The Photoelectronchemical Performance Investigation Of CdS And Bi₂S₃ Sensitized SnO₂ Based Solar Cells

Quantum dot-sensitized solar cells（QDSSCs） have captured a lot of attention in recent years due to high photoelectric conversion efficiency, which arise from quantum confinement effect and exciton multiplier effect. Photoanode materials are losely linked with the electron injection, transport and recombination, which largely influence the power conversion efficiency of sensitized solar cells（SSCs）. Up to now, the research about TiO2 photoanode is the most extensive and mature, and more and more attention has also been focused on some other wide-gap semiconductor material except TiO2, such as tin dioxide（SnO₂）, zinc oxide（ZnO） and zinc stannate（Zn₂SnO₄）, etc. Among them, SnO₂ has been considered as one of the most promising candidate for photoanode materials because it possess excellent chemical stability and electrical properties. Its key advantages can be seen as follows compared to TiO₂: i) The carrier mobility of SnO₂ is two orders of magnitude higher than the TiO2; ii) It has a larger band gap（3.5eV） than TiO₂（anatase, 3.2 eV）, thus reduces the oxidative holes created in the valence band, which is able to give a long-term stability for SSCs. However, the performance of SnO₂ photoanodes are poorer due to the faster interfacial electron recombination which lead to a lower open-circuit voltage and fill factor. In this thesis, tin oxide is used as photoanode materials, interfacial engineering was carried out to improve CdS sensitized SnO₂ based QDSSCs photoelectrochemical properties. The major research contents and results are as follows:（1） SnO₂ nanocrystal for QDSSCs was synthesized by the solvothermal method, and SnO₂ nanocrystalline porous films were prepared by screen-printing. In this section, both the effects of the SnO₂ nanocrystal annealing treatment and the CdS QD stacked layers on the photoelectric conversion efficiency of the QDSSCs were studied. Research results show that SnO₂ nanocrystal treated by annealing is more suitable for QDSSC, and the appropriate number of CdS QD stacked layers is 15.（2） Cu S photocathode and polysulfide electrolyte were introduced to investigate the photoelectrochemical properties of SnO₂ based QDSSCs further. Then, interfacial engineering was carried out in order to suppress the back transfer of electrons. On one hand, blocking affection of SnO₂ blocking layer with different thickness was studied. On the other hand, we investgateed the influence of surface passivating treatment by Ba2+. The results show that blocking layers and surface passivating treatment can effectively suppress the back transfer of electrons and enhance photoelectrochemical properties of QDSSCs. And, with increasing the blocking layer thickness, the photovoltaic performance of QDSSCs present earlier increase and later decrease trend. Excessive thick blocking layers would lead to increase electron transport distance and decreasing electron collection efficiency at the same time, so that photoelectrochemical performance of CdS-Sensitized SnO₂ solar cells was further improved not any more.（3） To expand spectral response range of the SnO₂ based QDSSCs, Bi₂S₃ QD was deposited on SnO₂ nanocrystalline porous films by atmospheric pressure chemical vapor deposition（APCVD）. Bi₂S₃ sensitized SnO₂ solar cells was assembled and studied. Bi₂S₃ sensitized SnO₂ solar cells achieve an photoelectric conversion efficiency of 1.79% after passivation treatment by ZnS. 批 hotoelectrochemical performance of Bi₂S₃ sensitized SnO₂ solar cells are improved obviously compared to CdS sensitized SnO₂ solar cells.