Synthesis Of Zn_xCd_1-xSe Alloyed Quantum Dots In Aqueous And The Application For Solar Cells

Because of the unique properties of quantum dots (QDs), such as quantum confinement effect, multi-exciton effects and high extinction coefficient, it has been applied in the third generation of solar cells-quantum dot sensitized solar cells (QDSSCs). However, quantum dots have become a hot research in solar cell area and been as a new type of sensitizing agent material, replaced dye-sensitized molecules.In this work, tunable-bandgap ZnxCd1-xSe quantum dots using thiol stabilizer were synthesized in aqueous phase. The sample morphology, crystalline structure, absorption and emission spectra were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy spectrum analysis (EDS), UV-Visable spectrophotometer (UV-Vis) and fluorescence spectrophotometer (PL), respectively. In addition, ZnxCd1-xSe quantum dots were sensitized on TiO2 nanotubes prepared by anodic oxidation and ZnO nanorods prepared by hydrothermal method, respectively. Characteristics of as-prepared photoanode materials were via UV-Vis, XRD, EDS, scanning electron microscopy (SEM) and electrochemical workstation. The main contents and conclusions were as follows:(1) Tunable-bandgap ZnxCd1-xSe QDs were prepared using SeO2 as selenium source by one-step aqueous phase. The results showed 3-mercaptopropionic acid (3-MPA) capped ZnxCd1-xSe quantum dot particles were approximately spherical with about 3.5 nm and cubic zinc blende crystal structure. The as-prepared QDs had broad absorption range, tunable-bandgap in the visible area and the best fluorescent performance. So ZnxCd1-xSe QDs were as photosensitizers.(2) Firstly, TiO2 nanotube arrays which were highly ordered were prepared by anodic oxidation process. Secondly, ZnxCd1-xSe QDs were used to sensitize TiO2 nanotubes by direct adsorption (DA), chemical bath deposition (CBD) and succession ion layer adsorption and reaction (SILAR), respectively. The study about ZnxCd1-xSe/TiO2 nanotubes assembled by SILAR found that its photoelectric conversion efficiency was up to 1.3%, when the deposition cycles were 6 cycles. Compared with the other methods, the spectral response range of anode materials prepared by SILAR was broader, and its efficiency was 1.11 higher than CBD (1.17%), and 3.8 higher than DA (0.342%), respectively. It also demonstrated that the solar cells were formed heterojunction structure between quantum dots and TiO2 nanotubes by using in situ deposition, such as CBD and SILAR, which could enhance the photocurrent densities.(3) Regular morphology of ZnO nanorods were prepared via hydrothermal method. ZnxCd1-xSe/ZnO nanorods were assembled via DA, CBD and SILAR, respectively. In addition, MnxCdySe/ZnO nanorods anode materials were deposited though SILAR. The study of ZnxCd1-xSe/ZnO prepared by SILAR found that its photoelectric conversion efficiency was 2.69%, when the deposition cycles were 4 cycles. Compared with the other methods, its efficiency was 1.007 higher than CBD (2.67%), and 7.75 than DA (0.347%), respectively. It should be caused by the ex situ of DA. However, the study about MnxCdySe/ZnO nanorods anode materials deposited via SILAR found that the photoelectric conversion efficiency of anode materials was 0.503%, corresponding to 6 cycles of the deposition cycles.