Study On The Preparation And Photoelectric Performance Of The Quantum Dots/Polyoxometalate Cooperating And Modifying With TiO₂ Nanotube Composite Films

With the intensification of the energy crisis increasing,the research of green renewable energy had become a hot topic for the scientists in various countries.Recently,since the exploring and developing,and widespread use,the high cost and complicated production process of solar cell became the main restriction factor for its promotion and application.Therefore,all over the word,the new material of solar cell became to the main developing direction,which had the low cost and high conversion efficiency.The materials of TiO₂,had the properties of semiconductor performance,and achieved positive results in the field of photo-voltaic cells.However,due to the wide band gap of TiO₂,it only adsorbed ultraviolet light in sunlight,resulted to a lower photoelectric conversion efficiency,the lower electron injection rate and easily recombined of electron-holes.Therefore,this material must be assisted by other materials to broaden the absorption range and electron injection rate.In this article,the method of successive ionic layer adsorption and reaction?SILAR?was used to papared the CdS/PbS/Ti O₂ nanotube composite thin film.Due to the advantages of the multiple exciton effect and size effect of quantum dots,the electron density was increased and the solar absorption range of the TiO₂ nanotubes extended to the visible spectral region.An ideal CdS/Pb S/TiO₂ nanotube composite thin film photoelectrode was obtained by optimizing the three experimental conditions of the concentration of the anion and cation in precursor solution,the cycle time,and the number of cycles.Then the TiO₂nanotube composite film was assembled into photovoltaic cells,and studied its photoelectric conversion efficiency.The results showed that the photoelectric conversion efficiency of the CdS/PbS/TiO₂ nanotube composite thin film photoelectrode was 3.95%,which were 2.9 and 2.3 times of the single quantum dot sensitized PbS/TiO₂ and CdS/TiO₂ nanotubes photoelectrode,respectively,and it is 5 times of pure Ti O₂nanotubes.The effective matching of CdS and PbS bandgap was more favorable for photoelectrons injection and holes regeneration,it reduced the electron-hole recombination and played role in co-sensitization of PbS/CdS.In addition,it improved the photoelectric conversion efficiency of TiO₂nanotube composite electrode.In order to further improving the photoelectric conversion efficiency of the quantum dot sensitized TiO₂ nanotube composite film,this article was used the characterization of the polyacids with the ability to accept electrons,the Ti O₂ nanotubes were are co-sensitized with the synergistic action of CdS and SiW₁₂,PW₁₂.Orthogonal test were used to optimize the conditions,including the polyacids concentration,and deposition time,CdS QDs concentration,the cycles number,and deposition sequence of polyacids and CdS QDs,papered SiW₁₂/TiO₂,CdS/SiW₁₂/TiO₂,SiW₁₂/CdS/TiO₂,PW₁₂/TiO₂,CdS/PW₁₂/TiO₂,PW₁₂/CdS/TiO₂ nanotube composite films.Its morphology,crystal structure and growth mechanism were charactered.Then the above Ti O₂ nanotube composite films were assemble into photovoltaic cells,and studied its optoelectronic performance.The results showed that the photoelectric conversion efficiency of CdS/SiW₁₂/TiO₂ nanotube composite films was up to 14.2%,the open circuit voltage reaches 3190mv and the closed circuit current reaches 103.9?A/cm²,which was about 1.3 times higher than the photoelectric conversion efficiency of SiW₁₂/CdS/TiO₂ nanotube composite thin film,and about 1.9 times that of SiW₁₂/TiO₂ nanotube composite thin film,and about 52.6 times that of TiO₂ nanotubes.The photoelectric conversion efficiency of CdS/PW₁₂/TiO₂ nanotube composite film was up to 11.7%,the open circuit voltage reaches 2890mv and the closed circuit current reaches 97.1?A/cm2.which was about 1.1 times of the PW₁₂/CdS/Ti O₂ nanotube composite film,about 1.2 times of the PW₁₂/TiO₂ nanotube composite film,and about 43.3 times of the TiO₂ nanotube.Through the above analysis of results,we could obtain that the sensitization of TiO₂ nanotubes with CdS QDs and H₄SiW₁₂O₄₀ and H₃P₁₂O₄₀ effectively broaden the absorption range of TiO₂ nanotubes,suppressed the recombination of electron-holes,and increased the electron density on the surface of TiO₂nanotubes and the use of sunlight,and greatly improved the optoelectronic performance of Ti O₂ nanotubes.