Preparation And Performance Investigation Of Titanium Dioxide Based Photoanode For Quantum Dots Sensitized Solar Cells

Energy crisis and environmental pollution have become two serious problems facing the world with the development of human society and technologies.Solar energy is one of the most potential new energy sources due to its large reserves,universality,clean and renewable advantages.As the third generation solar cells,quantum dot sensitized solar cells?QDSSC?have attracted great attention because of their multi-exciton effect,small band effect and size-adjustable band gap,which can theoretically achieve higher photoelectric conversion efficiency.However,the photoelectric conversion efficiency of quantum dot-sensitized solar cells is far behind the traditional silicon-based solar cells and the latest perovskite solar cells due to the low effective quantum dot loading rate,high electron transmission resistance,serious interface charge recombination,narrow absorption range and other factors.Therefore,in order to improve the effective loading rate of quantum dots,the transmission efficiency of photogenerated hot electrons,the absorption range of photoanode,the absorption intensity of visible light and optimize interface,we designed and realized the porous TiO₂ nanoparticle thin films,TiO₂ nanoparticle/nanosheet composite structure,high photoluminescence up-conversion nanoparticles doped TiO₂nanoparticles thin films,Au nanoparticle-decorated TiO₂ nanorod array.Above mentioned thin films were applied to the photoanodes of quantum dot sensitized solar cell.The effects of these structures on the performance of solar cells have been studied in detail.The main researches and results are summarizeas follows:?1?Carbon nanoparticles were synthesized by microwave synthesis method.Mesoporous titanium dioxide nanoparticle thin films with high effective specific surface area were designed and prepared using carbon nanoparticles as template.The effects of different mixing amounts on the performance of QDSSCs were studied.The results show that the titanium dioxide nanoparticle thin films prepared by using carbon nanoparticles as templates have higher quantum dot loading rate.The holes formed by carbon nanoparticle can improve the light scattering ability and facilitate the full contact between electrolyte and photoanode.The optimum experimental conditions were determined when the content of carbon nanoparticles was 15%.The photoelectric conversion efficiency of 4.41%is obtained.Compared with pure TiO₂ nanoparticle,the efficiency is increased by 35.3%.?2?Anatase TiO₂ nanosheets with high active surface were prepared by hydrothermal synthesis method.In order to make full use of the advantages of high specific surface area of nanoparticles and faster electron transport ability of nanosheets,TiO₂ thin films with two morphologies were prepared.The relationship between different mass ratios and photoelectric properties was studied in detail.When the mass ratio of nanoparticles to nanosheets is 2:3,the specific surface area advantage of nanoparticles and the electronic transmission advantage of nanosheets are maximized.Compared with pure nanoparticles?3.61%?and nanosheets?4.57%?,the photoelectric conversion efficiency of nanoparticles is 4.98%.The composite structure can effectively improve the effective optical path and reduce the resistance of electron transmission.The incorporation of nanosheet can introduce pore structure,which can improve the wettability between polysulfide electrolyte and photoanode.?3?In order to improve the utilization efficiency of sunlight and enhance the visible light response intensity to broaden the absorption spectrum,NaYF₄:Yb³⁺,Ho³⁺,Fe³⁺@SiO₂@Au core-shell structure nanoparticles were prepared and introduced into TiO₂nanoparticle thin film.The introduction of NaYF₄:Yb³⁺,Ho³⁺,Fe³⁺@SiO₂@Au nanoparticles could convert near-infrared light into green and red light,which could be absorbed by CdS and CdSe quantum dots.The interface between gold shell and titanium dioxide can produce obvious surface plasmon resonance effect,which can effectively improve the efficiency of electron extraction and separation of titanium dioxide skeleton structure.Silica in the middle layer can obviously improve the scattering ability of light and realize the secondary utilization of light.Gold shell can also improve the electronic transmission properties of titanium dioxide thin films.The effect of mixing amount on the performance of quantum dot sensitized solar cells was studied in detail.When the mixing content exceeds 7%,the short-circuit current decreases,which may be attributed to the loss of active sites for quantum dot deposition.The measurement of specific surface area confirms this view point.The enhancement of photoelectric performance caused by additional 980 nm lasercontinuous irradiation confirms the absorption ability of the photoanode in near infrared band.The photoelectric conversion efficiency of 6.18%confirms that the introduction of up-conversion nanoparticles can be a feasible method to improve the photoelectric conversion efficiency of quantum dot sensitized solar cells.?4?A large area of uniformly vertically grown titanium dioxide nanorod arrays were fabricated on FTO conductive glass substrates by hydrothermal synthesis method.Then gold nanoparticles modified TiO₂ nanorod arrays were fabricated by in situ deposition and heat treatment method.The introduction of gold nanoparticles optimized the interface between titanium dioxide nanorod arrays and CdS quantum dotson the one hand,introduced surface plasmon resonance effect on the other hand.The effect of deposition time of gold nanoparticles on photoelectric conversion efficiency was investigated in detail.When the deposition time of Au nanoparticles is 3 hours,the photoelectric conversion efficiency of the cell reaches the best of 3.29%?pure CdS quantum dots as sensitizer?.The deposition of Au nanoparticles obviously increases the short circuit current but decreases the open circuit voltage,which is attributed to the side reaction between excessive Au nanoparticles and electrolyte.Excessive Au nanoparticles can also lead to the loss of active sites for quantum dot deposition,resulting in the reduction of short-circuit current.