The Synthesis And Application Of Layered Group-â…¥ Metal Chalcogenides

Graphene-like layered group-Ⅵ metal chalcogenides, which is constituted of a monolayer or few layers, is a new two-dimensional (2D) layered material which owns excellent electrical, optical and catalytical properties and can be widely used in electronic devices, energy storage, hydrogen evolution and other fields. When the 2-D layered group-Ⅲ metal chalcogenides downsize to quantum dots which is 0 dimensional, can manifest surface effect, small size effect, interficial effect and macroscopic quantum effect. MoS2 and WS2 quantum dots, have recently attracted considerable attention as they own unique properties. We sythesized monolayer WS2 nanoplates through Li-intercalation exfoliation method and applied it as the hole transport layer in organic solar cells. This essay was also focused on the synthesis of MoSe2 quantum dots as well as their luminenscence property and mechanism.In chapter 1, we introduced the conception and basic properties of 2D layered group-Ⅵ metal chalcogenides and quantum dots. Then we reviewed the synthesis methods and application of them.In chapter 2, we sythesized monolayer WS2 nanoplates aqueous solution with good film-forming properties through Li-intercalation exfoliation method and explored the performance of both the chemically exfoliated WS2 and UV-ozone treated WS2 as the hole extraction layer in organic solar cells based on PTB7/PC71BM. The results showed that after UV-ozone treatment the power conversion efficiency (PCE) had been greatly improved to 8.37%, which is comparable to the OSCs with the standard PEDOT:PSS as the HEL. We attribute the improvement to the incorporation of oxygen into the lattice of the WS2 sheets. The oxygen incoporation reduces the vacancies of WS2 sheets and makes the WS2 partially oxidize and consequently improve the electrical properties of the WS2 sheets.In Chapter 3, we synthesized MoSe2 QDs with good size homogeneity and dispersity via liquid sonication exfoliation method, and changed the size of MoSe2 QDs through adjusting the reaction parameters, such as solution, utrasonic power. We further studied the the luminenscence mechanism and the influence of the QDs size, surfacant on luminenscence. The characterization results showed that the MoSe2 have two emissions, the UV emission which is intrinsic and the visible emission which is related with the surface defects. The influence on the MoSe2 luminenscence varied within different kinds of surfacant. The anionic surfacant can improve the visible emission intensity while had rarely effects on the UV emission. And when the size of MoSe2 QDs decreased, the ratio of the visible emission intensity to the UV emission intensity increased as well as the fluorescent lifetime increased. The reason is that the QDs’ specific surface area increases as the QDs’ size decreases, resulting in more surface defects thus the electron will be trapped for a longer time.