SnS Nanocrystals And Films Synthesized By Polyol Solution Chemistry

Narrow ba ndgap IV-VI semiconductors have be en w idely used in fields of near-infrared ( NIR) - infrared (IR) detctors, s olar c ells a nd telecommunications relays for t heir e xcellent ph otoelectric e ffect. Thereinto, SnS pos sesses d irect bandgap 1.3eV, indirect bandgap 1.1eV, good absorption of visible light with optical absorbance >104cm-1, and theoretical photoelectric efficiency of 25% for solar cell application as P type materials.In this thesis, SnS nanocrystals were prepared by hot-injection method using diethylene glycol as solvent, tin (II) chloride and thioacetamide as tin precursor and sulfur precursor respectively, PVP as dispersing agent and alkaline triethanolamine (TEA), ammonia (NH3·H2O), hydrazine hydrate (N2H4·H2O) as additives. The effect of pr ocess pa rameters s uch as sulfur pr ecursors, injection ways, r efluxing temperatures, refluxing time and additives etc on the morpology, structure and optical properties were investigated.The experimental results showed that the injection ways affected crystal size of the synthesized nanocrystals. The reaction rate can be adjusted by applying different adding amounts of additives, which further controlled nanocrystal size. Refluxing temperature and refluxing time could also alter nanocrystal size and kind of additives and its amounts have great effects on crystal phase.In TEA-added system, when TEA amount was low, the obtained nanocrystals were mainly zinc b lende s tructure w ith nanosheet morphology. When T EA a mount was high, the obtained nanocrystals were orthorhombic structure with nanorod morphology. Refluxing temperature and time had little effect on nanocrystals for this system. In NH3H2O-added system, the results were similar to the TEA-added system. In N2H4H2O-added system, fine n aocrystals with spherical m orphology w ere obtained a nd the r efluxing temperature a nd time a ffected the morphology o f nanocrystals a lot. By controlling the refluxing temperature and time, SnS nanocrystals with size of 8~13 nm could be obtained. Zinc blende structure and orthorhombic structure differed a lot in optical bandgap structure. Orthorhombic SnS posessed direct band gap 1.3 eV and indirect band gap 1.1 eV, and zinc blende structure had a forbidden bandgap 1.7eV. Both had a good stoichiometry. The SnS films were prepared by dip-coating method using colloidal ink which was prepared by redisperseing well dispersed nanocrystals into alcohol. The as-prepared films were dense and smooth, but had phase transition to SnS2 after annealing.