Preparation And Properties Of CdS And SnS₂Thin Films For Solar Cells

In this thesis, the preparation and properties of CdS and its alternative SnS2thin films for solar cells were investigated. The CdS thin films were deposited byultrasonic agitation chemical bath deposition (UCBD). The influence of annealingand CdCl2-treatment procedure on the surface morphology, crystal structure anddirect band gap of UCBD-CdS thin films was investigated. The effect of depositiontime on the grain size of CdS aggregates and stack denseness in the UCBD-CdS thinfilms was compared. The SnS2thin films were prepared by the technologies ofvacuum thermal evaporation and close-spaced sublimation, respectively. Theinfluence of the annealing temperature and source temperature on the chemicalcomposition, crystal structure, surface morphology, and optical band gap of the SnS2thin films were investigated.The results revealed that the UCBD-CdS thin film was homogeneous,free-crack and smooth. The small grains in CdS aggregates were melted together andthe CdS aggregate size was not changed in the UCBD-CdS thin films after theCdCl2-treatment procedure. The deposition time was very important to obtain thelarge grain of CdS aggregates and the dense UCBD-CdS thin films. In depositiontime of40min, the resulting UCBD-CdS thin films were dense and had the180nmgrain size of CdS aggregates and80.8nm of thin film thickness. The large grain anddense UCBD-CdS thin films were suitable for thin film solar cells as a window layer.Both the technologies of vacuum thermal evaporation and close-spaced sublimationcould deposit the SnS2thin films with high quality. The as-grown SnS2thin film byvacuum thermal evaporation was amorphous, homogeneous, smooth, no pinhole andcrack free nearly stoichiometric, and with an optical band gap of2.41eV. Alongwith the increase of annealing temperature, the SnS2thin films grew with bettercrystallinity,but the optical band gap were decrease. The SnS2thin films weresuitable for thin film solar cells as a window layer after annealed at300°C, with thecrystallization of SnS2was demonstrated by X-ray diffraction and scanning electron microscope with a characteristic of a preferred orientation along (001) plane withhexagonal phase and the sheet appearance of the SnS2crystals. The SnS2thin filmwas nearly stoichiometric, with a characteristic of a preferred orientation along (001)plane with hexagonal phase and the sheet appearance of the SnS2crystals, and withan optical band gap of2.42eV under the condition of the source temperature was580℃by close-spaced sublimation technology. The mixture film contained Sn2S3、SnS and S was obtained under the condition of the source temperature was650℃.The results demonstrate that the SnS2was physical sublimation under the conditionof the source temperature was580℃, and chemistry decomposition under thecondition of the source temperature was650℃. Therefore, the suitable sourcetemperature was580℃using for depositing SnS2thin film by close-spacedsublimation.