Preparation And Characteristic Of Copper Zinc Tin Sulfur Films As Solar Cell Absorbers

As one of most promising absorber candidates in thin film solar cells,copper ZincTin Sulfur (Cu2ZnSnS4, CZTS) is paid more attention due to its innocuity, high efficiencyand low cost. CZTS has kesterte structure with a direct band gap of1.45eV which is closeto the optimum band gap (1.5eV) of absorber layer and the absorption coefficient over104cm-1. In addition, in theory its conversion efficiency reaches32.2%. All the aboveindicates that CZTS is suitable for the absorber layer in solar cells.In this thesis， CZTS thin films were fabricated by thermal evaporation andsulfurization method. Sn/Cu/ZnS (CZT) precursors were deposited by evaporation andthen sulfurized in sulfur atmosphere to produce polycrystalline CZTS films. The structural,morphological and photoelectrical properties of the fabricated CZTS thin films wereinvestigated, and the mechanism was explored. The main results are as follows:1. The properties of CZTS thin films with different metal atom ratio（n Zn/n Snandn Cu/(n Sn+n Zn)）was studied. The optimum metal atom ratio isn Cu/(n Sn+n Zn)=0.83andn Zn/n Sn=1.15which makes the CZTS in kesterte phase without other phases2. The influence of sulfurization temperature（300-550℃）and time（1-3h）on theperformance of CZTS films with the optimum metal atom ratio was investigated. It showsthat CZTS films fabricated at no less than500℃for3hours have a better crystallinity.The XRD analysis shows that the CZTS films grow with a strongly preferred (112)orientation and no other phases except for CZTS are found in the films. When thesulfurization time and temperature are3hours and500℃, the band gap energy, carrierconcentration, resistivity and mobility of the CZTS film are1.54eV,1.08×1017cm-3,5.38·cm and10.72cm2/(V·s), respectively, which meet the requirements of absorberlayers in solar cells.In this thesis, we also studied indium tin oxide (ITO) layer for the anti-reflectingfilms and transparent conductive electrodes in solar cells. ITO thin films were depositedon glass substrates by DC magnetron sputtering process. To meet the requirements oftransparent conductive electrodes in solar cells, the influence of sputtering power, substrate temperature and sputtering pressure on the structural, morphological andphotoelectrical properties of ITO films was also investigated. When the sputtering power,substrate temperature and work pressure are30W,150℃and0.4Pa, respectively, the ITOthin films exhibit good electrical and optical properties with low resistivity(3.574×10-4·cm) and high transmittance (>80%) in the visible wave band. Therefore, theITO thin films are suitable for the transparent electrodes of solar cells.