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In recent years, perovskite light-emitting diodes (PeLEDs) have developed rapidly with the highest external quantum efficiency exceeding 20%. Their unbalanced carrier injection and non-radiative recombination assisted by defects lead to the destruction of perovskite crystal structures and poor device stability, which hinders their commercialization process. Thus, to understand the origin of device performance, the key is to figure out the charge-carrier dynamics of the devices. In this review, the charge-carrier dynamics of perovskites are discussed, including radiative and non-radiative recombination, together with the various passivation strategies. Second, we focus on the interfacial carrier dynamics and its influence on device performance. Various strategies to improve the injection balance have been implemented to address the inherent challenges associated with PeLEDs. Last but not least, the characterization techniques of PeLEDs are provided to study the carrier dynamics of PeLEDs. [ABSTRACT FROM AUTHOR]

Abstract: A novel cubane-type ZnO (CBE-ZnO) polymorph is studied by means of the first-principles density functional theory calculations. The results suggest that the CBE-ZnO polymorph is mechanically and dynamically stable. The new CBE-ZnO structure is also energetically more favorable than the previously predicted CsCl-ZnO, BCT-ZnO, and the synthesized RS-ZnO polymorphs. The discovery of CBE-ZnO brings about a complete picture of the extent and nature of polymorphism in ZnO family. [Copyright &y& Elsevier]

Abstract: R3ZnH5 (R=K, Rb, Cs) series have been investigated with respect to the crystal structure, electronic and thermodynamic properties using first-principle methods based on density functional theory with generalized gradient approximation. The optimized structures and atomic coordinates are in good agreement with the experimental data. The strong covalent interactions are obtained between Zn and H atoms in the 18-electron [ZnH4]2− complex, while an ionic interaction is found between [ZnH4]2− and R atom. The formation enthalpies show that the formations of R3ZnH5 hydrides are all exothermic at 298K. The vibration free energies of R3ZnH5 show that the thermodynamic stabilities of R3ZnH5 hydrides decrease with the increasing diameter of R atom. Two possible decomposition reactions of R3ZnH5 series have been suggested in our work. One (reaction one) is that R3ZnH5 hydrides decomposes to elements directly, and the other (reaction two) is that R3ZnH5 hydrides decomposes to RH hydride. The results show that the first decomposition reaction is more favorable one. The spontaneous decomposition reaction of K3ZnH5 hydrides occur upon 465K via reaction one, and 564K via reaction two, respectively. [Copyright &y& Elsevier]

Abstract: Nonmetal atoms (B, C and Si) are designed to add into Mg2Ni hydrogen storage alloy and its hydride. First-principles density-functional theory calculations have been performed to investigate their crystal structures, electronic and thermodynamic properties. The calculation results present that nonmetal additions in Mg2NiH4 show more effective destabilization than metal additions. Especially for B and C, the decreases of formation enthalpies of Mg2NiH4 reach 0.19 and 0.21 eV/atom. The NiH4 structure near B or C in Mg2NiH4 hydride becomes the tripod-like NiH3 structure. The results show that the thermodynamic stabilities of Mg2Ni and Mg2NiH4 exhibit a nearly linear decrease with the increasing content of nonmetal atoms. The calculated dehydrogenation energies are 59.39, 58.12, 55.84 and 55.30 kJ/mol H2 for Mg2NiH4, Mg2NiB0.5H4, Mg2NiC0.5H4 and Mg2NiSi0.5H4, respectively. It is found that the addition of nonmetal atoms favors the dehydrogenation reaction for Mg2Ni hydrogen storage material. In addition, the effects of nonmetals to the heat capacities and vibrational entropies of Mg2Ni and Mg2NiH4 are also analyzed. [Copyright &y& Elsevier]

Current–voltage hysteresis of perovskite solar cells (PSCs) has raised the concern of accurate performance measurement in practice. Although various theories have been proposed to elucidate this phenomenon, the origin of hysteresis is still an open question. Herein, the use of guanidinium cation (Gu+)‐dopant is demonstrated to tailor the crystal structure of mixed‐cation formamidinium‐cesium lead triiodide (FA0.83Cs0.17PbI3) perovskite, resulting in an improved energy conversion efficiency and tunable current–voltage hysteresis characteristic in planar solar cells. Particularly, when the concentration of Gu‐dopant for the perovskite film increases, the normal hysteresis initially observed in the pristine PSC is first suppressed with 2%‐Gu‐dopant, then changed to inverted hysteresis with a higher Gu‐dopant. The hysteresis tunability behavior is attributed to the interplay of charge/ion accumulation and recombination at interfaces in the PSC. Furthermore, compared to the cell without Gu+‐dopant, the optimal content of 2% Gu+‐dopant also increases the device efficiency by 14%, reaching over 17% under one sun illumination. A new method to control current–voltage hysteresis of planar structured FA0.83Cs0.17PbI3 perovskite solar cells (PSCs) is presented while enhancing device efficiency through tailoring the crystal structure of the perovskite compound with a guanidinium cation (Gu+)‐dopant. New insights into the correlation of the dynamics of device hysteresis with the interfacial charge recombination and accumulation in the PSCs are revealed. [ABSTRACT FROM AUTHOR]

An advanced architecture design of Bi 2 WO 6 nanoparticles anchored on 3D graphene framework composites as anode material for Li-ion batteries was synthesized by hydrothermal method and sintering. The structure and morphology of the products were characterized by XRD, SEM and TEM. The electrochemical performances of the prepared composites were investigated by galvanostatic charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. Results showed that the first capacity of Bi 2 WO 6 /graphene was 715.2 mAh g −1 at 50 mA g −1 , and it remains as high as 510.1 mAh g −1 after 50 cycles. Moreover, the Bi 2 WO 6 /graphene composites displayed superior rate capability. All tests proved that the Bi 2 WO 6 /graphene oxide composites showed excellent electrochemical properties. [ABSTRACT FROM AUTHOR]

Abstract: The graphite fragments are used to establish the calculated models of LiBH4 mechanically milled by graphite additive. Density-functional theory calculations have been performed to optimize the crystal structures of LiBH4 inserted by different graphite fragments. It is found that the unsaturated sites introduced by graphite fragments are occupied by BH3 complexes and H atoms. The dehydrogenation energies are calculated to investigate the dehydrogenation ability of LiBH4 with graphite fragments. The results show that BH3 complexes bonded with graphite fragments have lower dehydrogenation energy than pure LiBH4, which is an important factor of the improvement of thermodynamic property of LiBH4 system. The hydrogen diffusion behaviors of graphite fragments doped LiBH4 are investigated by the nudged elastic band method. It is found that the hydrogen diffusion barriers of β-H (the H atoms of BH3 complexes bonding with C atoms) diffusing to other sites are small in the LiBH4/graphite fragment systems. The results show that the existence of β-H type significantly enhances the hydrogen diffusion kinetics of the graphite fragments doped LiBH4. [Copyright &y& Elsevier]