Efficient and Stable Perovskite Nanocrystal Light-Emitting Diodes with Sulfobetaine-Based Ligand Treatment

Perovskite nanocrystals (PNCs) possess outstanding optical properties such as narrow full-width at half-maximum (fwhm) emission and color tunability. However, the labile ionic nature and weakly bound surface ligands of PNCs result in colloidal instability and crystal structure deformation, thus degrading their optical properties. In this study, we treated CsPbBr3 PNCs with 3-(dodecyldimethyl-ammonio)propane-1-sulfonate (12-SBE) ligands and successfully stabilized the PNCs under ambient air and heat. Under optimum ligand exchange conditions, 12-SBE PNCs showed near 100% photoluminescence quantum yield (PLQY) without an increase in the size of the PNCs. After 12-SBE treatment, the agglomeration of PNCs in solution due to ligand loss was suppressed, and PNC size growth induced by moisture and oxygen under heating was reduced. Finally, we fabricated 12-SBE PNC LEDs exhibiting 6.7% external quantum efficiency (EQE). Moreover, the PL lifetime of 12-SBE PNC LEDs was enhanced 2-fold compared to oleylamine (OAM) PNC LEDs

Importance of Chemical Distortion on the Hysteretic Oxygen Capacity in Li-Excess Layered Oxides

Nonhysteretic redox capacity is a critical factor in achieving high energy density without energy loss during cycling for rechargeable battery electrodes, which has been considered a major challenge in oxygen redox (OR) for Li-excess layered oxide cathodes for lithium-ion batteries (LIBs). Until recently, transition metal migration into the Li metal layer and the formation of O–O dimers have been considered major factors affecting hysteretic oxygen capacity. However, Li-excess layered oxides, particularly Ru oxides, exhibit peculiar voltage hysteresis that cannot be sufficiently described by only these factors. Therefore, this study aims to unlock the critical impeding factors in restraining the non-polarizing oxygen capacity of Li-excess layered oxides (herein, Li2RuO3) that exhibit reversible OR reactions. First, Li2RuO3 undergoes an increase in the chemical potential fluctuation as both the thermodynamic material instability and vacancy content increase. Second, the chemical compression of O–O bonds occurs at the early stage of the OR reaction (0.5 ≤ x ≤ 0.75) for Li1–xRu0.5O1.5, leading to flexible voltage hysteresis. Finally, in the range of 0.75 ≤ x ≤ 1.0, for Li1–xRu0.5O1.5, the formation of an O­(2p)–O­(2p)* antibonding state derived from the structural distortion of the RuO6 octahedron leads to the irreversibility of the OR reaction and enhanced voltage hysteresis. Consequently, our study unlocks the new decisive factor, namely, the structural distortion inducing the O­(2p)–O­(2p)* antibonding state, of the hysteretic oxygen capacity and provides insights into enabling the full potential of the OR reaction for Li-excess layered oxides for advanced LIBs

Physicochemical Screen Effect of Li Ions in Oxygen Redox Cathodes for Advanced Sodium-Ion Batteries

Unlike in lithium-ion batteries (LIBs), in sodium-ion batteries (SIBs), nonhysteretic oxygen redox (OR) reactions are observed in Li-excess Na-layered oxides. This necessitates an understanding of the reaction mechanism of an O3-type Li-excess Mn oxide, Na­[Li1/3Mn2/3]­O2, a novel OR material designed for advanced SIBs. It could establish the role of Li in triggering nonhysteretic oxygen capacities during (de)­sodiation. Three biphasic mechanisms were compared using first-principles calculations under the desodiation modes: (i) Na/vacancy ordering, (ii) Li migration in the NaO2 layer, and (iii) in-plane Mn migration. The migrated Li ions generated a “physicochemical screen” effect upon electrochemical OR reactions in the oxide cathode. Thermodynamic formation energies showed different biphasic pathways upon charging in Na1–x[Li2/6Mn4/6]­O2 (NLMO) under the three modes. O–O bond population indicated that biphasic-reaction paths -i and -iii were derived from generating inter/intralayer O–O dimers, and path-iii was triggered by the formation of a Mn–O2–Mn moiety. However, Li migration exhibited an ideal OR process (O2–/On–) without forming anionic dimers. The electronic structures of Mn­(3d) and O­(2p) revealed that Li migration pushed lattice-based O­(2p)-hole states to a high energy level, resulting in the chemical suppression of O2 molecule formation. Selectively decoupled oxygen ordering indicated that the oxygen species coordinated with two Mn (OMn2) derived from Li migration played an important role in nonhysteretic oxygen capacities during cycling. From these findings, we propose the “physicochemical screen” concept that physically suppresses interlayer O–O dimers and chemically hinders discretized O­(2p)–O­(2p) states formed by molecular O2. This could significantly impact the role of Li ions in Li-excess OR-layered oxides for SIBs

Robust Heteroepitaxial Growth of GaN Formulated on Porous TiN Buffer Layers

Gallium nitride (GaN) heteroepitaxial growth is widely studied as a semiconductor material due to its various benefits. Especially, development of a buffer layer between GaN and the substrate verifies to be an effective strategy to reduce high threading dislocation density. However, the buffer layer often impedes strong adhesion between the epilayer and foreign substrate because thermally induced residual stress often causes delamination of the epilayer during fabrication. Here, we developed a robust GaN heteroepitaxy employing a porous buffer layer formulated by hydride vapor phase epitaxy. A sufficiently low but completely coated thin Ti layer was deposited on the sapphire substrate, which led to a rough and porous TiN layer after nitridation. This porous structure enables the penetration of the GaN source into the porous structure, allowing GaN epitaxy initiation throughout the TiN layer. As a result, GaN crystal growth can fill the porous area during the GaN heteroepitaxy. Integrated visualization demonstrated that the voids were successfully removed by GaN infiltration, enabling the heteroepitaxial structure to show little deformation, confirmed by multiple indentations. Last, the void-free GaN heteroepitaxy with the porous TiN buffer layer displayed robust adhesion after delamination tests

Robust Heteroepitaxial Growth of GaN Formulated on Porous TiN Buffer Layers

Gallium nitride (GaN) heteroepitaxial growth is widely studied as a semiconductor material due to its various benefits. Especially, development of a buffer layer between GaN and the substrate verifies to be an effective strategy to reduce high threading dislocation density. However, the buffer layer often impedes strong adhesion between the epilayer and foreign substrate because thermally induced residual stress often causes delamination of the epilayer during fabrication. Here, we developed a robust GaN heteroepitaxy employing a porous buffer layer formulated by hydride vapor phase epitaxy. A sufficiently low but completely coated thin Ti layer was deposited on the sapphire substrate, which led to a rough and porous TiN layer after nitridation. This porous structure enables the penetration of the GaN source into the porous structure, allowing GaN epitaxy initiation throughout the TiN layer. As a result, GaN crystal growth can fill the porous area during the GaN heteroepitaxy. Integrated visualization demonstrated that the voids were successfully removed by GaN infiltration, enabling the heteroepitaxial structure to show little deformation, confirmed by multiple indentations. Last, the void-free GaN heteroepitaxy with the porous TiN buffer layer displayed robust adhesion after delamination tests

Robust Heteroepitaxial Growth of GaN Formulated on Porous TiN Buffer Layers

Gallium nitride (GaN) heteroepitaxial growth is widely studied as a semiconductor material due to its various benefits. Especially, development of a buffer layer between GaN and the substrate verifies to be an effective strategy to reduce high threading dislocation density. However, the buffer layer often impedes strong adhesion between the epilayer and foreign substrate because thermally induced residual stress often causes delamination of the epilayer during fabrication. Here, we developed a robust GaN heteroepitaxy employing a porous buffer layer formulated by hydride vapor phase epitaxy. A sufficiently low but completely coated thin Ti layer was deposited on the sapphire substrate, which led to a rough and porous TiN layer after nitridation. This porous structure enables the penetration of the GaN source into the porous structure, allowing GaN epitaxy initiation throughout the TiN layer. As a result, GaN crystal growth can fill the porous area during the GaN heteroepitaxy. Integrated visualization demonstrated that the voids were successfully removed by GaN infiltration, enabling the heteroepitaxial structure to show little deformation, confirmed by multiple indentations. Last, the void-free GaN heteroepitaxy with the porous TiN buffer layer displayed robust adhesion after delamination tests

Robust Heteroepitaxial Growth of GaN Formulated on Porous TiN Buffer Layers

Gallium nitride (GaN) heteroepitaxial growth is widely studied as a semiconductor material due to its various benefits. Especially, development of a buffer layer between GaN and the substrate verifies to be an effective strategy to reduce high threading dislocation density. However, the buffer layer often impedes strong adhesion between the epilayer and foreign substrate because thermally induced residual stress often causes delamination of the epilayer during fabrication. Here, we developed a robust GaN heteroepitaxy employing a porous buffer layer formulated by hydride vapor phase epitaxy. A sufficiently low but completely coated thin Ti layer was deposited on the sapphire substrate, which led to a rough and porous TiN layer after nitridation. This porous structure enables the penetration of the GaN source into the porous structure, allowing GaN epitaxy initiation throughout the TiN layer. As a result, GaN crystal growth can fill the porous area during the GaN heteroepitaxy. Integrated visualization demonstrated that the voids were successfully removed by GaN infiltration, enabling the heteroepitaxial structure to show little deformation, confirmed by multiple indentations. Last, the void-free GaN heteroepitaxy with the porous TiN buffer layer displayed robust adhesion after delamination tests