Abstract
In this dissertation, we describe the synthesis and applications of metal chalcogenide nanocrystals. To give a clear picture of this dissertation, the main contents are summarized as follows: (1) Ternary, quaternary and quinary CuIn1-xGax(SySe1-y)2 nanocrystals were synthesized and investigated. (2) CuGaS2 nanomaterials were prepared with size, morphology and crystal phase control. (3) CuIn1-xGax(SySe1-y)2-based (CIGSSe-based) thin film solar cell preparation. (4) Binary metal chalcogenide nanocrystals for dye-sensitized solar cells (DSSC) applications. We have developed a heating-up method to synthesize high quality nanocrystals. Using this method, 15~30 nm nanocrystals in oleylamine were synthesized and the quantity could be easily scaled up by this approach. The nanoparticles were analyzed by several instruments. The composition of nanoparticles can be tuned through the change of the element precursor ratios in the synthesis. The colloidal synthesis of quinary nanocrystals with entire composition tuning was achieved and band gap engineering could be tuned in the range from 0.98 eV to 2.40 eV. We have also characterized the band gap energy of CuIn1-xGax(SySe1-y)2 nanoparticles in both experimental and theoretical ways. Size, shape and crystal phase of CuGaS2 nanomaterials can be manipulated by changing the experimental parameters. With the size-selection approach, different sizes of nanoparticles can be separated. By exploiting different reactants and capping agents, different shapes of nanomaterials were obtained. We also discussed the growth mechanism by changing the reaction temperature at the last part. A variety of solution-based coating methods, such as spray deposition, dip-coating, and doctor blade coating have been applied for film deposition in this study. The qualities of thin films deposited from different methods were compared. Finally, CuIn1-xGax(SySe1-y)2 nanoparticles were coated on the Mo substrate by spraying deposition. After selenization process, buffer layer deposition, and top electrode sputtering, CuIn1-xGax(SySe1-y)2 nanocrystals as optical absorbing materials for solar cell devices were demonstrated. The devices had the cell efficiency over 1%, proving that these nanoparticles are promising precursors for photovoltaic devices. Binary metal chalcogenides nanocrystals, Co9S8 and FeSe2, were proved to be the materials of counter electrode for DSSC. Through non-vacuum deposition methods, spray coating and electrophoretic deposition, binary metal chalcogenides nanocrystals can be deposited onto the conductive substrates. According to the analysis of cyclic voltammetry, Co9S8 and FeSe2 have good catalytic ability toward I-/I3- redox reaction. In addition, the DSSC assembled with Co9S8 and FeSe2 counter electrodes were demonstrated and the cell efficiencies of over 7 % were obtained.