Controllable Fabrication And Photoelectrochemical Properties Of Order Silicon Microwire Arrays

Recently,Si micro-/nanowires have attracted much attention because of their excellent physical and chemical properties.Relativeto silicon nanowire arrays（SiNWAs）,Silicon microwire arrays（SiMWAs）havecomparable performances oflight absorption and high photo-generatedcarrier collection efficiencyfor constructing high-efficiency,low-cost and stable solar cell.Furthermore,largespacing and controllablemorphologyof Si MWAs are benefit for the permeating of coatingmaterials to form heterojunction,which is significant to enhance the photoelectric-conversionefficiency.However,numerous works still should be investigated on the fabrication of wafer scale,large spacing and high-aspect-ratio SiMWAs and theconstruction of double absorption layer with surface modification/passivation to further improve thephotoelectricproperty of Si micro/nanostructure-based devices.In this work,we prepared orderly morphology SiMWAs with metal-assisted chemical etching（MACE）method and studied the migration of metal catalyst and chemical etching mechanism.Then,weconstructed SiMWAphotoelecrochemical（PEC）cell withmetal nanoparticles surface modification and metal oxide surface passivation,and investigated their photoelectrochemical properties.Finally,we grow hematite（?-Fe₂O₃）film on SiMWAs and SiNWAs to investigate the double absorbersystem for water splitting.The main conclusions in this thesisare as following:1.We controllably fabricatedorderlySiMWAs with optimized etching conditions,shed light onthe influences of metal catalyst species,thickness,etching time,etching temperature and etchant concentration.It shows that lower temperature and higher etchant concentration are benefited for sustaining the migration of metal catalyst and etching thehigh-aspect-ratio SiMWAs.This method has advantages of easier operation,low cost and controllable.The obtained large-spacing and high-aspect-ratio Si MWAs can be used tostructureorganic/inorganichybridsolarcell,andimprovethe photoelectric-conversion-efficiency of devices.2.Based on the SiMWAs,we constructed Si MWA electrode modified with Pt nanoparticles and passivated with TiO₂ film（TiO₂/Pt@SiMWAs）,and investigated their photoelectrochemical performance.Experimental results show that photoelectrochemical response and performance stability ofTiO₂/Pt@SiMWAs electrode are significantly improved through Pt nanoparticles surface modification and TiO₂ultrathin film surface passivation.The saturated photocurrent density(J_sc)of electrode was improved³0%,and the attenuation degree of J_sc was decreased from⁸8%to¹.5%.3.We fabricated hematite filmon SiNWAs,andstudiedthe PEC properties for solar water splitting.Compared to SiNWAs,?-Fe₂O₃/SiNWAs electrode showshigher photocurrent density.Sndoping into?-Fe₂O₃can improve theefficiency of photo-carrier collection.Furthermore,the PEC test with adding hole scavenger（H₂O₂）into electrolyte shows that the photocurrent density was firstly increased and then decreased,demonstratingthe serious surface recombination of photoanode.So the following endeavor is needed for obtaining the high-quality?-Fe₂O₃.