Solvothermal Preparation Of Transition Metal Selenide Films And Their Application In Photoelectric Devices

Transition metal dichalcogenides（TMDs）are an important class of semiconductor materials.They have narrow band gap,high carrier mobility and light absorption over a wide wavelength range,making it a candidate for high-performance optoelectronic devices.Compared with methods such as chemical vapor deposition and mechanical stripping,solution-based synthesis methods including hydrothermal and solvothermal methods,are low-cost and facile to produce large-area,uniform and stable films.However,most of the selenides prepared by solution-based methods are powder types,and subsequent film formation by spin coating is required to fabricate optoelectronic devices.The direct solution synthesis of transition metal selenide film can produce large-area,high-quality thin film materials with simplified device fabrication process,which are of concern to researchers.In this thesis,we studied the preparation of transition metal selenide films on different substrates by solvothermal method.We used the prepared selenide to develop a photodetector with good performance.We also studied the application of metal selenide films as the counter electrode in dye-sensitized solar cell.The main contents of the study are as follows:1.The uniform and stable WSe₂ film with good quality was directly prepared on the FTO and quartz substrate by solvothermal method.The prepared WSe₂ films are composed of dense layered nanosheets.The thickness of the film on the FTO is about700 nm and the thickness of the nanosheet is 10 nm.The thickness of the film on the quartz is about 1.2μm and the thickness of the nanosheet is 20 nm.In addition,the WSe₂ nanoflowers were directly grown on three-dimensional graphene film by solvothermal method to form the WSe₂/rGO composite film.2.The growth mechanism of WSe₂ film was analyzed.The effects of deionized water volumes,synthesis temperature and reaction time on the structure and morphology of WSe₂ film were studied.It was found that deionized water plays an important role in the growth of the film,but the volumes of deionized water does not have a significant effect on the structure and morphology of the film.The synthesis temperature has a great influence on the growth of the film.As the react temperature increased,the film thickness is obviously increased.Also,the compactness and crystallinity of the film are gradually enhanced with the increasing of temperature.The reaction time also has influence on the growth of the film as the film thickness increases slowly with the increase of the reaction time.3.The photoresponse performance of photodetector based on WSe₂ films prepared on the quartz were tested.The response time of the device was 0.16s and the photosensitivity was 3.3 mA/W under the illumination of 532 nm laser.The photosensitivity is 5.8 mA/W and the response time is 0.7s under the illumination of405 nm laser.Compared with other reported TMDs photodetectors based on solution method,the WSe₂ photodetector in our work exhibited superior performance.4.MoSe₂ films were prepared on the FTO and the quartz by solvothermal method.The MoSe₂ film on FTO is uniform and dense with smooth surface.The MoSe₂ film on the quartz consists of many layered nanosheets.The thickness of the nanosheet is about 40 nm.Phase analysis shown that the MoSe₂ film is in hexagonal structure and has good crystallinity.5.The WSe₂ film and the WSe₂/rGO composite film prepared on the FTO were used as the counter electrode for dye-sensitized solar cells and obtained power conversion efficiency of 1.69%and 3.09%,respectively,which was less than that of7.37%for Pt counter electrode device.The MoSe₂ film was also used as a counter electrode for dye-sensitized solar cell and obtained the PCE of 2.4%,which was also less than that of 7.14%for the Pt counter electrode device.