Synthesis Of CuInS₂ And CuInS₂/ZnS Quantum Dots With High Photoluminescence And Their Continuous Process Development

CuInS₂ ?CIS? quantum dots ?QDs? have great potential applications in the field of biology and photovoltaic due to its low-toxic, high sunlight absorption coefficient and good photostability, however the low photoluminecent ?PL? efficiency, poor quality control, and the lack of large scale production of CIS QDs limited its wide application. This dissertation is focus on the synthesis development of CIS and core/shell CIS/ZnS QDs with high quantum yields ?QYs? based on their PL emission mechanism and particle growth dynamics. The tunable emission wavelengthes with high QYs were obtained by adjusting process parameters. Furthermore, the continuous process for CIS and CIS/ZnS QDs synthesis in microreactor system was development based on the flask batch synthesis technology. Finally, taking the large production of CIS QDs as an example, the engineering concept design based on microreaction system was carried out to estimate total investment cost and production cost of CIS QDs. In total, the entire life cycle of CIS QDs from lab research to production was conducted and main results were stated as following:?1? QY improvement of CIS QDs by high temperature heat treatment in solventHigh temperature heat treatment in solvent to improve QYs of CIS QDs was developed. The PL emission mechanism of CIS QDs and the effect of heat treatment to crystallinity and PL QYs were studied. The results showed that CIS has PL emitting with multiple levels and the donor-acceptor emission was main emission. The non-radiation recombination from a variety of surface and internal defect of CIS nanocrystal caused the low QYs. The nanocrystal had redissolved and grown in organic solvent with ligands at the high temperature, which reduced the impurities, internal and surface defects of crystals and then the QY of CIS QDs was increased from 5.7% to 10.8%.?2? Synthesis of broad color-emitting CuInS₂/ZnS QDs at low temperatureCore/shell CIS/ZnS QDs were synthesized with zinc diethyl dithiocarbamate ?ZDC? as ZnS precursor material and trioctylphosphine ?TOP? as the main capping ligands below 200?, The growth of ZnS could start at 150? since low decomposition temperature of ZDC. The influence of ZDC amount, shell growth temperature and time, CIS core reaction time, and types of ligands to optical properties were investigated. The QYs of CIS/ZnS QDs were influenced by two aspects:on the one hand, ZnS growth on CIS surface reduced its surface defects and therefore increased PL efficiency; on the other hand, and organic TOP layer formed on the surface of nanocrystals is also as hole acceptor which generated non-radiative recombination. In total, the improvement of QYs of CIS/ZnS QDs was limited. Meanwhile, the extonic absorption was observed while TOP was used as ligands. Furthermore, ZDC coordinating with TOP at low temperature increased its'reaction activity, which could speed up the shell growth rate and CIS/ZnS with higher thickness of shell was obtained, which broaden PL emission wavelength to around 550 nm.?3? Synthesis of gradient core/shell CIS/ZnS QDs with high photoluminescenceCIS/ZnS QDs were synthesized using zinc acetate as ZnS precursor materials, dodecanethiol as both S source and ligands at above 200?. The structure obtained QDs was traced as a core/shell structure with a gradient chemical composition ?Zn-CIS? between CIS core and ZnS shell by coupled plasma-optical emission spectroscopy ?ICP-OES?, X-ray photoelectron spectroscopy ?XPS?, transmission electron microscopy ?TEM? and PL spectra analysis. The emission mechanism of CIS/ZnS was analyzed by two Gaussian functions and time-resolved PL spectra, which indicated free-to-bound emission was the main emission. The growth of ZnS and gradient core/shell structure could improve the QYs significantly. PL QY of CIS/ZnS QDs was enhanced up to 80% through investigating and optimizing the reaction parameters. The prepared CIS/ZnS QDs had high photostability in ambient condition since ZnS surface could keep QDs from oxidizing.?4? Continuous synthesis of CIS and CIS/ZnS QDs via microreaction systemMicroreaction system including micro mixer, micro heat exchanger and microreactor was set up based on modules from Bayer. CIS and CIS/ZnS QDs were synthesized continuously based on microreaction system. Due to highly efficient heat transfer and mass transfer of microreactor, the reaction parameters can be precisely controlled and required reaction time was shortened. The maximum QY of obtained CIS QDs was up to 13.7%. The PL emission wavelength of CIS QDs could reach to 618 nm even without coating of ZnS shell and the free-to-bound emission was the main emission. Uniformed CIS QDs with different morphology and crystal phase approached using different ligands such as oleylamine, oleic acid, etc. The totally continuous synthesis of CIS/ZnS QDs was demonstrated using TOP as ligands at shell growth step.?5? Process concept design & captical investment evaluation of CIS QDs based on microreaction system in large-scale productionThe size of microreactor was estimated and engineering concept design was carried out based on lab result under the setting annual capacity of 100 kg of CIS QDs. The estimated total captical investment for construction of the project is expected to around 7.4 million, and the total production cost of about 31 million. In turn, the calculated CIS cost price is 0.31 RMB/mg, which has significant benefit compared to the marketing price of 80 RMB/mg. Equipment cost have little impact on the production cost from the return on investment analysis, therefore more attention in future should be develop suitable reactor for sustainable CIS production with high quality. Microreaction technology is currently the prefered choice for large-scale production with quality-controllable and fast scaling-up.