Research on Photoelectric Properties of Metal Nanoparticles Modified TiO2-based Photoelectrochemical Photovoltaic Cells

Author:Huang Yue Wu

Supervisor:wang jin zhong


Degree Year:2019





Energy is an important material guarantee for the survival and development of human society and the basis for national economic and social development.With the depletion of fossil energy and the global concern for the greenhouse effect,the development and utilization of clean renewable energy is becoming the main theme of the current and future world energy technology development.Photoelectrochemical photovoltaic cells can convert light energy into electrical energy,which can effectively solve energy and environmental pollution problems,mainly including dye-sensitized solar cells(DSCs)and photoelectrochemical ultraviolet detectors(PEC UVPDs).The photoelectric conversion efficiency of photoelectrochemical photovoltaic cells depends closely on the light harvesting capacities of the photoanodes,the transport of photogenerated electrons through the semiconductor electrode,and the dynamics of interfacial losses resulting from the interface in the cells.In a traditional nanocrystalline TiO2 electrode film,the TiO2nanoparticles are not densely packed,therefore the length of the electron path to the conducting substrate is longer,increasing the chance of interfacial losses.At the same time,this photoanode exhibits negligible light scattering capability,resulting in relatively poor light harvesting efficiency In view of the above constraints,focusing on how to improve the power conversion efficiency of photoelectrochemical photovoltaic cells,we have studied the structure optimization and modification of TiO2 photoanode.The detailed contents are listed as following:TiO2 mesoporous spheres with high crystallinity and large specific surface area were facilely prepared via sol-gel and solvothermal methods.By tuning the time and temperature of the solvothermal process,the specific surface area and pore size of TiO2 spheres were fine-controlled.UV-visible absorption spectroscopy,electrochemical impedance spectroscopy and photovoltaic test results show that TiO2 mesoporous spheres have high dye loading,excellent light scattering properties,and can effectively inhibit electron recombination at the TiO2 mesoporous/dye/electrolyte interface.The dye-sensitized solar cell employing TiO2 mesoporous spheres achieves an excellent efficiency of 10.3%.In addition,combined with the lowvolatility MPN-based electrolyte,it is for the first time demonstrated that the>10%DSC based on a single-layer TiO2 film can retain a rather good long-term durability.Au@Ag@SiO2 core-shell nanorods were prepared by solvothermal method and incorporated into TiO2 mesoporous spheres photoanode to assemble DSCs.Light harvesting of dyes is enhanced by the localized surface plasmon resonance(LSPR)effect of metal nanostructures.At the same time,the introduction of Au@Ag@SiO 2nanorods can effectively compensate for the insufficient light absorption of C106dye in the near-infrared region and further improve the light harvesting of the devices.Based on this,the short-circuit current density of the device increased from17.38 mA cm-2 to 19.28 mA cm-2,and the power conversion efficiency reached11.3%.To verify the effect of LSPR on DSCs,we used time-domain finite difference method(FDTD)and transient absorption spectroscopy(TAS)to analyze the plasmon enhancement mechanism of the devices.The FDTD results show that the enhanced electromagnetic near field around Au@Ag nanorods increases its interaction with the dye molecule dipole,which is beneficial to improve the light harvesting of the dye.The TAS results show that LSPR-induced plasmon resonance energy transfer(PRET)can effectively increase the light harvesting of dyes in DSC,increase the generation of electron-hole pairs in the dye molecules,and thus increase the electron injection into the conduction band of TiO2.The SnO2 mesoporous sphere were prepared by hydrothermal method and coated with TiO2 shell on the surface to prepare mesoporous spherical SnO2@TiO2core-shell heterojunction photoanode.This electrode provides a highly efficient electrode structure model for PEC UVPD.In the SnO2@TiO2 core-shell structure,the different electron affinity between the two semiconductor causes the isoelectric point of TiO2 to be higher than that of SnO2,yielding a surface dipole layer toward SnO2.This surface dipole layer can effectively suppress the transmission of electrons from SnO2 to TiO2 and reduce the recombination loss of carriers,thereby,the response time of the device isτr=0.007 s,τd=0.006 s,and the on/off ratio reaches Jon/Joff(28)11519.In addition,SnO2@TiO2 mesoporous spheres/Ag@TiO2nanoparticles composite film was prepared by self-assembly method,and as the photoanode of PEC UVPD,the local surface plasmon resonance effect of Ag@TiO2nanoparticles was used to further improve the photoelectric conversion performance of the PEC UVPDs.As a result,the short-circuit current density and open circuit voltage of PEC UVPD increase to 4.44 mA cm-2 and 433 mV,the responsivity reaches 0.132 A W-1.PEC UVPDs assembled by using Ag@SiO2 core-shell nanoparticles modifying TiO2 nanocubes as photoanodes.The incorporation of plasmonic Ag@SiO2core-shell NPs can effectively enhance the light harvesting efficiency of photoanodes.By optimizing the incorporation ratio of Ag@SiO2 nanoparticles,the response time of PEC UVPD(2 wt%Ag@SiO2 nanoparticles)reachesτr=0.003 s,τd=0.008 s,and the responsivity reaches 0.151 A W-1.Finite difference time domain(FDTD)and transient absorption spectroscopy(TAS)were employed to analyse the effects of localized surface plasmon resonance of Ag nanoparticles on the photoelectric conversion performance of the devices.