Preparation And Characterization Of CuInS₂ And Zn_2x(CuIn)_1-xS₂ Alloyed Semiconductor Nanocrystals

In recent years, semiconductor nanocrystals (SNCs) have drawn much attention due to their unique tunable optical and electronic properties as well as their promising applications in nanodevices. As aâ… -â…¢-â…¥2 ternary semiconductor compound, copper indium disulfide (CuInS₂) can be applied to fabricate solar cell, whose conversion efficiency in solar cells has been calculated to reach 28%～32%, the highest among all of the photovoltaic devices owing to its high absorption coefficient and direct band gap of 1.50eV which is close to the best band gap of the solar cell materials (1.45eV). In comparison with CuInSe2, CuInS₂ is an environmentally benign material with no toxic composition. Therefore, CuInS₂ is a kind of promising solar cell material. But there are some primary problems as complicated manufactural process and high cost that counteract the industrialization of CuInS₂ solar cell.This dissertation focuses on the controlled preparation and characterization of Groupâ… -â…¢-â…¥2 ternary alloyed compound CuInS₂ SNCs and Groupâ… -â…¡-â…¢-â…¥2 quarternary alloyed compound Zn2x(CuIn)1-xS₂ SNCs. Firstly, CuInS₂ and Zn2x(CuIn)1-xS₂ alloyed SNCs were successfully synthesized under mild condition via solvothermal method with simple operation, low cost, no toxicity and advantages of industrialization. Secondly, the reaction condition of synthesizing CuInS₂ SNCs was studied, including solvent (ethylene glycol and triethyleneglycol), reaction temperature (180℃and 250℃), S-source (sulphur precipitated and thiourea), ligand (ethylenediamine and oleylamine), ligand dosage (0 ml, 5 ml and 20ml) and injection mode (simultaneity and stepping) etc. We finally determined the optimized conditions as follows: Choose ethylene glycol as solvent; reaction temperature is 180℃; Use precipitated sulphur as S-source; Inject 5 ml ethylenediamine ligand and take simultaneous injection mode. Finally, the as-prepared CuInS₂ and Zn2x(CuIn)1-xS₂ (x=0, 0.25, 0.40, 0.61 and 1)alloyed SNCs were characterized by XRD, TEM, SEM, EDS, XPS, ICP, UV-vis, etc. The surface morphology of these samples was complicated. It was realized that the composition and structure were successfully controlled: lattice parameter was decreased with the increase of x and the structurechanged from tetragonal chalcopyrite to cubic zinc blend. The band gap (Eg) of the samples was also tunable from 1.48eV to 3.48eV: absorption edge was gradually decreased with the increase of x. As a result, band gap was gradually decreased with the increase of x, and absorption edge can cover the whole visible light spectrum, even extending to near-infrared and ultraviolet range. The nonlinear relationship between band gap and composition was observed.