Synthesis And Application Of The Arrays Of BiOI Nanoflakes

Global energy issues became apparent due to the Oil Crisis in 1973, which led to a universal awareness of the scarcity of fossil fuels. A few years later, many governments (United States, Japan, Germany, etc.) began to explore new alternative energy sources and technologies. Solar energy attracted much attention because it used the abundant light from the sun, and did not produce pollution. However, solar energy contributed little to everyday energy consumption because of the current high cost of the silicon solar panels. Among these solar cells, TiO2 Dye-Sensitized Solar Cells (DSSCs) provided a promising solution for the low-cost solar power conversion. In addition, based on the study of DSSCs, people developed a series of new solar cell materials and cell assembly technologies.BiOI was found to have photovoltaic response in 1985. In order to enhance its photovoltaic response, sensitization with rhodamine B or electrooxidation of a pre-loaded bismuth film were used to expand the adsorption wavelength range and accelerate the electron transfer of the BiOI photoelectrodes for the conversion of solar energy. However, the photocurrents of all these reported BiOI solar cell were as low as tens of microamps, largely limiting its applications. Recently, we constructed a BiOI-chitosan solar cell by coating the mixture of BiOI nanoplate microspheres and chitosan on ITO glass electrode, where the chitosan acts as the glue to bind the BiOI. However, the photovoltaic efficiency of BiOI-chitosan solar cell was not ideal for the poor electronic conduction between the BiOI microspheres and chitosan. To solve this problem, it is of great importance to develop a method to realize the direct growth of BiOI on the electrode, which would achieve higher photoelectroical efficiency through the direct electronic transport from BiOI to the electrode.Successive ionic layer adsorption and reaction (SILAR) is a thin film construction technology and is also known as a modified method of chemical bath deposition (CBD). This process involves the dipping of substrate into several solutions in turn with different deposition cycles to produce thin film with a controllable thickness from nanometers to micrometers. Moreover, it could be performed only at or close to room temperature, atmospheric pressure, and small amount of precursors, very suitable for many unstable substrates and a variety of film materials.This dissertation mainly introduces the energy problem and the meaningful research of the solar cells and then focuses on the technology of the SILAR method to form crossed like BiOI nanoflake arrays on different substrates, such as FTO glass and flexible ITO/PET membrane. We evaluated the photovoltaic properties of the BiOI nanoflake arrays and used the properties to develop a new type of photoelectrical biosensor. We tested the photovoltaic properties of the BiOI thin film solar cells and combined the thin film electrode with biosensor to build photoelectrical biosensor. The new type photoelectrical biosensor had good sensitivity and detection limit.1.The BiOI nanoflake arrays were directly grown on FTO substrate by SILAR method. The resulting BiOI nanoflake arrays solar cell (15 cycles'SILAR) could exhibit Jsc of 241 uA cm-2, Voc of 0.62 V, FF of 0.61,ηof 0.092%, and maximum IPCE of 4%. This work provides an attractive and new solar cell system and a facile route to fabricate low cost and non-toxic solar cell.2. The BiOI nanoflake arrays were fabricated on flexible ITO/PET substrate by SILAR method. The BiOI/ITO/PET electrode build with 30 cycles' SILAR at room temperature has the highest photocurrent with Jsc of 529μA cm-2, Voc of 0.55 V, FF of 0.55,ηof 0.132%, and maximum IPCE of 6.5%. Although the photocurrent of the flexible BiOI/ITO/PET solar cells is still low compared to other applied solar cells, its photovoltaic performance is higher than the BiOI/FTO electrode. Though it is build without TiO2 block layer, the FF of the BiOI/ITO/PET electrode is higher than 0.5 due to the increasing thickness of the BiOI nanoflake arrays. We believe the performance of the BiOI solar cell could further improved through dye sensitization for solar energy utilization in the future.3. The HRP/BiOI/FTO electrode was fabricated by immersed the BiOI/FTO electrode in horseradish peroxide (HRP) solution to adsorb the enzyme. The HRP/BiOI/FTO electrode exhibit excellent biological activity, indicating that the crossed BiOI flake arrays have no harmful effects with the HRP, and are suit for immobilizing enzyme with good biological compatibility. During the detection process of H2O2, the HRP/BiOI/FTO electrode performs a linear relationship between the photocurrent and the concentration of H2O2 in the range of 10～70 and 90～250μM. The detection current is about 9μA, more higher than the common biosensors. The HRP/BiOI/FTO electrode is a so good photoelectrical biosensor that we will immobilize other enzymes to increase the range of applications of the electrode.4. Graphene was synthesized by reducing the graphene oxide with hydrazine hydrate. The graphene paper prepared by adsorption of graphene oxide and subsequent reduction had best performance in the resistance test. The resistance of the graphene paper was 9-23 kQ. And then we build BiOI nanoflake arrays by successive ionic layer adsorption and reaction method on the graphene paper. The flexible BiOI/graphene/filter paper exhibited photovoltaic performance and could be used for further application.