Band Modulation Of TiO₂ And Its Application In Quantum Dot-sensitized Solar Cells

Currently,people have always been committing to find the best alternatives to nonrenewable energy sources such as coal,oil and natural gas.As one of the most promising devices in the third generation of solar cells,quantum dots sensitized solar cells(QDSSCs)has attracted much attention.There are several reasons:low cost,simple components,non-toxic and high theoretical efficiency.However,the current research efficiency of QDSSCs is 14%,which is only one-third of its theoretical efficiency.One of the problems is the lower photoelectric conversion efficiency caused by the insufficient utilization of quantum dot sensitizers for sunlight.As a commonly used photoanode materials,TiO2 limits the photoelectric performance of QDSSCs because of its band gap width,high density trap state and low photoelectrons injection efficiency causing the rapid recombination of photoelectrons and holes.Therefore,the research on QDSSCs'photoanodes,especially TiO2,is also a new research direction.In view of the shortcomings of TiO2 as a photoanodes,we use two methods to adjust the band gap of TiO2 and use it for photoanodes of QDSSCs.The following parts are about main research work of this paper:(1)In the first part,a simple hydrothermal method was used to synthesize a manganese-doped titanium dioxide(Mn-TiO2).The structure and morphology were characterized by XRD,FT-IR,Raman,UV-vis and FETEM.Compared with conventional TiO2,Mn-TiO2 has the advantages as QDSSCs' photoanodes.And then,the different amounts of Mn-TiO2 combined with commercially titanium dioxide applied to the photoanode films.Quantum dot sensitized using SILAR technique,then cells were assembled.Through J-V,EIS,M-S,OCVD and other electrochemical tests,the electrons transport and recombination inside the cell and the separation effect of Mn-TiO2 on the charge were analyzed.In particular,the Mott-Schottky curve shows that the flat band potential of the photoanodes containing Mn-TiO2 was more negative,so a higher open circuit voltage was obtained.Finally,with the increasing of amounts,the photoelectric conversion rate was the highest when 0.4g Mn-TiO2 combined with P25.An optimized open circuit voltage of 0.61 V and the short-circuit current of 11.5 mA·cm-2 for cadmium sulfide sensitized solar cells was received with a photoelectric conversion efficiency of 2.9%.(2)In the second part,hydrogenated titanium dioxide(H-TiO2)nanoparticles were successfully prepared by annealing TiO2 in mixed gas stream of H2/N2 at different temperatures.The structure and morphology were analyzed by XRD,FETEM and UVvis.XPS was used to determine the oxygen vacancy and its content in H-TiO2 after hydrogenation at different temperatures.The H-TiO2 nanoparticles prepared at different temperatures was used in the photoanodes of QDSSCs.At 500?,an optimized open circuit voltage of 0.67 V and the short-circuit current of 8.03 mA·cm-2 for cadmium sulfide sensitized solar cells was received with a photoelectric conversion efficiency of 2.81%.The enhancement of Jsc was attributed to the high donor density and the narrow band gap of H-TiO2,which promote the driving force of electrons injection.The increasing in voltage was due to the negative displacement of the flat band potential(Efb)of H-Ti02.