Fabrication Of Ⅱ-Ⅵ Group Semiconductor Materials And Their Application In Organic Photovoltaic Devices

Due to the energy crisis and environmental problems, the demand for renewableclean energy is more and more urgent in recent years. Solar energy is inexhaustible andclean. As a new energy without any pollution, it is being developed and utilizedquickly all over the world. And it is thought as the substitution of coal, oil, natural gasand other non-renewable energy sources.Solar cells contain crystalline silicon solar cell, amorphous silicon solar cell, III-Vcompound solar cell, CIGS (CuInGaSn) thin film solar cell, dye sensitized solar cells,organic solar cells (or organic photovoltaic) and so on. Organic photovoltaic device(OPV) is one of the most popular and attractive technologies, which is low cost, easyprocessing of large-area fabrication, and compatibility with flexible substrates.The function mechanism of the OPV can be described as following: the excitons,which were in excited states after the light radiation, transfer between donor (p-type)and acceptor (n-type); then the excitons are separated into electrons and holes; thesefree charge carriers pass through the bulk layer and are collected by the electrodes;finally photo-induced voltage is generated. Photocurrent will also be provided in theexternal circuit.In order to improve the power conversion efficiency of these organic photovoltaicdevice, the electron transport layer and the hole transport layer are often insertedbetween the active layer (including the donor material and the acceptor material) andthe electrodes, to enhance the efficiency of excitons separation.In this thesis, the synthesis of II-VI semiconductor materials through a variety ofphysical and chemical methods are introduced, and their application in organicphotovoltaic devices is presented. The properties of these materials, such as Ⅱmorphology, optical properties, electrical properties, surface energy and electronicenergy levels, are charaterized. Besides that, the working mechanism of organicphotovoltaic devices incorporating II-VI semiconductor materials is invesigated.The followings are included in this thesis:(1) Using the high-temperature furnace to thermal vapor deposit nano materials.The regular nano-arrays have potential advantages in the fabrication of photovoltaicdevices. Due to the excellent properties of cadmium sulfide (CdS), CdS nano-arrays issynthesized by adjusting the reaction pressure, deposition location and heatingtemperature. The mechanism is studied.(2) Chemical bath deposited CdS film and fabricate organic photovoltaic devices.The thickness and morphology of CdS film was adjusted by varying the bathtemperature, immersing time and annealing treatments. Compared with the propertiesof devices and film, an in-depth study of the working mechanism is carried out.(3) Organic photovoltaic devices with atomic layer deposited CdS film as anelectron election layer are introduced. The processing of atomic layer deposition couldobtain high quality CdS film, and the thickness could be controlled accurately. Thethickness, morphology, crystal structure, surface energy and electronic energy levelswere characterized with Ellipsometer/AFM/TEM/contact angle measurementsystem/XPS. A comprehensive understanding of the materials will be benefited forresearch. Selecting the CdS film as an electron collection layer can reduce the workfunction of ITO, so that the energy level matching between the ITO and thephotoactive layer. It can effectively improve the excitons dissociation efficiency oforganic photovoltaic devices. The power conversion efficiency reaches to3.33%.