Two-Dimentional Nanomaterials: Synthesis And Optoelectronic Performance Study

Two-dimensional (2D) nanomaterials have large surface area and distint interlayer and intralayer interactions and the consequent novel and attractive properties, which enable them potential application in electronics, optoelectronics, catalysis, and sensing. Moreover, the two-dimensional morphology is beneficial fordevice fabrication including lithography and electrode preparation, and hence is advantageous for the manufactering of optoelectronic devices requiring large area, high quality and high performance. However, most of the 2D nanomaterials synthesis strategies reported so far are limited to layered compound and there are sparse reports regarding the synthesis of nanosheets of non-layered compound. Therefore, it will be meaningful to expand the study scope to the materials with non-layered structure, which will not only expand the family of 2D nanomaterials, but also promise new device performances.In this thesis, by considering the inherent properties of two-dimensional nanomaterials, combined with a careful analysis of the advantages and disadvantages of various preparation methods, we demonstrated two new synthetic strategies. Both strategies were general, simple, efficient and green, thus providing new ideas and approaches for preparing 2D nanomaterials, especially the ultrathin 2D nanomaterial. Subsequently, an application-oriented development of 2D nanaomaterials was implemented, aiming at exploiting their application in different fields.The main content of this thesis is summaried briefly as follows:(1) We have first demonstrated a lattice matching induced nanosheet growth strategy to synthesize metal chalcogenide nanosheets from various materials possessing different crystal structures. Through this strategy, Sb2S3, Sb2Se3, ZnS, MoS2 and WS2 nanosheets with micrometer size and atomic thickness were successfully fabricated using NaCl and KC1 salts as the synthetic templates. According to the crystal structural model and the results of HRTEM and SAED, the lattice matching between the substrates and the target materials could promote the film growth onto the template, and concurrently suppress their natural growth tendency into one-dimensional or three-dimensional nanostructures. Subsequently, considering the strong visible absorption of Sb2S3 nanosheet, we fabricated a flexible photoconductive photodetectors, of which the mixture of Sb2S3 nanosheet and poly(3-hexylthiophene) (P3HT) was the active material, ployimide was substrate. After repetitive bending, the device still showed sensitive photoresponse.(2) Expanded the lattice matching induced nanosheet growth strategy to the preparation of 2D metal oxides with non-layered strutures, and then various 2D metal oxides with high crystallinity and large size were successfully synthesized. As-obtained 2D MoO3 and WO3 nanosheets were applied to supercapacitors, and the outstanding performance implied their application prospect in the field of energy storage. The highest volumetric and gravimetric specific capacitance was as high as 600 F/cm3 for MoO3 nanosheets and 350 F/g for WO3 nanosheets, respectively, under the sweep rate of 5 mV/s. The fast and reversible capacitive storage process was benefit from the rapid ion diffusion in the interlayers and the fast electron transport within the individual nanosheets.(3) We demonstrated a new freezing-thrawing approach for preparing ultrathin and large-sized Sb2Se3 nanosheets with 1D ribboned structure. XRD was employed to investigate the formation mechnism of 2D Sb2Se3 nanosheet. Subsequently, to explore the optoelectronic properties of the Sb2Se3 nanosheets, ultrathin Sb2Se3 nanosheets-based photodetectors were fabricated. Remarkable optoelectronic performance was acquired. Finally, the strong optical anisotropic nature of Sb2Se3 nanosheet was demonstrated experimently by means of polarized Raman spectra.(4) We fabricated and investiaged the photovoltaic performance using layered Bi2S3 as light absorption layer. Firstly, compact Bi2S3 films with high crystallinity and few defects was fabricated using a rapid thermal evaporation (RTE) process. Then, the optimal process was achieved by optimizing the set temperature of substrate and source, as well as by adding a post-annealing step. Subsequently, XRD, XPS, SEM, UV-Vis absorption spectra, PL spectra and Hall measurements were employed to characterize as-obtained film. Finally, ITO/NiO/Bi2S3/Au solar cells were fabricated using B12S3 as light adsorption layer. Tests showed that its open circuit voltage, short circuit current density, fill factor and preliminary power conversion efficiency was 0.23 V,10.0 mA/cm2,0.33 and 0.75%, respectively.