Fabrication Of Cu DOPED ZINC Sulfide Thin Films for 2nd Generation Photovoltaics

Abstract

Second generation photovoltaics technology has drawn remarkable attentions due to their facile and easy fabrication techniques. Zinc sulfide is considered to be the promising material for buffer layer in second generation photovoltaics because of its wide band gap and higher transmission coefficient. Undoped and copper doped zinc sulfide thin films are fabricated by spin coating method along with the fabrication of zinc sulfide thin films by RF magnetron sputtering for second generation photovoltaics. This thesis report is based on the comparison and analysis of undoped and copper doped zinc sulfide thin films along with magnetron sputtered zinc sulfide thin films as a buffer layer. To acquire crystallinity, the thin films were annealed at 5000 C in inert environment. XRD results revealed that deposited ZnS thin films at all copper concentrations by spin coating method have wurtzite structure, while ZnS thin films fabricated by RF Magnetron Sputtering have zinc blende structure. XRD pattern also depicted that at 6% copper concentration the extra peak of CuS phase is formed due to incomplete incorporation of copper. SEM analysis showed that deposited ZnS thin films by both sol gel method (undoped and Cu doped) and RF magnetron sputtering have compact, dense and homogeneous surface morphology without any voids and cracks. While, EDX spectroscopy confirmed that zinc to sulfur ratio is maintained in all ZnS thin films fabricated by sol gel method except ZnS thin films deposited by RF magnetron sputtering and ZnS thin films at 6% of copper concentration because of CuS secondary phase. FTIR absorption spectrum of ZnS thin films deposited by spin coating method confirmed the presence of ZnS vibrational bonds along with Vibrational and stretching bonds of carbon, oxygen and hydrogen. Optical analysis revealed that zinc sulfide thin film deposited by RF magnetron sputtering have maximum 76% transmission of light in visible region. By Tauc relationship calculated direct energy band gaps of all ZnS thin films are varied from 3.71 eV to 3.24 eV, which confirmed that incorporation of copper effected the energy band gap. Hall measurements confirmed that increase in copper concentration effects the carrier concentration, resistivity, mobility, conductivity and material type. All ZnS thin films deposited by spin coating method and RF magnetron sputtering have n-type material property except ZnS thin films at 6% copper concentration due to CuS phase formation.