Texture And Electrical And Optical Properties Of FeS₂ Thin Films

The polycrystalline FeS₂ (pyrite) with a cubic system has shown an important research value to develop into a promising candidate for the manufacture of solar energy cells due to its suitable energy band gap, high optical absorption coefficient, abundant constituent resource in nature, excellent environmental safety and low preparation cost.In this thesis, the FeS₂ thin films were prepared by thermal sulfurizing the precursory Fe films. The effects of substrates, thicknesses, sulfurizing times on the texture were investigated. Electrical and optical properties of pyrite thin films influenced by the grain sizes were also analyzed. TiO₂ thin films were also prepared by sol-gel and dig coating method in this thesis. Then FeS₂ thin films were prepared on the TiO₂ films by electrodeposition and sulfurization methods to form the FeS₂/TiO₂ composite films. The microstructure, morphology, electrochemical properties of composite films with different depositing times and sulfurizing temperatures were studied. The main conclusions can be drawn as following:There are different effects of substrates, thicknesses, sulfurizing times on the pyrite texture. Pyrite film prepared on the Al(111) substrate has high (200) orientation, and FeS₂ films prepared on the Si(100) and Si(l 11) do not present obvious crystallographic orientation. However, there are both preferred orientations (200) and (220) in the FeS₂ films sputter substrate of TiO₂ films. The level of preferred orientation (300) becomes higher as the thickness of FeS₂ film increase due to the increasing ratio of upper layer columnar crystal. The variety of the sulfurizing time cause the variety of crystal interface area, therefore the sulfurizing time restricts the texture of FeS₂ film. During the 10 to 20 h sulfurization, the texture decreases largely, whereas the texture becomes stable after 20 h sulfurizaion.The FeS₂ films present p-type conduction with different grain sizes. The resistivity of the film linearly changes with the grain size. However, the carrier concentration has inverse-proportional relationship with grain size. This rule can be derived by the point defeat created by crystal interface mechanism. With the grain size increasing, the absorption coefficient of the light increases first and then decreases, and the bandgap has the similar trend as absorption coefficient. This trend is cause by transition phase and crystal interface. To the FeS₂/TiO₂ composite films, the photocurrent increase then decrease with the depositing time increase because of coverage and compaction of FeS₂. The photocurrent increase then decrease with the sulfurizing temperature increase because of the crystallinity and compaction of the FeS₂.