Solution Chemical Synthesis Of II-VI Semiconductor Nanocryatals And Their Photoelectrical Application

CdSe and CdTe are important engineering-related II-VI group compound semiconductors. Nanoscale CdSe and CdTe have attracted great attention in the past decade due to unique properties supplying for potential luminescence and photoelectronic application. In this dissertation, Cd(NO3)2 / Na2SeO3 / H2O solution system, Cd(NO3)2 / Na2SeO3 / EG- Glycerin system and Cd(NO3)2 / Na2TeO3 / H2O system were used to synthesize CdSe and CdTe nanocyrstals, and influence of the preparation conditions was investigated, such as precursor concentration and ratio, reaction temperature and time, precursor injection program and so on. The products were characterized by XRD, FESEM, TEM, HRTEM, EDS, XPS, FT-IR, UV-vis. The chemical reaction and crystal growth mechanism of these reaction systems were discussed. The synthesized nanocrystals were used to assemble the simulative photovoltaic devices based on CdSe-sensitized TiO2 structure, CdTe-CdS and CdTe-CdSe heterogeneous structures, and the photocurrent-voltage characteristics were measured.The results showed that the CdSe nanocrystals prepared in aqueous solution tended to agglomerate. With increasing of Cd/Se ratio and reaction time, the CdSe nanocrystals tended to form one-dimension and dendritic structure. Wurtzite CdSe nanocrystals with narrow size distribution centered at about 6nm were synthesized by injecting the precursor solution into hot EG-Glycerin solvent as specific injection order. The as-prepared colloid performed resolved optical absorption and photoluminescence under incident light with wavelength of 480 nm. XPS results showed that the reduction of SeO32- to Se0 and disproportionation of Se0 took place during synthetical process and dominated chemical reaction. FT-IR analysis demonstrated that EG and Glycerin molecules had weak coordinating characteristic, which were contributed to the improvement of dispersion and colloidal stability of CdSe nanoparicles in solvent.Zinc-blende CdTe nanodots, nanorods and nanowires were successfully synthesized in Cd(NO3)2 / Na2TeO3 / H2O reaction system using L-cysteine as stabilizing agent under ambient pressure at relatively low temperature. L-cysteine contributed to 1D growth and dispersion of CdTe nanocrystals in aqueous soluteion.The precursor concentration mainly affected the lengths of the 1D nanoparticles and the ratio of Cd/Te affected both of the lengths and diameters. A proposed growth model was that combination of both the oriented attachment mechanism and the Ostwald ripening mechanism, which was demonstrated based on the direct HRTEM morphology evolution and the counted diameter frequency distribution of the resultant 1D CdTe nanocrystals.After purified, the nanocrystals were used to assemble the simulative photovoltaic devices based on CdSe-sensitized TiO2 structure, CdTe-CdS and CdTe-CdSe heterogeneous structures. The photovoltaic performance was characterized and carrier transport mechanism was analyzed. The measurement results showed that the open-circuit voltage and short-circuit current for CdTe-CdSe structure were 745.01mV and 11.78μA, respectively. The highest fill factor was 54.75%.