Interface-Rich Semiconductor Heterojunctions Based On Sub-Nanoscale Chalcogenide Clusters And Their Optical And Photoelectric Properties

For the past few years,synthetic chemical researchers have devoted into constructing the high performance photoelectric materials for conquering global energy and environmental risks facing today.Semiconducting chalcogenides have been proved to be an effective functional material to be applied to solar conversion due to their suitable bandgap and band potential.Therefore,the synthesis and design of chalcogenide based photoelectric materials have gradually become the focus of researchers for solar energy utilization,and considerable achievements have been made up to now.However,the development of chalcogenide materials are facing bottlenecks of pursuing higher performance and exploring of explicit dynamics and thermodynamics due to the limitation coming from structural aspects.Cluster-based crystalline chalcogenide inspired by zeolite oxides have drawn great attention on account of their integration of unique structural(including ultrasmall clusters with diversity packing modes,multi-metal co-doping,precise atom location,porosity,dispersibility and so on)and semiconducting features.This kind of semiconducting chalcogenide with high degree of designability not only provides a design platform for the construction of high-performance optoelectronic materials,but also provides a material basis for deeper understanding charge transfer kinetics in photoelectric or photocatalytic applications.This thesis takes discrete chalcogenide clusters and cluster-based frameworks as research objects,with the purpose of constructing novel interface-rich semiconductor photoelectric material system of chalcogenide cluster-based semiconducting heterojunction,to explore explicit structure-function relationship in solar energy conversion applications.Such cluster-to-heterojunction strategy provides new synthetic entryway into building other superior photoelectric materials.The research contents mainly focus on the following aspects:1.Light-Triggered Evolution of Molecular Cluster toward Sub-nanoscale Heterojunction with High Interface Density:We report a simple,yet highly effective approach in constructing a new type of sub-nanoscale ZnS/ZnO heterojunction with highly-rich interfaces by photoetching hybrid Zn-S-O molecular clusters.The obtained spherical nanoparticles(～2-4 nm)with sub-nanoscale"parasitical" interface structure and high interface density displays superior separation efficiency of electron-hole pairs,compared to nanoscale homologous series with low interface density obtained via conventional heat treatment,which was demonstrated by photoelectric and photocatalytic measurements.Such light-triggered molecular-cluster-to-heterojunction strategy provides synthetic entryway into building other sub-nanoscale hetero-structured materials for further promoting the catalytic-related applications2.Direct Observation of Charge Transfer between Molecular Heterojunctions Based on Inorganic Semiconductor Clusters:We reveal the dynamics of charge transfer between inorganic semiconductor molecular heteroclusters by selecting a group of open-framework metal chalcogenides as unique structure models constructed from supertetrahedral T3-InS([In10S20])and T4-MInS([M4In16S35],M=Mn or Fe)clusters.The staggered band gap alignment in T3-T4-MInS molecular heterojunctions enables the photogenerated charge carriers to be directionally transferred from T3-InS clusters to adjacent T4-MInS clusters upon irradiation or application of an external electric field.The simultaneous independence of and interactions between such two heteroclusters are investigated by theoretical calculations,steady-and transient-state absorption/photoluminescence spectroscopy,and surface photovoltage analysis.Moreover,the dynamics of cluster-to-cluster-to-dopant photogenerated charge transfer is deliberately elucidated.Thus,this work demonstrates the direct observation of charge transfer between molecular heterojunctions based on purely inorganic semiconductor clusters and is expected to promote the development of cluster-based semiconductors for solar cells.3.Construction of In-Se Semiconducting Frameworks by Using Heteroclusters and Exploring Their Photocatalytic Performance:Developing the structural diversity of microporous zeolitic frame-works with the integrated semiconducting properties is promising,but remain a challenge.Reported here are two unique crystalline semiconductor zeolite analogues constructed from two kinds of In-Se clusters with the augmented ctn net and zeolite-type sod net,respectively.The intrinsic semiconducting nature in these In-Se domains gives rise to pore-size-dependent and visible-light-driven photocatalytic activity for organic dye degradation.4.Synthesis of Open Chalcogenide Semiconducting Frameworks that Built from Unusual Subunits:Incorporation of novel subunits(nodes and linkers)into superlattice is of great significance for enriching chalcogenide frameworks and conquering interpenetration of multiple networks.In this chapter,we obtained four new open chalcogenide frameworks though solvothermal synthesis.All of these structures are constructed by unconventional bridging units,such as the polyselenide units and metal-selenide rings.In particular,compound 4 constructed by new super tetrahedral cluster and diverse bridging units shows impressive structure and ultra-high porosity,suggesting the important role of subunits.UV-Vis absorption analysis indicate that these In-Se frameworks retain semiconductor properties,making them potential candidates in photocatalytic applications.