The Application Of Thin Films And Metal Nanoparticles On Water Splitting Solar Cells

With the rapid development of moderm industrialization,People,s demand for energy is getting higher and higxer.The burning of traditional fossil fuels will release a large number of harmful gases,causing serious pollution to the environment.Therefore,environmental pollution and energy crisis become the two major issues that humans will face in the twenty-first century,and that it's very urgent to solve.To solve these problems,it's imperative to find renewable and clean energy sources.Although solar is the most abundant renewable energy on earth,it,s not easy to store.Sunlight can be used to split water into hydrogen,producing chemical energy stored in hydrogen bonds.This easy way of producing clean fuels(hydrogen)has attracted the attention of both industry and academy.In this thesis,we design and characterize photoanodes and photocathodes for water splitting solar cells.The samples have been fabricated and analyzed using different techniques with nanometer resolution,and their performance is reported.We focus on the research of photoanode materials for water splitting solar cells.Metal catalysts are used to enhance the activity of the photoelectrodes,which has arrived to acceptable current densities(?ma·cm-2).However,the lifetime of the photoanodes is still a problem.In the first part of this thesis,we coated thin nickel films(2 nm 5 nm and 10 nm)on the surface of n-type silicon wafers to measure their photoelectrochemical activity and stability as water-splitting photoanode in the alkaline solutions with different pH.The ageing mechanisms of Ni/SiOx/n-Si photoelectrodes under the light-driven oxygen evolution reaction(OER)are comprehensively analyzed at nano and atomic scales.At pH 14,the ageing mechanisms rely on the thickness of the Ni coating layer;at pH 9.5,the existence of Li+ significantly improved the stability of the photoanodes,but the form of deposition layer on the surface made the sample decay.It is worth nothing that,in this work,we for the first time introduced the use of electron energy loss spectroscopy(EELS)on the study of water splitting solar cells,and also demonstrated that traditional equipment(e.g.XPS)may ignore some important information on the reseach of water splitting solar cells.These results could be useful for understanding the degradation and enhancing the yield of water splitting solar cells.In the second part,we study the photocathode part,which consisted on n-type 3C-SiC wafers dercorated with metal nanoparticles.The idea is to exploit the strong chemical stability of 3 C-SiC as the protective layer and emitter coated on the p-type silicon surface.The role of the noble metal nanoparticles(Au or Pt,deposited following different approaches)on the surface of SiC is to enhance the overall activity.The data collected suggest that,under suitable conditions of metal nanoparticles deposition,the onset potential is considerably reduced due to the catalytic effect,and the plasmonic resonance effect will increase the photocurrent of the photocanode.Optical and micro-structural studies on the nanoparticles provide insights on the origin of the observed effects.