Electrical transport properties of TiO2/MAPbI3 and SnO2/MAPbI3 heterojunction interfaces under high pressure.

The electrical transport properties of SnO2(TiO2)/MAPbI3 (MA = CH3NH3 +) heterojunction interfaces are investigated from ambient pressure to 20 GPa, and the transport properties are calculated by physical parameters such as trap energy density, binding energy, and charge transfer driving force and defect. Based on the partial density of states (PDOS) of the SnO2/MAPbI3 heterojunction interface MAI-termination and PbI2-termination, greater charge transfer driving force and higher binding energy are observed, obviously showing the SnO2-based heterojunction is more stable. The SnO2/MAPbI3 heterojunction interface possesses stronger electrical transport ability and is less prone to capture electrons compared with the TiO2/MAPbI3 heterojunction interface. The differential charge density spectrum shows that the density is lower in the trap energy level of SnO2/MAPbI3, whilst the effect of the charge transfer defect is weaker owing to the trap energy level only existing in SnO2. The SnO2/MAPbI3 heterostructure interface is less prone to capture electrons. The greater electron concentration difference is attributed to oxygen vacancy (Vo0) in the SnO-like environment, resulting in superior electron transport ability compared with the TiO-like environment.

Synthesis and high-pressure transformation of metastable wurtzite-structured CuGaS2 nanocrystals.

The metastable wurtzite nanocrystals of CuGaS(2) have been synthesized through a facile and effective one-pot solvothermal approach. Through the Rietveld refinement on experimental X-ray diffraction patterns, we have unambiguously determined the structural parameters and the disordered nature of this wurtzite phase. The metastability of wurtzite structure with respect to the stable chalcopyrite structure was testified by a precise theoretical total energy calculation. Subsequent high-pressure experiments were performed to establish the isothermal phase stability of this wurtzite phase in the pressure range of 0-15.9 GPa, above which another disordered rock salt phase crystallized and remained stable up to 30.3 GPa, the highest pressure studied. Upon release of pressure, the sample was irreversible and intriguingly converted into the energetically more favorable and ordered chalcopyrite structure as revealed by the synchrotron X-ray diffraction and the high-resolution transmission electron microscopic measurements. The observed phase transitions were rationalized by first-principles calculations. The current research surely establishes a novel phase transition sequence of disorder → disorder → order, where pressure has played a significant role in effectively tuning stabilities of these different phases.

ZnS nanocrystals and nanoflowers synthesized by a green chemistry approach: rare excitonic photoluminescence achieved by the tunable molar ratio of precursors.

In the present work, we demonstrated a simple and green synthesis route for shape-controlled ZnS nanocrystals, where only environmentally benign chemicals, namely sulfur, zinc oxide and olive oil, were employed. By controlling the experimental conditions, we were able to tune the band edge and trap state photoluminescences of ZnS nanocrystals and obtain pure excitonic photoluminescence that was rarely observed in literature. The trap state emission was derived from sulfur vacancies and would be eliminated when an excess of sulfur was used during the synthesis. Additionally, the morphology of ZnS nanocrystals could be tuned to appear like flowers, where the formation mechanism was systematically discussed.

Facile synthesis of tin oxide nanoflowers: a potential high-capacity lithium-ion-storage material.

A facile and reproducible approach was reported to synthesize nanoparticle-attached SnO nanoflowers via decomposition of an intermediate product Sn6O4(OH)4. Sn6O4(OH)4 formed after introducing water into the traditional nonaqueous reaction, and then decomposed to SnO nanoflowers with the help of free metal cations, such as Sn2+, Fe2+, and Mn2+. This free cation-induced formation process was found independent of the nature of the surface ligand. It was demonstrated further that the as-prepared SnO nanoflowers could be utilized as good anode materials for lithium ion rechargeable batteries with a high capacity of around 800 mA h g(-1), close to the theoretical value (875 mA h g(-1)).