopy and first-principles calculations based on densityfunctional theory (DFT) to identify the lowest indirect exciton state in the in-plane charge response of hexagonal boron nitride (h-BN) single crystals. This remarkably sharp mode forms a narrow pocket with a dispersion bandwidth of ∼ 100 meV and, as we argue based on a comparison to our DFT calculations, is predominantly polarized along the ΓK-direction of the hexagonal Brillouin zone.Our data support the recent report by Cassabois et al. [1] who indirectly inferred the existence of this mode from the photoluminescence signal, thereby establishing h-BN as an indirect semiconductor. 1 arXiv:1706.04806v1 [cond-mat.mes-hall] 15 Jun 2017Hexagonal Boron Nitride (h-BN) is the binary analog of graphite. Like its carbon counterpart, it consists of sp 2 -hybridized hexagonal layers that are stacked along the crystallographic c-axis. This leads to many similarities between these two materials like the applicability as dry lubricants or the possibility to wrap the hexagonal sheets into nanotubes [2,3].More recently, h-BN came into focus in the field of 2D semiconductors, either as a substrate to boost the performance of graphene devices [4] or as an important ingredient in so called van der Waals heterostructures [5]. These overall similarities between the carbon and BN-case notwithstanding, the electronegativity difference between the boron-and nitrogen-atoms has profound implications which show up most prominently in the electronic structure, in particular the fundamental band gap. Though its apparent simplicity in terms of structure and electronic properties, there has been an ongoing argument about the nature and size of the band gap. For a long time, there has been a strong controversy about whether the fundamental gap is direct or indirect and reported values on the size of the gap E G range from below 4 eV to more than 7 eV, depending on the sample quality and the employed method (see e.g. [6,7] for extended compilations of available data on E G ).With time, in particular in the theoretical community, consensus emerged that the gap is indirect [8-10] but still, calculated values differed substantially between 3.9 eV and 5.95 eV.These predictions were, however, strongly challenged by the remarkable observation of a strong photoluminescence (PL) signal in h-BN reported in 2004 [11] which promised great potential for lasing in the deep ultraviolet. Recently, Cassabois et al. [1] took an important step forward in resolving this long-standing debate. They inferred -although only indirectly -the existence of the lowest indirect exciton (iX in their nomenclature) at an energy of 5.955 eV from a careful analysis of detailed PL data thereby establishing h-BN as an indirect semiconductor also from an experimental perspective. They also could show that the presence of sharp excitonic absorption (and/or emission) in a material with an indirect band gap -which appears to contradict the traditional understanding [12] -occurs as a conseq...
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