Fabrication And Characterization Of CuInS₂ And ZnO Thin Films Window Layer Materials For Solar Cells

CuInS2 thin film has a direct band gap of 1.53 eV, which is well matched with the solar spectrum, a high absorption coefficient of about 105 cm-1 and an exceptional insensitivity to radiation damage or impurity. CuInS2 has become a promising absorber material of thin film solar cells, which is also an environmental friendly material because it does not include high toxic components in itself.ZnO is a importantⅡ-Ⅵ, wide and direct optical band gap semi-conductive compound, which the band gap is 3.4 eV and the exciton binding energy is up to 60 meV at room temperature. ZnO is a particularly attractive material for thin film sensors, transparent electrode in light emitting diodes (LEDs), liquid-crystal displays. Furthermore, it has become increasingly important as window layer in solar cell because of its excellent electro-optical properties and great stability in presence of hydrogen plasma.CuInS2 thin films were prepared by sulfurization of sequentially deposited Cu-In stacks with elemental sulfur under N2 atmosphere. Mo back electrode was prepared on glass substrate by magnetron sputtering; Cu-In alloy precursor was prepared by DC magnetron sputtering on Mo layer. The Cu-In precursor was sulfurated with sulfur vapor to grow the CuInS2(CIS) absorption layer for solar cells.The fabbrication of ZnO nano-array thin films use two-step method:First,the seed layer was deposited by sol-gel technolog or magnetron sputtering.Second,ZnO nano-array thin film was synthsis from the aqueous solution using HMTA as the ammonia release reagent.The effects of the thin films with different grown condition on the morphology, microstructures and band gap were studied. The CuInS2 thin film and the ZnO nano-array thin film were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and UV-visible spectrum (UV-Vis).The results show that the chalcopyrite phased CuInS2 thin films with the preferred orientation of (112) can be prepared by sulfuration temperature at 550℃for 20 min. The CuInS2 thin films with an average grain size of 1μm and band gap 1.5 eV have been achieved. The results also show that the well-aligned nano-array thin films growed on the ZnO seed layer with survey and evenly surface can be prepared by growth temperature at 90℃and the concentration with 0.05M for 2h.The prepared nano-array thin films are favorable for electron transport and are suitable for window layers for solar cells.