Synthesis Of â… -â…¢-â…¥₂Semiconductor Nanoparticles And The Thin Films Preparation

In the recent decades, nano-materials have remained of great interest due totheir unique optical and electrical properties, which are different from those of thecorresponding bulk materials. Fabrications of thin-film solar cells based on“semiconductor nanocrystal inks” have become a hot topic of photovoltaic applicationsbecause of simplified and low-cost device fabrication, large-area coverage, and uniformfilms deposition. However, implementation of this technology still depends on the availableof high quality “nanocrystal inks” via a simple route. In this dissertation, we reported thesynthesis of high quality â… -â…¢-â…¥₂ternary semiconductor nanocrystals via a simple andgreen solution route, the effects of reaction time, growth temperature and crystal structureon the size and morphology of nanoparticles have been investigated. We also prepared the“nanocrystal ink” by the as-prepared CuInSe₂nanoparticles, and fabricated CuInSe₂thinfilms by non-vacuum technologies. The effects of solvents and atmosphere of thermaltreatment on the quality of films have been investigated. The main achievements are listedas following:1. High quality AgInSe₂nanoparticles were synthesized via a simple soltuionroute using environmentally friendly N-oleylmorpholine as the solvent of Sepowder and oleylamine as capping ligand, respectively. The TEM images and XRDpatterns reveal that the as-prepared hexagonal-plate shaped AgInSe₂nanoparticleswith chalcopyrite structure have an average size about16nm. After comprehensiveanalyzing the crystal structure of the chalcopyrite structure and the differentmorphologies of nanoparticles synthesized at different temperature, aninvestigation of the shape evolution was performed by selective adsorption ofoleylamine modules and the law of Bravais. The effect of reaction time on the sizeof AgInSe₂nanoparticles was also investigated, and the results showed that the sizeof nanoparticles was increased with prolonged reaction time.2. AgInS2nanoparticles were synthesized at low temperature via the samesolution route using N-oleylmorpholine as the solvent of S powder. From the XRDpatterns, all the diffraction peaks can be assigned to the orthorhombic-phase whichis a high-temperature phase. The reason might be that the solvent N-oleylmorpholine has changed the chemical growth environment, leading to thephase reversion temporarily. Worm-like nanorods were obtained by altering thereaction temperature, and this is further evidence that the shape of nanocrystals ismainly determined by their inherent crystal structure.3. Chalcopyrite CuInSe₂nanoparticles were also synthesized by this route and theas-prepared CuInSe₂nanoparticles can be used to prepare “nanocrystal inks” byprecipitation and redispersion in organic solvents. We demonstrated the utility ofthese inks in solar cells fabrication. The CuInSe₂films were formed bydrop-casting or spin-casting on ITO coated glass substrate and annealed under flowof H2or Se vapor at different temperature. The SEM images show that uniform andnearly crack-free films are deposited by spin-casting from concentrated high bolingpoint tetrachloroethylene dispersions. On the other hand, the films annealed underSe vapor are more compact than those under flow of H2, and the EDS patternsreveal that the films are nearly stoichiometry. The films can be applied in solarcells as absorber layers.